Displays

Geodetic measurements of small rates of interseismic crustal motion made at high spatial resolutions and over large areas are crucial for understanding the earthquake cycle, characterizing spatial variations in lithosphere rheology and fault frictional properties, illuminating the mechanics of large-scale continental deformation, and improving earthquake hazard models. The densification of Global Navigation Satellite System (GNSS) networks has provided an unprecedented view of the kinematics of deforming regions. However, large gaps in spatial coverage still hamper our ability to fully characterize patterns of surface deformation. Interferometric synthetic aperture radar (InSAR), and the Sentinel-1 (S-1) satellites in particular, have the potential to overcome this obstacle by providing spatially continuous measurements of surface motions, without instruments on the ground, with precision approaching that obtained from GNSS, and at a resolution of a few tens of meters. In order to manage and process the large data volumes produced by S-1, we have developed open-source, automated workflows to efficiently generate interferograms and line-of-sight (LOS) velocity fields. These outputs are valuable for a range of applications, from earthquake rapid-response to investigating human-induced ground-level changes. In this talk, we demonstrate our ability to measure plate-scale interseismic deformation using data from the first ~5 years of the S-1 mission. We estimate LOS velocities for the Anatolian microplate, an area encompassing ~800,000 km² and including the highly seismogenic North Anatolian Fault Zone (NAFZ). By combining S-1 InSAR and GNSS data, we create high-resolution surface velocity and strain rate fields for the region, which illuminate horizontal deformation patterns dominated by the westward motion of Anatolia relative to Eurasia, localized strain accumulation along the NAFZ, and rapid vertical signals associated with groundwater extraction. Relatively low levels of strain characterize other active regions including the East and Central Anatolian Fault Zones and the Western Anatolian Extensional Province. We find that GNSS data alone are insufficient for characterizing key details of the strain rate field that are critical for understanding the relationship between strain accumulation and release in earthquakes. We highlight two important results stemming from our work including probabilistic estimates of the recurrence times of earthquakes of varying magnitudes for the region and a new NAFZ locking distribution that shows close correspondence to the surface rupture extents of large 20^th century earthquakes.

How to cite: Weiss, J., Walters, R., Wright, T., Morishita, Y., Lazecky, M., Wang, H., Hussain, E., and Hooper, A.: Measuring Anatolian plate velocity and strain with Sentinel-1 InSAR and GNSS data: implications for fault locking, seismic hazard, and crustal dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11156, https://doi.org/10.5194/egusphere-egu2020-11156, 2020.

We examine the kinematic characteristics of the crustal deformation in the broader southern Aegean region using 47 permanent GNNS stations distributed across the eastern Peloponnesus, Attica, Cyclades, Dodecanese, Crete and the coast of western Anatolia. Our analysis is based on the study of velocity vectors relative to local reference points at the western and eastern halves of the study area, as well as on the strain field calculated from absolute velocity vectors across the study area. We demonstrate that the South Aegean region undergoes complex distributed block deformation.

At the eastern end of the study area this varies from N210°-N220° extension and with crustal thinning across NE Peloponnesus – Attica, to N210°-N220° compression between the central-eastern Peloponnesus and western Crete, both consistent with the geodynamic setting of the Hellenic Subduction System.

A principal feature of the S. Aegean crust appears to be a broad shear zone extending between the islands of Samos/Ikaria and Kalymnos, Paros/Naxos and Amorgos and Milos – Santorini; It exhibits left-lateral kinematics and its southern boundary appears to coincide with the Amorgos – Santorini ridge and comprise the Anhydros basin and associated volcanic field (including Columbo and Santorini). Significant WNW-ESE crustal thinning is observed within the zone.

The area of the Dodecanese, to the south of Kalymnos and east of Astypalaea and north of Rhodes appears to undergo severe crustal thinning in the NW-SE direction while the SE  rim of the Aegean Plate appears to undergo thinning in the NE-SW direction. Finally, the abrupt increase in velocity between eastern Crete and Karpathos island indicates the presence of a very significant N-S tectonic boundary of unknown as yet nature, extending between 35°N and 36°N at least.

In order to assign some values to the above qualitative description, we note that with respect to a reference point at Anavyssos, Attica, the distribution of velocities allows identification of four and possibly five major tectonic blocks with different kinematics, whose location, direction of motion and average velocities respectively are:

• Samos – Ikaria and Naxos-Paros-Amorgos group of islands, N220° and 1.5mm/yr respectively.
• The south-western Cyclades (Anafi, Ios, Antiparos, Milos, Folegandros, Sikinos and Santorini group of islands, N210° and 3.3 mm/yr.
• The northern Dodecanese (Kalymnos, Kos, Astypalaea group), N150° and 3.0 mm/yr.
• The southern Dodecanese (Nisyros, Telos, Rhodes, Karpathos group), N120° and 7.4 mm/yr respectively.
• The Cretan Sea and Crete, N160° and 2.0 mm/yr respectively.

An interpretation of the nature and kinematics of the boundaries between these blocks will be presented and discussed. Overall, the south Aegean appears to undergo distributed block deformation associated with a rather complex kinematic pattern, the nature of which remains to be confirmed, validated and explained with future research.

Acknowledgements. This presentation was financially supported by the Special Account for Research Grants of the National & Kapodistrian University of Athens.

How to cite: Sakkas, V., Doxa, C., Tzanis, A., and Kranis, H.: Contemporary Kinematics of the South Aegean Area (Greece) Detected with Continuous GNSS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7656, https://doi.org/10.5194/egusphere-egu2020-7656, 2020.

Tearing in the Hellenic slab below the transition between the Aegean and Anatolian plate is considered to have significantly affected Miocene tectonic and magmatic evolution of the eastern Mediterranean by causing a toroidal flow of asthenosphere and a lateral gradient of extension in the upper plate. Some studies suggest that this lateral gradient is accommodated by a distributed sinistral lithospheric-scale shear zone whereas other studies favor a localized NE-SW striking transfer zone. Recent studies in the northern Dodecanese demonstrate that the transition zone between the Aegean and Anatolian plate is characterized by Miocene extension with a constant NNE-SSW sense of shear accommodating the difference in finite extension rates in the middle-lower crust. Neither localized or distributed strike-slip faults nor rotation of blocks about a vertical axis have been observed.

In this work we focus on the geology Kalymnos located in the central Dodecanese. Based on our new geological map, three major tectonic units can be distinguished: (i) Low-grade, fossil-rich late Paleozoic marbles, which have been deformed into S-vergent folds and out-of-sequence thrusts. This fold-and-thrust belt is sealed by an up to 200 m thick wildflysch-type deposit consisting of low-grade metamorphic radiolarites and conglomerates with tens of meters-scale marbles and ultramafics blocks. (ii) Above this unit, amphibolite facies schists, quartzites and amphibolites are tectonically juxtaposed along a several meter-thick thrust fault with low-grade ultramylonites and cohesive ultracataclasites/pseudotachylites with top-to-N kinematics. (iii) At highest structural levels, a major cataclastic low-angle normal fault zone localized in Verrucano-type violet slates separates Mesozoic unmetamorphosed limestones in the hanging wall. The sense of shear of the normal fault is top-to-SSW. All units are cut by brittle high-angle normal faults shaping the geomorphology of Kalymnos, which is characterized by three major NNW-SSE trending graben systems.

New white mica Ar-Ar ages suggests that the middle units represent relics of a Variscan basement, which was thrusted on top of a fold-and-thrust belt during an Eo-Cimmerian event. Zircon (U-Th)/He ages from the Variscan basement are c. 28 Ma, indicating that the lower units were exhumed below the Mesozoic carbonates during the Oligocene-Miocene. Since Miocene extension in the northern Dodecanese records top-to-NNE kinematics, we suggest that back-arc extension in the whole Aegean realm and transition to the Anatolian plate is bivergent, and tearing in the Hellenic slab did not significantly affected the extension pattern in the upper crust.

How to cite: Grasemann, B., Schneider, D. A., Soukis, K., and Roche, V.: Bivergent extension in the overriding plate above a slab tear (Dodecanese, Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3167, https://doi.org/10.5194/egusphere-egu2020-3167, 2020.

Increasing evidence suggests that large thrust-faults that splay from the plate-interface to extend within the upper-plate have a significant impact on subduction seismogenesis. The manner in which these two elements, the plate-interface itself and its splay-thrust faults, interact with one another during the earthquake cycle remains, however, poorly explored. Here, we use GPS velocities, constrained by millennial fault slip-rates, to quantify the accumulation (and partitioning) of strain on individual faults of the plate-interface zone and capture their possible interactions. We zoom into the southern Hellenic Subduction System (HSS), where the greatest (M8.3) earthquake and tsunami ever recorded in the Mediterranean was produced by slip on a splay-thrust fault. Our analysis shows that the HSS is kinematically segmented and strain is accumulated at spatially variable rates along individual structures of the plate-interface zone. We find that insterseismic locking reaches up to ~85% and ~45% on the western and eastern segments, respectively, and on structures different to those that ruptured historically. Although the western HSS has been more active recently (e.g. 365 BC), the eastern HSS carries currently higher potential for large-magnitude (M>6) earthquakes andits interface-zone appears to be closer to failure. Elastic fault-interactions are responsible for both significant inter-segment variability in strain-accumulation and millennial uniformity in earthquake rupture-segmentation between eastern and western HSS.

How to cite: Saltogianni, V., Mouslopoulou, V., Oncken, O., Nicol, A., Gianniou, M., and Mertikas, S.: Persistent earthquake-rupture segmentation due to variable interseismic slip accumulation within the southern Hellenic subduction plate-interface zone in Greece , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4857, https://doi.org/10.5194/egusphere-egu2020-4857, 2020.

Amorgos is the south-eastern outpost of the Cyclades Islands in the Aegean Sea, which forms part of the Neogene-Quaternary zone of crustal and lithospheric N-S upper plate extension northward of the Hellenic subduction zone and deep sea trench. Apart from subduction-related earthquakes further south, the southern Aegean is affected by frequent earthquakes sourced in the upper plate. The twin earthquakes of 9 July 1956, followed by a strong tsunami, were the strongest events of this kind in the past Century. Hypocenters are related to a NE-SW oriented normal fault bounding the Amorgos-Santorini Graben System. There are questions in the literature regarding the seismic source and fault plane solutions, especially the contribution of a transcurrent faulting component.

We have analyzed the kinematics of brittle faults exposed on Amorgos Island itself that could be related to Neogene and active extensional and/or transcurrent deformation. Seismic slip often occurs on previously existing faults. Thus, their orientations and kinematics may help shed light on the structure of seismic sources at depth. We present evidence for a complex history of faulting. Early normal detachment faults and shear zones overprint older (rare) reverse faults, and are themselves overprinted by several sets of dominantly dextral NE and SE trending strike slip faults. Youngest is a conjugate set of NE trending high-angle normal faults. These are especially frequent along the SE coast of the island, suggesting a clear spatial relationship with the 1956 rupture. They can be fitted to a moment tensor solution similar to the published solutions for the 1956 Amorgos earthquake. The kinematic solution for the population of early normal faults suggests that the whole of Amorgos Island may have experienced a 15° NNW tilt during later extension, which lets us suspect that the island could be a tilted block of a much larger fault system. Regarding long-term late Neogene to Quaternary kinematics, dextrally transtensive fault slip is required to fit the regional pattern of extensional deformation in the Aegean, and this is reflected by small-scale brittle faulting on Amorgos.

How to cite: Behrmann, J., Schneider, J., and Zitzow, B.: Neogene and active brittle deformation on Amorgos Island (Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10755, https://doi.org/10.5194/egusphere-egu2020-10755, 2020.

We report the mapping the co-seismic deformation in the coastal region of Durres (Albania) following the M_w=6.4 shallow earthquake on Nov. 26, 2019, 02:54 UTC. The tectonics of western and northern Albania is characterised by on-going compression due to collision between Eurasian and Adriatic plates. Crustal deformation is characterised by shortening directed at NNE-SSW to E-W orientation. We analysed co-seismic interferograms of the Sentinel-1 (ESA) satellites (ascending orbit; relative orbit 175, slice numbers 14 & 15) and GPS observations (30-s interval) recorded at two stations (DUR2 and TIR2). The raw GPS data were processed with the GIPSY-OASIS II software, using the Precise Point Positioning (PPP) methodology with Final JPL products, to obtain daily static solutions defined in ITRF14. The coseismic offsets were computed as differences between the mean positions, respectively 5 days before and after the earthquake day. Uncertainties associated with the displacements were calculated by propagating the errors in GPS solutions. For DUR2 the displacement is significant in all three components (East=-1.3 cm, North=-2.1 cm, Up= +1.4 cm), while for TIR2 seems reasonable (0.4 cm on the horizontal components) but within the error bar. The SAR images were processed by the open-source SNAP software and they were obtained on Nov. 14, 2019 20:59 UTC (master scene) and on Nov. 26, 2019 16:31 UTC (slave scene). Each frame (slice) was processed independently and the wrapped phase was mosaicked in order to reveal the full deformation extent. The InSAR fringe pattern shows a 45-km long, NW-SE arrangement of three (3) fringes with a maximum LOS displacement of about +8.4 cm near the village Hamallaj (15 km NE of Durres). Assuming a half-space elastic model with uniform slip along a rectangular fault surface, the source of the ground deformation was inverted using the available geodetic data (GNSS and InSAR). The mean scatter value between data and the model is 2.4 mm.  The inversion modelling indicates that the 2019 Durres (Albania) earthquakes ruptured a low-angle fault (24 km long by 9 km wide) dipping 23° towards east with the fault plane top at 16 km. The geodetic fault-model is in agreement with published moment tensor solutions showing a NNW-SSE fault plane (for example the USGS solution has attributes 337°/27°/91°; strike/dip-angle/rake angle). This geometry is compatible with a blind thrust fault that may root on the main basal thrust i.e. along the main Ionian thrust front that separates Adria-Apulia from Eurasia.

Acknowledgement: This research is supported by HELPOS (“Hellenic Plate Observing System” - MIS 5002697) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund). We also thank The Institute of GeoSciences, Energy, Water and Environment of Albania for providing GNSS data.

How to cite: Ganas, A., Tsironi, V., Cannavo, F., Briole, P., Elias, P., Valkaniotis, S., Koukouvelas, I., and Sokos, E.: Co-seismic deformation and preliminary fault model of the M6.4 Durres (Albania) Nov. 26, 2019 earthquake, based on space geodesy observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8478, https://doi.org/10.5194/egusphere-egu2020-8478, 2020.

The seismotectonic behavior of the Eastern Anatolia is predominantly controlled by the East Anatolian Fault (EAF). Together with the North Anatolian Fault (NAF), this ~400 km long sinistral transform fault, accommodates the westward motion of Anatolia between Anatolian and Arabian plates with a slip rate of ~10 mm/yr which is significantly slower than the motion of the NAF (25 mm/yr). Although this two major faults are similar in terms of the migration of the large earthquakes from east to west, the present seismicity of the EAF is high compared to the NAF. Except for the several earthquakes with Mw > 5, there were no devastating earthquakes during the instrumental period along the EAF. The absence of large earthquakes during the last ~50 years along the EAF indicates presence of significant seismic gaps and potential seismic hazard in the region. Recent studies indicate segmentation of the EAF with varying lengths of creeping and locked segments. Some details of the geometries and the slip rates of these segments have been estimated by the InSAR observations. Both InSAR and GPS observations indicate that the maximum creep along this the EAF is ~10 mm/yr, approximately the slip rate of the EAF.

While both geodetic data verify the existence of creep from surface deformation, its relation to the seismic behavior of the EAF is less clear. There is a ~30 km long creeping segment to the north-east of Lake Hazar which generates no significant seismicity. On the other hand, another creeping segment to the south-west of Lake Hazar, there are repeating events, below the depth of 10 km, with a horizontal extent of 15 km. The highly fractured and complex structure of this fault zone is also confirmed by the available focal mechanisms which shows significant variety.

In this study, we update seismicity catalog with improved locations to date and present a uniform and high quality focal mechanism catalog down to M4 completeness, using regional waveforms. The seismicity catalog is used to estimate the geometry of the segmentation while the novel earthquake source mechanisms are used to understand the kinematics of the segments and interactions. Moreover, we present the latest M4.9, 2019, Sivrice earthquake, pointing out a location where the stress is perturbed due to a transition from creeping segment to locked segment. (Supported by TUBITAK no: 118Y435 project)

How to cite: Guvercin, S. E., Karabulut, H., Dogan, U., Cakir, Z., Ergintav, S., Zabci, C., Ozdemir, A., Ozarpaci, S., Konca, A. O., and Kokum, M.: Present Seismotectonic Behavior of the EAF from Improved Seismicity Catalog and Earthquake Source Mechanism Solutions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18053, https://doi.org/10.5194/egusphere-egu2020-18053, 2020.

Since the 1999 Izmit-Kocaeli earthquake, the Main Marmara Fault (MMF) of the North Anatolian Fault system in the Sea of Marmara has been considered at an imminent risk for a large earthquake. Land geodesy has difficulties characterizing the distribution of interseismic loading, and hence of slip deficit, on the offshore faults, and notably on the Istanbul-Silivri segment of the NAF. The need to clarify the status of offshore fault segments has motivated seafloor monitoring experiments and marine geophysical and sedimentological studies, notably in the framework of EMSO consortium and MARSITE and MAREGAMI projects. Results from cross-disciplinary projects have shown that aseismic creep, spatially correlated to active gas venting at the seafloor, occurs on the Western segment of the MMF. This segment is also capable to large earthquake ruptures such as the 1912 event. On the eastern part of the Sea of Marmara, the Istanbul-Silivri and Prince Island segments appear essentially locked. Moreover, the base of the seismogenic zone and locking depth appears to shallow (from 15-20 to 10-15 km) from west to east.

On one hand, we propose to further evaluate fault slip rates and distribution of locking ratio on individual fault segments using an elastic block model constrained by land geodesy data and marine observations (long-term fault slip rate estimates, local acoustic ranging results). On the other hand, we evaluate the temperature at the seismogenic depths by basin modelling. Results suggest that spatial variations of fault behavior in the Sea of Marmara may result from a combination of factors. First, thermogenic gas generation within the > 6 km thick sedimentary cover in the Western Sea of Marmara may contribute to unlock the shallow part of the fault by generating overpressures. Second, heterogeneity of the crust composition could be a factor as the North Anatolian Fault system follows the intra-pontide ophiolitic suture. For instance, long term post-seismic creep onland at Ismet Paşa has been related to the presence of serpentinite in the fault zone. Moreover, high-density magnetic bodies have been identified along the MMF. Third, varying thermal regimes between the Western and Eastern parts of the Sea of Marmara may account for variations in the seismogenic depths. Seafloor heat flow in the Sea of Marmara is strongly affected by sediment blanketing and basin modeling considering this process suggests that the crustal heat flow is about 20 mW/m² higher in the eastern part than in western part of the Sea of Marmara. This difference may be explained by a more spread out crustal extension in the western Sea of Marmara.

How to cite: Henry, P., Grall, C., Özeren, M. S., Özbey, V., Uçarkus, G., Géli, L., Ballu, V., Çakir, Z., Ergintav, S., Lange, D., and Royer, J.-Y.: Contrasting seismogenic behaviors on the North Anatolian Fault in the Sea of Marmara, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10185, https://doi.org/10.5194/egusphere-egu2020-10185, 2020.

The North Anatolian Fault experienced large earthquakes with 250 to 400 years recurrence time. In the Marmara Sea region the 1999 (Mw = 7.4) and the 1912 (Mw = 7.4) earthquake ruptures bound the Central Marmara Sea fault segment. Using historical-instrumental catalogue and paleoseismic results (≃ 2000-year database), the mapped fault segments, fault kinematic and GPS data, we compute the paleoseismic-seismic moment rate and geodetic moment rate. The geodetic moment rate is obtained by projecting the measured surface displacements to estimate the strain rate, and evaluating the associated elastic stress rate over a regular spatial grid. The paleoseismic-seismic moment rate is obtained by summing the moment tensors over regions of the spatial grid and periods of time. A clear discrepancy appears between the moment rates and implies a significant delay in the seismic slip along the fault. The rich database allows us to identify the size of the seismic gap and related fault segment and estimate the moment rate deficit. Our modeling suggest that the locked Central Marmara Sea fault segment even including a creeping section bears a moment rate deficit  = 6.4*10¹⁷ N.m./yr. that corresponds to Mw ≃ 7.4 for a future earthquake with an average ≃ 3.25 m coseismic slip. Taking into account the uncertainty in the strain accumulation along the 130-km-long Central fault segment, our estimate of the seismic slip deficit being ≃ 10 mm/yr implies the size of the future earthquake ranges between Mw = 7.4 and 7.5.

How to cite: Aksoy, E., Meghraoui, M., and Toussaint, R.: The slip deficit along the North Anatolian Fault (Turkey) in the Marmara Sea: Insights from paleoseismicity, seismicity and geodetic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8809, https://doi.org/10.5194/egusphere-egu2020-8809, 2020.

The North Anatolian Fault (NAF) below the Sea of Marmara, also known as the Main Marmara Fault (MMF), has repeatedly produced major (M>7) earthquakes in the past. Currently, the MMF corresponds to a seismic gap between the locus of the most recent M>7 ruptures of the 1912 Ganos (M 7.3) and 1999 Izmit (M 7.4) earthquakes. This seismic gap has a recurrence time of approximately 250 years and has not ruptured since 1766. Consequently, it poses a major seismic hazard to the Marmara region, including the megacity Istanbul. The Marmara seismic gap is considered to be locked in the eastern and central segments of the MMF, while the western segment is partly creeping. In the context of seismic hazard and risk assessment, one of the main questions is, if either the Marmara seismic gap will rupture in a single large earthquake or in several ones due to segmentation along the MMF. In part this depends on the physical properties of the lithosphere below the Sea of Marmara as they are a key control of the contemporary stress state. To contribute to this discussion, we present 3‑D lithospheric-scale thermal and rheological models of the Sea of Marmara. These models are based on published 3‑D density models that indicate lateral and vertical crustal heterogeneities below the Sea of Marmara (Gholamrezaie et al., 2019). The density models consist of two layers of sediments, upper and lower crystalline crustal layers, and two crustal dome-shaped, high-density bodies that spatially correlate with major bends along the MMF. We show that these crustal heterogeneities may cause the lithospheric strength to vary significantly along the MMF, supporting the hypothesis that the fault is mechanically segmented. In addition, our results indicate a spatial correlation between observed aseismic fault patches (Wollin et al., 2018) and the location of the high-density bodies. These bodies are colder and stronger than the surrounding crystalline crust, and may thus represent the lateral bounds of the locked MMF segment.

How to cite: Gholamrezaie, E., Scheck-Wenderoth, M., Bott, J., Heidbach, O., Bohnhoff, M., and Strecker, M. R.: 3-D lithospheric-scale rheological model of the Sea of Marmara, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4264, https://doi.org/10.5194/egusphere-egu2020-4264, 2020.

A seismic gap along the western segment of the North Anatolian Fault, in the Marmara-Izmit region, was identified before the 1999 M7.6, Izmit and M7.4 Duzce earthquakes, so the region along the coseismic fault has been monitored with geodetic techniques for decades, providing well defined pre-, co- and post-seismic deformations. Here, we report new continuous and survey GPS measurements with near-fault (~2 – 10 km to the fault) and far-fault (~50 – 70 km from the fault) stations, including 7 years (2013 – 2019) of continuous observations, and 5 near-fault campaigns (every six months between 2014 – 2016) to further investigate postseismic deformation. GPS observations were processed with the GAMIT/GLOBK (v10.7) GNSS software. We used these observations to estimate the spatial distribution of current aseismic after-slip, along the 1999 Izmit rupture. We also searched for spatiotemporal changes of shallow creep events along the surface trace. With elastic models and GPS observations, we determined a shallow creep rate that reaches a maximum around the epicenter of the 1999 Izmit earthquake of about 12.7 ± 1.2 mm/yr, consistent with published InSAR results. Creep rates decrease both east and west of the epicentral region. Moreover, we show that broad-scale postseismic effects that diminish logarithmically, continue at present. (This study is supported by TUBITAK 1001 project no: 113Y102 and 117Y278)

How to cite: Özarpacı, S., Doğan, U., Ergintav, S., Çakır, Z., Özdemir, A., Floyd, M., and Reilinger, R.: How Has GPS Velocity Field Changed Along the 1999 Izmit Rupture 20 Years After the 1999 Izmit, Turkey Earthquake?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13052, https://doi.org/10.5194/egusphere-egu2020-13052, 2020.

Many geodetic evidence suggest aseismic slip along active faults is more common than previously thought. Furthermore, aseismic slip during the interseismic period seems to be made of intermittent slow slip events, corresponding to episodes of loading and releasing of tectonic stress over time. However, although our capabilities of detection and location of aseismic deformation have significantly increased together with the growth in available geodetic data, the physical mechanisms governing slow slip remain unknown.

We explore the spatial and temporal behavior of aseismic deformation in the vicinity of the small town of Ismetpasa, located along the central section of the North Anatolian Fault (Turkey). We combine InSAR and GNSS data acquired over the last 10 years to locate and quantify aseismic slip in the subsurface. We process SAR images (ALOS and Sentinel-1) acquired from 2007 to 2018 to build time series of ground deformation and maps of ground velocity. We confirm the presence of a 100 km-long creeping section, at rates of 10-20 mm/yr. Along this section, slip is not constant and decreases over time as formerly observed over the last 60 years. Furthermore, via a detailed analysis of our geodetic time series, we detect 3 major episodes of aseismic slip between 2015 and 2018, with durations ranging from 6 months to 1 year and magnitudes between 4.6 - 5.2. These results are compared with time series obtained from a network of GNSS permanent stations we have installed in the region (17 stations, period 2016 - 2019). As a conclusion, aseismic slip along this section of the North Anatolian Fault is characterized by slow slip events rather than by a constant, steady-state aseismic slip rate. We discuss the potential implications in terms of mechanics of slow slip along the NAF.

How to cite: Jara, J., Ozdemir, A., Benoit, A., Jolivet, R., Çakir, Z., Ergintav, S., and Dogan, U.: A geodetic exploration of the behavior of aseismic slip along the central section of the North Anatolian fault, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18112, https://doi.org/10.5194/egusphere-egu2020-18112, 2020.

The republic of Georgia is located in the Caucasus, between the Black and Caspian seas from the west and the east, and Greater and Lesser Caucasus mountains from the north and the south. Tectonically, the region belongs to the Alpine-Himalayan collisional zone, formed during the late Cenozoic period as a result of a collision between the Arabian and Eurasian plates. The deformation zone due to this collision is broad and extends from Zagros mountains in southern Iran to the Greater Caucasus in the north. The GPS studies conducted during the last decade suggest a convergence rate of 18 mm/yr between the Arabia and Eurasia plates. Although majority of this convergence occurs in the southern part of the deformation zone, important part of this convergence takes place in Georgia, implying an elevated seismic risk in the region. This is corroborated by a presence of significant historical and instrumental earthquakes in the country.

As part of the project dealing with the detection of possible low frequency electromagnetic emissions proceeding earthquakes, in summer of 2016 we have installed a continuous GNSS station MTSK between Mtskheta and Tbilisi. The station consists of Leica GRX1200 GNSS receiver with an AS10 antenna. It is mounted on top of the building, anchored to the existing brick wall. In contrast, principal convergence between the Lesser and Greater Caucasus across the Tbilisi segment, occurs along the northern boundary of the Lesser Caucasus. To constrain the velocity gradient to the northern boundary of the lesser Caucasus, in 2019 an additional continuous GNSS station MKRN was installed in this deformation zone by the GTDI near the settlement of Mukhrani. It consists of Trimble 5700 receiver with a Zephyr Geodetic antenna.

The analysis of the data is performed using the Gamit/Globk software package from MIT and it is processed in conjunction with 26 continuous GNSS stations of the GEO-CORS network operated by National Agency of Public Registry of Georgia (geocors.napr.gov.ge). In addition, we analyze data form the stations located on Eurasia, Arabia and Africa plates. The principle objective of the given work is to monitor millimeter level deformation of the crust due to the collision of Arabia and Eurasia tectonic plates and identify the regions of higher deformation and relate them to individual faults.

This work has been partially supported by Shota Rustaveli National Science Foundation of Georgia (grant DI/21/9-140/13) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) project, financed by the Spanish MINEICO. We are grateful to the Andronikashvili Institute of Physics (www.aiphysics.tsu.ge) for letting us use their facility for the installation of the GNSS station.

How to cite: Sokhadze, G., Hahubia, G., Kachakhidze, M., and Khazaradze, G.: Present-day crustal deformation of Georgia (Caucasus), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8100, https://doi.org/10.5194/egusphere-egu2020-8100, 2020.

The Eastern Turkish High Plateau (ETHP) presents one of the most critical areas of Turkish-Iranian Plateau, where active slip rates and kinematics of the faults have been used in models that aim to describe the overall deformation characteristics (such as; the beginning of the collision and convergence velocity) of the Arabian-Eurasian collision. However, lack of the spatial distribution of horizontal slip and rock uplift rates of the Bitlis-Zağros Mountain Range (BZMR) prevent our understandings about active deformation of Turkish-Iranian Plateau. Mt. Muşgüneyi that constitute the NW part of BZMR and southern margin of the ETHP is critically important because conflicting viewpoints related to the active tectonics of both the ETHP, Turkish-Iranian Plateau and Arabian-Eurasian collision zone currently being adopted in research into it. In this study, I extracted spatial distribution of the fault geometry in the Mt. Muşgüneyi and river networks from DEM, satellite images and aerial photo in order to understand faulting mechanism and measure their cumulative offsets, respectively. Geomorphic indexes (mountain-front sinuosity, valley floor width to valley height ratio, transverse topographic symmetry factor, asymmetry factor, hypsometric curve and integral) and drainage pattern analysis (channel concavity, integral analyses and knick point analyses) have been used to isolate the tectonic activity of the region. The results of this study reveal that although dozens of dextral faults accommodate the strain in the region, the 260 km length dextral Kavakbaşı Fault is the most important structure in the NW part of BZMR and it takes 60% of overall deformation. Previous studies suggest that 3–4.5 Ma is needed to account for the measured 9 km cumulative offset in this region, however, I measured c.a. 24 km cumulative horizontal offset on Kavakbaşı Fault that indicates c.a. 12 Ma needed to account for the offset. Morphometric studies point out sustaining significant uplift within the Mt. Muşgüneyi and signify the uplift rate is larger than horizontal slip rate moreover my results contradict the idea that change in the nature of the collision zone 5 ± 2 Ma ago.  Furthermore, I propose that NW part of BZMR is extremely important to understand when the modern configuration of the boundary faults of the Anatolian Scholle did form? Considering similarities between the Kavakbaşı and the Nazımiye fault, which located at c.a. 70 km south of the North Anatolian Fault Zone in the Anatolian Scholle, in terms of their ages, orientations, slip senses and cumulative offset, I suggest that they belonged to the earlier dextral deformation zone along the southern margin of the collision that sinistrally offset by the East Anatolian Fault Zone (EAFZ) about 33±3 km. This offset estimate dived by calculated long-term slip rate of the EAFZ and Na-alkali basaltic activity in the Plio-Pleistocene that emplaced at the eastern part of the Anatolian Scholle yields that age of the EAFZ is 6 Ma. This study supported by TÜBİTAK Project No:115Y684.

How to cite: Sançar, T.: Active Tectonics of the Mt. Muşgüneyi: Implications for Western Part of the Turkish Iranian Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2825, https://doi.org/10.5194/egusphere-egu2020-2825, 2020.

The North Anatolian Fault (NAF) is a 1600 km dextral transform fault accommodating the motion between Anatolia and Eurasia Plates. The segments beneath the Marmara Sea, are the only part of the NAF that did not break since the 20^thcentury. Recent studies show that this 150 km seismic gap is characterized by heterogeneous interseismic behavior and significantly high background seismicity with respect to the other parts of the NAF.

On September 24 2019, an activity started north of the Main Marmara Fault (MMF) including a M_w4.7 earthquake, which led to the Mw5.8 mainshock several days later. The 2019 M_w5.8 Silivri earthquake is the largest since 1963 M_w6.3 Cinarcik earthquake in the Marmara Sea. This sequence occurred at a location that is immediate north west of the Central Basin; between a zone that is possibly partially creeping (Central Basin) to the west and a possibly locked segment to the east (Kumburgaz Basin).

 In this study we used template search for detection of earthquakes, relocated the earthquakes, obtained focal mechanism solutions of earthquakes that are M>4 and obtained a finite-fault slip model of the M_w5.8 mainshock. Using template cross-correlation, a total of 400 earthquakes were detected in this sequence. The activity started in a relatively narrow zone and spread to larger distances following the M_w4.7 mainshock. The depth distribution shows that the earthquakes are confined to a narrow zone between the depths of 9-13 km. The focal mechanisms show that there are two clusters; the cluster to the northwest show a ~70°north dipping fault with rake angles about ~160°, while the activity toward east converges to the Main Marmara Fault and dip angle is close to ~70°with rake angles of ~140°. The finite-fault model shows a bilateral rupture that propagated down-dip from the hypocenter.

We conclude that the seismic activity occurred on a fault that is within the Main Marmara Shear Zone beneath the sedimentary basin. This secondary fault possibly connects to the Main Marmara Fault to the east. There is no evidence that the causative fault continues up-dip into the basin.  Another characteristic of this sequence is that all of the focal mechanisms show significant thrust component in addition to the expected right-lateral motion. The January 2020 M_w4.7 earthquake that occurred in the same zone  between the two clusters have predominantly thrust mechanism, confirming that this zone is under local compression. The observed thrust component is possibly related to change of the width of the shear zone with narrowing from Central Basin to the west to Central High to the east and/or the change of the interseismic behavior of the fault from partially creeping Central Basin and locked Kumburgaz Basin segments.

How to cite: Konca, A. O., Guvercin, S. E., Karabulut, H., Eskikoy, F., and Ergintav, S.: 2019 Mw5.8 Silivri Earthquake Reveals the Complexity of the Main Marmara Shear Zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8438, https://doi.org/10.5194/egusphere-egu2020-8438, 2020.

Geodetic measurements of crustal deformation rates can provide important constraints on a region’s earthquake hazard that purely seismicity-based hazard models may miss. For example, geodesy might show that strain (or a deficit of seismic moment) is accumulating faster than the total rate at which known earthquakes have released it, implying that the long-term hazard may include larger earthquakes with long recurrence intervals (and/or temporal increases in seismicity rates). Conversely, the moment release rate in recent earthquakes might surpass the geodetic moment buildup rate, suggesting that the long-term-average earthquake activity and hazard may in fact may be more quiescent than might be estimated using the earthquake history alone. Such geodetic constraints, however, have traditionally been limited by poor spatial and/or temporal sampling, resulting in ambiguities about how the lithosphere accommodates strain in space and time that can bias estimates of the resulting hazard. High-resolution deformation maps address this limitation by imaging (rather than presuming and/or modelling) where and how deformation takes place. These maps are now within reach for the Alpine-Himalayan Belt – one of the most populous and seismically hazardous regions on Earth – thanks to the COMET-LiCSAR InSAR processing system, which performs large-scale automated processing and timeseries analysis of Sentinel-1 data provided by the EU’s Copernicus programme. We are pairing LiCSAR products with GNSS data to generate high-resolution maps of interseismic surface motion (velocity) and strain rate for the Anatolia region. Here we quantitively investigate what these strain rate distributions imply for seismic hazard in this region, using two approaches in parallel.

First, building on previous work, we develop a fully probability-based method to pair geodesy and seismic catalogs to estimate the recurrence times of large, moderate and small earthquakes in a given region. We assume that earthquakes 1) obey a power-law magnitude-frequency distribution up to a maximum magnitude and 2) collectively release seismic moment at the same rate that we estimate it is accumulating from the strain rate maps. Iterating over various magnitude-frequency distributions and their governing parameters, and formally incorporating uncertainties in moment buildup rate and the magnitudes of recorded earthquakes, we build a probabilistic long-term-average earthquake model for Anatolia as a whole, including the most likely maximum earthquake magnitude. Second, we estimate how seismic hazard may vary from place to place within Anatolia. Using insights from dislocation models, we identify two key signatures of a locked fault in a strain rate field, allowing us to convert the newly developed strain maps to “effective fault maps.” Additionally, we explore how characteristics of earthquake magnitude-frequency distributions may scale with the rate of strain (or moment) buildup, and what these scaling relations imply for the distribution of hazard in Anatolia, using the seismic catalog to evaluate these hypotheses. We also explore the implications of our findings for seismic hazard and address how to expand these approaches to the Alpine-Himalaya Belt as a whole.

How to cite: Rollins, C., Wright, T., Weiss, J., Hooper, A., and Walters, R.: Converting InSAR- and GNSS-derived strain rate maps into earthquake hazard models for Anatolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6144, https://doi.org/10.5194/egusphere-egu2020-6144, 2020.

Based on >20 years of GPS observations and seismological works, direct constraints on the strain accumulation along the Main Marmara Fault (MMF) show different characteristics from Princess Islands to Ganos Fault. Ganos and Princess Island segments identified as locked based on GPS and seismological observations while the part of the Central Marmara segment show partially creeping behaviour. Moreover, around the Kumburgaz Basin, GPS data could be explained by creep models in contrast to fully locked seismic models. Clearly, there are many puzzling questions on the nature of strain accumulation on the MMF, under the constrain of various data sets. In order to contribute to a better understanding of this fault the observation capacity of geodesic network has been increased along the northern coast of the Marmara Sea and supported by seismological stations as well as Marine Geodesy.

In September, 2019, an intense earthquake activity started between Central Marmara and Kumburgaz Basin. The mainshock occurred on 26 September 2019 (Mw5.8) as a largest earthquake, since 1963 Mw6.3 Cinarcik earthquake, in the Marmara Sea. A foreshock activity started 4 days before the mainshock and the largest one (Mw4.7) observed on September 24, close to the mainshock. The mechanisms of the mainshock and the large aftershocks as well as foreshocks are dominantly strike-slip with a significant reverse component. The aftershocks are located on the north of the MMF trace.

Here we investigate the geodetic data related to this event, with the aim to shed some light on the complexly segmented MMF. We observed co-seismic offsets at the nearest 6 GPS stations (~12-20 km far to the epicenter) along the northern coastline of the Sea of Marmara.  The estimated offsets are not big and change between 1-3 mm on horizontal and 1-10 mm on vertical components.  All of the stations are located on the northern part of the hypocenter and exhibit predominant NS-direction movement, which is inconsistent with a primarily E-W right lateral transform system. Instead, the co-seismic pattern can be explained with a complex earthquake mechanism which has a dominant reverse component while the strike-slip component is relatively insignificant, based on Okada-type elastic models and geodetic moment magnitude obtained as ~6.2. The total cumulative moment using geodesy is much higher than the total seismic cumulative moment of earthquake activity (~M5.9), and the thrust component is also more dominant in comparison the focal mechanisms from regional data. Obviously, geodetic co-seismic offsets estimated from daily-based data and they include pre-and post-earthquake deformations. In addition, the tide-gauge data (station distance is 25 km far to epicenter) was analyzed and it shows the strong variations after Mw 4.7 and they faded out after Mw5.8. This sea level change, which temporally correlates with the seismic activity,  gives important evidence about the possibilities of pre-earthquake activity. Using GPS time series, we intend to explore the pre-earthquake anomalies and, to reduce the discrepancy between seismological and geodetic models. (This study is supported by TUBITAK 1001 Project no: 117Y278).

How to cite: Ergintav, S., Ödemir, A., Özarpacı, S., Erkoç, H., Ayruk, E. T., Doğan, U., Karabulut, H., Konca, A. Ö., Walter, T., and Vasyura-Bathke, H.: Analysis of the complexity of the Mw 5.8, 26 September 2019 Silivri Eq. in the Sea of Marmara, Turkey, constrained from geodetic datasets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17589, https://doi.org/10.5194/egusphere-egu2020-17589, 2020.

The Aegean Sea region sits in a complex deformation zone between the African, Eurasian, and Anatolian plates. It contains the Hellenic subduction zone, where African oceanic lithosphere descends under the Aegean Sea. The subducting slab may be torn or fragmented at both its eastern (Pliny-Strabo zone) and western (Kefalonia fault) edges. The overriding Aegean Sea is cut by numerous active normal faults accommodating north-south extension. On top of this, the collision of Arabia with Anatolia farther east drives Anatolia and the connected Aegean Sea westward, resulting in the left lateral North Anatolian fault (and its extension into the Aegean), as well as greater relative velocities between the subducting slab and the overriding plate. These geodynamic processes and geological features all affect the present-day kinematics of the Aegean region.

Surface velocities measured at Global Navigation Satellite System stations throughout the Aegean provide important constraints on these underlying geodynamic forces. Previous studies have attributed the surface motions to some combination of plate boundary interactions, lateral variations in gravitational potential energy (GPE), subduction and slab tearing, internal faulting, and mantle tractions. The expected imprint of these processes also varies with the rheology of the lithosphere. Up to this point, there has been little effort to systematically evaluate the relative contributions of these different forces. In this study, we implement a Markov Chain Monte Carlo approach to efficiently and precisely determine the likely values and uncertainties of these geodynamic forces and the lithospheric rheology. We also identify trade-offs between processes that produce similar surface signals.

Preliminary results indicate that the dominant imprint on surface velocities comes from the southwestward rollback of the Hellenic slab and the westward escape of Anatolia. Although lateral variations in GPE also have an effect on the velocities, these are generally less important than slab rollback and Anatolian escape. At a lithospheric scale, the North Anatolian fault has little shear resistance to allow a relatively sharp velocity transition across it. Including resistive tractions on intraplate faults within the Aegean Sea has a smaller effect on the modeled velocity field. By using the velocity field to guide a statistical analysis of the geodynamic drivers, we have been able to better constrain the primary drivers of deformation in the eastern Mediterranean.

How to cite: Herman, M., Govers, R., van de Wiel, L., and Nijholt, N.: Probabilistic constraints on lithospheric forces, fault tractions, and rheology in the eastern Mediterranean region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18364, https://doi.org/10.5194/egusphere-egu2020-18364, 2020.

The North Anatolian Fault (NAF) produced multiple earthquakes of M>7 throughout the 20th century, while the part of NAF beneath Sea of Marmara did not rupture during this period. Analysis of the Main Marmara Fault's interseismic behavior, the most active branch of the North Anatolian Fault in this region, in terms of locking depth and fault slip rate is critical for evaluating the region's seismic risk with a population of more than 20 million, as it provides information about the seismic moment deficit that may release in a potential future earthquake.

In this study, we modeled the Main Marmara Fault's interseismic locking with realistic geometry and 3D structure including sedimentary basins, by implementing a 3D finite element approach and using interseismic GPS velocities. We have optimized the fits with GPS data by evaluating cases where each fault segment is constrained by a fault slip rate below a predefined locking depth ranging from 0 to 20 km. Preliminary models reveal that a difference in locking depth is required between the Western Marmara and the eastern end of the Ganos Segment entering the Sea of Marmara. This result, which is consistent with seismicity studies and other previous studies using 1D profiles shows that the strain accumulation under Western Marmara is less and that the locking depths or couplings are not similar in these two segments. For the Princes' Islands Segment, further analysis is required due to complexity in the GPS data. Recent earthquakes along Silivri also indicate that the strain accumulation is complex with most mechanisms showing significant thrust component. We have also calculated various possible strain accumulation patterns and compared the strain rate field around the Main Marmara Fault. Our results show that in most cases the change in the seismicity of each segment is consistent with the interseismic behavior associated with its fault locking.

(This research has been supported by Boğaziçi University Scientific Research Projects Coordination Unit. Project Number: 15022, 2019)

How to cite: Yılmaz, Z., Konca, A. Ö., and Ergintav, S.: Locking Behavior of Main Marmara Fault in Western Turkey During Interseismic Period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10682, https://doi.org/10.5194/egusphere-egu2020-10682, 2020.

Harash Fayez¹, Chao Chen^1,2, Qing Liang^1,2, Chenming Tu¹

¹Institute of Geophysics & Geomatics, China University of Geosciences, Wuhan 430074, P.R. China (Corresponding  author:  Harash Fayez).

²Subsurface Multi-Scale Imaging Lab, Institute of Geophysics & Geomatics, China University of Geosciences,

 Wuhan 430074, P.R. China.

Summary

A 3-D density structure of the lithosphere and upper-mantle beneath the Mediterranean Sea and adjacent region was constructed based on inversion of gravity anomaly constrained by seismic tomography model. In this study, we have removed the terrain and crustal effects from the observed gravity field (EIGEN-6C4), in order to obtain the mantle gravity anomaly which was used to investigate the lithospheric and the upper-mantle density distribution. The 3-D inversion process is constrained by a reference density model estimated from shear-wave velocity model (SL2013sv). Our result shows some characteristics of density distribution in the lithosphere and upper-mantle that might be related to the tectonic signification beneath the Mediterranean Sea and adjacent region. A low-density zone dominates the lithosphere beneath the Mediterranean Sea except the area around Arabia shield and North Anatolian fault belt. A thinner high-density layer appears beneath the southwest of Mediterranean Sea, and it may be related to the older oceanic lithosphere fragments. The high-density anomalies appear below depth of 280 km beneath the Mediterranean Sea and the Turkish Aegean Sea Plate. However, the low-density anomalies appears at the top of the upper-mantle beneath trenches of the southwestern of Mediterranean Sea, the eastern of Aegean Sea, the Red Sea, the Black Sea and the middle of Arabia shield. It may indicate the intensity and origination of tectonic movement referring the deep structure below the Eratosthenes seamount in the Mediterranean Sea. Furthermore, the convergence region of two low-density anomaly zones may be interpreted as a significant tectonic unit.

How to cite: Harash, F.: 3-D density structure of the upper-mantle from gravity inversion constrained by seismic velocity model: A case study of the Mediterranean Sea and surrounding region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4639, https://doi.org/10.5194/egusphere-egu2020-4639, 2020.

The Marmara region is one of the most active tectonic regions with its high population and rapid but irregularly growing cities in Turkey. Located in this active zone, Istanbul has always been under the danger of being hit by destructive earthquakes, which in the past have caused serious damage in the city more than once. Major earthquakes to affect Istanbul during the Ottoman period took place in 1509, 1766 and 1894. As the latest one, we have relatively rich knowledge about the 10 July 1894 earthquake. The 1894 earthquake resulted in 474 losses of life and 482 injuries.  Around 21,000 dwellings were damaged, which is a number that corresponds to 1/7 of the total dwellings of the city at that time. Without any doubt the exact loss of life was higher. Because of the censorship the exact loss numbers remained unknown. Researchers have been split in opinion about the intensity, epicenter, magnitude, and rupture length of this event. The main target of this study is to have a better insight on the possible location of the 1894 earthquake with the help of damage analysis and ground motion modeling. Ottoman Empire archive records, scientific reports and papers, newspapers, government correspondence, letters, notes of voyagers and diaries are the major sources to make an evaluation on the type and extent of damage. An intensity map associated with the 1894 earthquake is prepared based on macro-seismic information, and damage analysis and classification. Various information types contained in the old city maps, municipal boundaries, and the population information have contributed to this assessment. Obtained damage information is presented, evaluated and interpreted.  For earthquake modelling the ELER (Earthquake Loss Assessment Routine) software is used. Using the ground motion module of ELER, several scenarios are modeled having different source, path, and site parameters. The resulting ground motion distributions are compared with the damage and intensity maps to provide a first-order assessment of the earthquake source parameters of the 1894 earthquake.

How to cite: Yenihayat, N., Çakti, E., and Şeşetyan, K.: Constraining Source Properties of the 1894 Istanbul Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22071, https://doi.org/10.5194/egusphere-egu2020-22071, 2020.

Knowledge of the present-day relationships between earthquakes, active tectonics, and crustal deformation is a key for understanding the geodynamics, ongoing surface processes (i.e. erosion, sedimentation, etc.) and is also essential for the risk assessment and management of geo-reservoirs for energy and waste.

Greece is characterized by the most tectonically active regime in the eastern Mediterranean, involving (a) intense crustal deformation and thickening, with an uplift rate of a few mm/yr along the Hellenic Arc due to accretion of sediments of the African plate beneath the overriding Aegean plate, (b) wide-spread extension in the back-arc region (for example in the Gulf of Corinth) due to retreat of the African slab and (c) significant strike-slip motions due to offset between oceanic-continental subduction in the west and the westward propagation of Anatolia in the east. Study of the complexity of the contemporary Greek tectonics has been the subject of intense efforts of our working group during the last decade, employing multidisciplinary state-of-the-art methodologies regarding geological mapping, seismological and geodetic surveying and numerical analyses at various scales. The products of these studies are the pieces of a puzzle that we aim to merge with existing data (topography, bathymetry, land-use, etc) in order to compose the digital version of the modern Seismotectonic Atlas of Greece.

It has been over 30 years since the first edition of the seismotectonic map was published by Greece's Geological Institute in 1989, which emerges the need for an update, as soon as dozens of strong earthquakes have occurred both on mainland and offshore, whose locations and fault kinematics have been studied and this information has to be taken into account in city and infrastructure planning. Moreover, the patterns of active tectonics and stress, the tectonic strain distribution, the annual ratio between seismic and geodetic moment release, the precise location of onshore active faults and the slip-rates of major faults are much better known today than they were 30 years ago.

Open-source mapping software and GIS tools are being used to showcase important up-to-date seismotectonic features together with critical geospatial information (motorways, railways, gas pipelines, electricity plants, etc) at a nationwide scale of 1:500,000. This updated product aims to reveal a comprehensive image of the regional crustal deformation in a useful manner for scientists, students, and stakeholders to obtain a first-order perception of seismic risk in the Greek territory, but, also, to be used as a basis for other applications in Geosciences.

How to cite: Kassaras, I., Kapetanidis, V., Ganas, A., Tzanis, A., Papadimitriou, P., Kouskouna, V., Karakonstantis, A., Valkaniotis, S., Chailas, S., Sakkas, V., Kosma, C., Bozionelos, G., Tsironi, V., and Giannaraki, G.: Design and implementation of the seismotectonic Atlas of Greece v1.0, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2220, https://doi.org/10.5194/egusphere-egu2020-2220, 2020.

A massive template-matching approach is successfully applied in Marmara Sea region along  the North Anatolian Fault, during the 2009-2014 period to enrich the description of the time and space evolution of the seismicity. Detection of events are performed on the continuous data recorded from 2009 to 2014 combining two types of catalogs as templates: a finely constructed catalog for the three first year (2009-2011) (Schmittbuhl et al, 2016) and a raw catalog from KOERI for the last three years (2012-2014).  Magnitudes (Ml) are estimated for all detected events using relative amplitudes of the highly coherent waveforms between new events and template events. The template database provides a nearly threefold increase of the number of small events (more than 15000 earthquakes compare to the 4673 events of the initial catalog). Combined with a double-difference relocation based on cross-correlation differential travel-time data, the database is shown to be a relevant framework for the long term monitoring of specific remanent structures like seismic swarms or repeating earthquakes. The obtained catalog confirms the strong contrast of behaviors along the Main Marmara Fault (MMF): deep creeping to the west (Central Basin), fully locked in the center (Kumburgaz Basin) and dominated by fluid and off-fault activity to the east (Cinarcik Basin).

How to cite: Karabulut, H., Lengliné, O., Schmittbuhl, J., Matrullo, E., and Bouchon, M.: High resolution seismicity catalog of the Marmara Sea region during the 2009-2014 period using template matching, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15127, https://doi.org/10.5194/egusphere-egu2020-15127, 2020.

Southern Aegean is the major part of the Eurasian plate overriding the subduction of African plate in eastern Mediterranean region. In this study, shallow depth (< 40 km) events recorded by temporary and permanent seismic networks in southern Aegean are used to study the crustal scattering attenuation (Q_s^-1) and intrinsic attenuation (Q_i^-1) of S-waves. The 3 component S-waveforms are filtered in 1-2, 2-4, 4-8, and 8-16 Hz bands and envelopes are calculated by smoothing the root mean square of individual components. The envelopes are modeled using the approximate analytical solution of 3D isotropic radiative transfer equation. The fitting is performed using grid search approach to obtain Q_s^-1 and then linear inversion is used to calculate Q_i^-1 for each source station pair. The results obtained from each source-station pair are assigned to an ellipsoid region and robust mean technique is used to map the results in each 0.20^o x 0.20^o bin. The final results indicate consistently high Q_s^-1 in western Crete in all 4 frequency bands. Also, high Q_s^-1 is observed in western Peloponnese in 1-2 and 2-4 Hz frequency bands. High Q_i^-1 is observed along the volcanic arc in all 4 frequency bands. Our results compare well with the recent S-wave scattering study in the region. They are also consistent with the geodynamics of southern Aegean subduction zone. Our study provides useful insight about the attenuation in the southern Aegean crust which has implications for ground motion and seismic hazard.

How to cite: Ranjan, P. and Konstantinou, K. I.: Crustal scattering and intrinsic attenuation of S-waves in southern Aegean derived using envelope inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4668, https://doi.org/10.5194/egusphere-egu2020-4668, 2020.

The interseismic slip distribution in the Marmara fault system represents both observational and modelling challenges. The observational challenge is obvious: the faults are under water and to understand their interseismic behavior (creeping versus locked) requires expensive and logistically difficult underwater geodetic measurements, alongside those on land. Up to now, two such underwater studies have been conducted and they suggest that the segment to the south of Istanbul zone (so-called Central segment) is locked while some creep is probably going on along the neighboring segment to the west. Given these two important findings, the slip distribution problem is still non-trivial due to the fact that our experiments so far demonstrate that the block-based slip inversions and those that only consider a single fault (with the same geometry as one of the boundaries of the blocks) give significantly different results. In this study we approach the problem using three methodologies: block models with spatially non-varying strains within individual blocks, a boundary element approach and a continuum kinematic approach. Although the block model does not give spatially varying strains, the inversion results from the block model can be used as an input to model strain field in the vicinity of the fault. We constract a formulation to correlate the results from these with the strain rates obtained using focal mechanism summations.

GPS velocities are taken from previous studies around the Marmara Sea such as Reilinger et al., (2006), Aktuğ et al., (2009), Ergintav et al., (2014), Özdemir et al., (2016) and Özdemir and Karslıoğlu, (2019). Since all studies have different processing strategies or by choosing different reference frames, the GPS velocity fields could not be combined directly. Hence, we combined all velocity fields by minimizing the residuals between the velocities of the common sites in the studies. For this purpose VELROT program (Herring et al 2015) was used. Reilinger et al., (2006) was selected the reference field and other velocity fields were aligned one by one on it. If the combined sigma of the pairs of velocity estimates in the residuals are greater than 2 mm yr^-1, that sites are excluded from the final velocity field. As a result, 127 GPS velocities were used in the developed models.

How to cite: Özbey, V., Özeren, M. S., Henry, P., Klein, E., Galgana, G., Lange, D., Royer, J.-Y., Ballu, V., and Çakır, Z.: Three Approaches to Interseismic Slip Rates on the Marmara Faults and Their Tensorial Correlations with the Kostrov-Based Strain Rates , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20421, https://doi.org/10.5194/egusphere-egu2020-20421, 2020.

The Santorini-Amorgos zone represents right-lateral transtensional regime from NE of Santorini to the south of Amorgos which also hosts Kolumbo submarine volcano. A total number of 1869 crustal events from 2002 to 2019 were recorded by permanent and temporal seismic networks deployed in southern Aegean. Absolute locations of these events were obtained by utilizing the probabilistic nonlinear algorithm NonLinLoc. Precise relative relocation by using double-difference algorithm with catalog and cross-correlation differential times was later performed, resulting in 1455 locations with horizontal and vertical uncertainties of less than 0.3 km. Clusters of earthquakes relocated between Naxos and Paros as well as north of Astypalaia do not coincide with any fault in the area. Similarly, the relocated crustal events across Santorini-Amorgos zone show that most of the earthquake clusters do not coincide with any of the existing faults. The distribution of Vp/Vs ratios in the area were investigated based on the P and S-wave travel times of all the events. Vp/Vs ratios in the area vary between 1.67 and 2.03 with errors less than 0.04. The highest Vp/Vs values were found to be distributed in the area between Naxos and Paros. Other areas with notably high Vp/Vs ratio are north of Santorini, Anydros, west of Amorgos, offshore area south of the easternmost tip of Amorgos, and the island of Astypalaia. These mentioned areas were also rich in seismic activities during the period of study. The high Vp/Vs ratios in the region of high seismicity signifies that these events were likely related to the migration of magmatic fluids to the surface and may not be caused by the existing faults.

How to cite: Andinisari, R., Konstantinou, K. I., Ranjan, P., and Hermawan, Q. F.: Seismotectonic setting of Santorini-Amorgos zone and the surrounding area revealed from crustal earthquakes relocation and Vp/Vs distribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6589, https://doi.org/10.5194/egusphere-egu2020-6589, 2020.

This study focuses on the crust of the Eastern Marmara in order to understand of how much the structure is influenced by the tectonic history and also by the activity of the NAF. Recent studies have claimed that the crustal thickness varies significantly on the north and south of the NAF, which is assumed to indicate the separation line between Eurasian and Anatolian Plates. The present study aims to reevaluate the claim above, using newly available data and recently developed tools. The methods used during the study are the receiver function analysis and surface wave analysis. The first one is more intensively applied, since the second one only serves to introduce stability constraint in the inversions. Data are obtained from the permanent network of KOERI and from PIRES arrays.  The main result of the study indicates that the receiver functions for the stations close to the fault zone are essentially very different from the rest and should be treated separately. They show signs of complex 3D structures of which two were successfully analyzed by forward modeling (HRTX and ADVT). A dipping shallow layer is seen to satisfy the major part of the azimuthal variation at these two stations. For the stations off the fault on the other hand, the receiver functions show a more stable behavior and are analyzed successfully by classical methods. CCP stacking, H-k estimation, single and joint inversion with surface waves, are used for that purpose. The results obtained from these totally independent approaches are remarkably consistent with each other. It is observed that the crustal thickness does not vary significantly neither in the NS, nor in the SW direction. A deeper Moho can only be expected on two most NE stations where a gradual transition is more likely than a sharp boundary (SILT and KLYT). The structural trends, although not significant, are generally aligned in the EW direction.  In particular, a slower lower crust is observed in the southern stations, which is possibly linked to the mantle upwelling and thermal transient of the Aegean extension. Otherwise neither the velocity, nor the thickness of the crust does not imply any significant variation across the fault zone, as was previously claimed.

How to cite: Büyükakpınar, P. and Aktar, M.: The Crustal Structure of the Eastern Marmara Region Using Receiver Function Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4689, https://doi.org/10.5194/egusphere-egu2020-4689, 2020.

Located on the Hellenic Volcanic Arc, the Christiana-Santorini-Kolumbo (CSK) marine volcanic zone is notorious for its catastrophic volcanic eruptions, earthquakes and tsunamis. Here, not only the largest volcanic eruption in human history, the so-called “Minoan” eruption took place in the Late Bronze age 3600 years ago, but also the largest 20th-century shallow earthquake in Europe of magnitude 7.4 in 1956. Although the region is heavily populated and a fully developed touristic region, the acting tectonic forces are not fully understood to this day aggravating the necessary assessment of geohazards.

Recent bathymetric and seismic studies revealed that the CSK zone comprises a system of neotectonic horst and graben structures with extended internal faulting that is thought to be the result of the ongoing extension in the southern Aegean. The NE-SW alignment of volcanic edifices within the CSK underlines the tectonic control of volcanism in this area. In this study, we show how advanced reprocessing of selected seismic lines leads to significantly improved seismic images revealing new details of the complex rift system. Moreover, using a unique diffraction-based approach for velocity model building, we perform pre-stack depth migration (PSDM) and present for the first time depth-converted seismic sections from the CSK zone. This allows for the proper estimation of fault angles, sedimentary thicknesses and performing structural restoration in order to reconstruct and measure the amount of extension in the individual rift basins. We revise the previous seismostratigraphic scheme and propose a new correlation between the horst and graben units.

Structural restoration indicates an extension of approx. 3 km along the Santorini-Anafi basin while PSDM indicates the sedimentary strata to be of maximum 1500 m thickness. According to the new stratigraphic model, we infer a four-stage evolution of this basin in which early marine deposition, syn-rift deposition, complex infill deposition and neotectonic syn-rift deposition are distinguished. Moreover, we identify negative flower structures within the basin centre indicating the presence of a strike-slip component, which superimposes the dominant NW-SE directed extension. Based on these findings, we are confident that by applying the proposed workflow to the complete regional dataset, the understanding of the relationship between tectonics and volcanism in the CSK zone will be significantly improved, and, consequently, will lead to an improved risk assessment of the central Aegean Sea.

How to cite: Huebscher, C. and Preine, J.: Reprocessing, depth conversion and structural restoration of vintage seismic data: New insights into the volcano-tectonic evolution of the Christiana-Santorini-Kolumbo marine volcanic zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5418, https://doi.org/10.5194/egusphere-egu2020-5418, 2020.

Twenty six years after the Mw 7.3 Gerede Earthquake in1944, Ambraseys (1970) first recognized, in the offset of a manmade wall, the signature of slow aseismic slip along the central segment of the North Anatolian Fault (NAF). Following this discovery, many studies characterized the behavior of aseismic slip with land-and space-based geodetic techniques, including creepmeters. It is now well recognized that the aseismic slip rate decreases logarithmically from more than 3 cm/yr in the years following the Gerede Earthquake to approximately 6±2 mm/yr today. In the last two decades, InSAR allowed deriving maps of ground velocities suggesting that aseismic slip extends along a 100-km-long section of the fault. Furthermore, aseismic slip rate varies in space along strike, reaching its peak value approximately 15-24 km east of the city of Ismetpasa. Furthermore, creepmeter measurements and InSAR time series indicate that aseismic slip in the region of Ismetpasa behaves episodically rather than continuously, alternating quiescent periods and transient episodes of relatively rapid aseismic slip. These observations raise questions about how slip accommodates tectonic stress along the fault with significant implications in terms of hazard along the seismogenic zone.

In order to monitore spatial and temporal variations in the aseismic slip rate and to detect slow slip events along the fault, we have established ISMENET -Ismetpasa Continuous GNSS Network- in July 2016. ISMENET stations are distributed over approximately 120 km along strike. In order to explore the shallow, fine spatio-temporal behavior of aseismic slip, stations are located within 200 m to 10 km of the fault. We process GNSS data with the Bernese (V5.2) and GAMIT/GLOBK (V10.7) GNSS software. We analyze the GNSS time series to extract the signature of aseismic slip using a principal component analysis to reduce the influence of non-tectonic noises.

Keywords: Ismetpasa, Aseismic slip, GNSS, PCA, Time Series Analysis, NAFZ

How to cite: Özdemir, A., Doğan, U., Jara, J., Çakır, Z., Jolivet, R., Ergintav, S., Özarpacı, S., and Benoit, A.: Detecting Transient Creep Events on the Ismetpasa Segment of the North Anatolian Fault with Continous GNSS Time Series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11174, https://doi.org/10.5194/egusphere-egu2020-11174, 2020.

The slab edge processes related to the subduction of the African slab along the Aegean-Cyprian trench, beneath Anatolia, played a significant role in Cenozoic extension in western Anatolia. The Datça Basin, which includes various Late Miocene depositional environments characterised by continental to marine transitions, is a WSW-ESE trending asymmetric depression developed on the Datça Peninsula, which separates the Aegean and Eastern Mediterranean Seas at the SW corner of Anatolia. Presently, the region is seismically active and is dominated by the E-W-trending Gökova Graben in the north and the NE-SW-trending Pliny-Strabo Trench in the south. Here, we conduct high resolution integrated stratigraphic study, that includes biostratigraphy, magnetostratigraphy as well as kinematic studies involving paleostress analysis to unravel geodynamic evolution of the region within the context of Africa-Eurasia convergence.  

Three prominent sequences separated by unconformities are recognised in the  Datça Basin; i) facies associations related to alluvial fan to fluvio-lacustrine deposits of Pliocene age, ii) facies extending from alluvial fan to fluvio-deltaic to marine incursions interlayered with two air-fall ash deposits of Pleistocene age, and iii) alluvial fan to fluvial to marine coastal facies of the modern basin infill. Integration of available information and our findings indicate that the basin experienced three distinct deformation phases associated with reactivation of pre-existing structures since Pliocene. First, the Datça Basin was initially developed as a transtensional basin in Pliocene possibly due to strike-slip deformation related to the Pliny-Strabo Trench, then orthogonal extensional deformation dominated and the basin evolved into a superimposed half-graben as a result of NNE to NNW directed extensional strain and subsequently became a full graben under N-S directed extension by the late Pliocene onwards.  

This research is supported by The Scientific and Technological Research Council of Turkey (TUBITAK) with Grant Number of 117R012.

Keywords: Integrated stratigraphy, kinematics, basin evolution, Datça Basin, Southwestern Anatolia

How to cite: Sümer, Ö., Şiş, F. S., İnce, M. D., Özkaymak, Ç., Tosun, L., Uzel, B., Stoica, M., Langereis, C., and Kaymakci, N.: Geodynamic Evolution of Datça Basin Since the Pliocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4070, https://doi.org/10.5194/egusphere-egu2020-4070, 2020.

The study area (40-40.45°N and 30-32.15° E) exhibits a high topography (1200-1800 m elevation) and bounded by the Galatean Massif at east, Pontide Mountain Range to the north, the Central Anatolian Plateau to the south and the Marmara Sea to the west. The region is actively been deformed and dissected by the active branches of the dextral strike slip North Anatolian Fault Zone (NAFZ) and the Sakarya River (SR) system. We have investigated the depositional terraces formed along the main course and the major tributaries of the SR to reveal the dynamics of the terrace formation by climate, sea level changes and also to quantify the variations in rate of vertical deformation within the current geodynamics of the NW Anatolian Block. The geometry of the main river (1) and its tributaries (4) allow us to determine the spatio-temporal variations in four vertical (100 km) and three along fault sections (200 km) since the last ~150 ka.

Up to date, we have mapped 23 distinct evenly scattered multi-step terrace staircases along the main river course and its 6 major tributaries. Mapping is aided with high precision rtk-GPS profiling and SfM photogrammetry using UAV. The dating is carried by luminescence geochronology (OSL and p-IRIR) to constrain the timing of the formation and also abandonment of each depositional terrace step.

The results show that the focus region is under control of vertical deformation at a rate of 0.6-0.7 mm/year regardless from the distance to the main strand of the NAFZ. There is also evidence that this rate has been decelerated from ~1.0-1.1 mm/year since the last 100 ka. The distinct variations in the calculated uplift rates along the profiles reveal apperant southwards tilting in between the active branches of the NAFZ and also within the block.

This study is funded by TUBITAK 117Y426 project grant. 

How to cite: Erturac, M. K., Şahiner, E., Sağlam Selçuk, A., Gürbüz, A., Okur, H., Zabcı, C., Meriç, N., Özeren, S., and Sunal, G.: Spatio-temporal variations on the vertical deformation rate of the NW Anatolian Block: Luminescence chronology of the Sakarya River terraces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6168, https://doi.org/10.5194/egusphere-egu2020-6168, 2020.

Southwestern Anatolia is part of a N-S extensional regime mainly driven by rollback along the Hellenic subduction zone beneath the Aegean Sea. This seismically active area is controlled primarily by normal fault systems. The fault structures in the region are segmented and in many cases seismic interaction between these segments can be observed.

2017 seismic activity along the Eastern and Western edges of Gökova Bay. Within the same year, three separate moderate sized (Mw~5) events took place near the town of Ula (Muğla) on the eastern edge of Gökova Bay. One of these earthquakes occurred in April before the Bodrum-Kos earthquake while the other pair occurred in November within two days.

We relocated all the events that occurred in Ula region in 2017 and remodeled the source mechanisms from regional seismic waveforms by using Bayesian Earthquake Analysis Tool (BEAT). The surface deformations can also be clearly observed from InSAR tracks of both ascending and descending orbits. Because of the large noise margins of the interferograms, atmospheric noise corrections and high resolution DEM data were used.

Due to temporal and spatial proximity of the two Mw~5 events during the November sequence, InSAR yields only cumulative deformation of the earthquakes. Therefore, we determined the contribution of each event to the cumulative static displacements observed by InSAR data, using the source models from seismic waveforms. The locations and the source mechanisms of the two Mw~5 earthquake are consistent and explain the observed surface deformation.

Our results imply that these earthquakes occurred on a previously unknown normal fault rather than the southeastern branches of the nearby Muğla Fault as proposed earlier. The results are consistent with the recently mapped fault structure by Akyüz et al. (2018). The November activity implies EW trending, south dipping normal faulting system and the change in the strike direction of the fault on the eastern edge can be clearly seen both InSAR and waveform modelling results of April activity.

Co-seismic and post-seismic InSAR analysis shows that the seismic activity following the 2017 Mw6.6 Bodrum-Kos propagated from western Gökova Bay where rupture occurred toward east including the Ula region. A long term comparison of seismicity beneath Gökova Bay and Ula region shows that the seismicity in these two regions are temporally correlated. Hence, while the aforementioned moderate sized earthquakes are not directly triggered by the Bodrum-Kos earthquake, increased seismic activity following Bodrum-Kos earthquake shows that the stress changes in these two regions affect each other. The location errors of the events especially the depth errors in the catalogs and the active fault structure in the area cannot be realized without any geodetic or seismic data analysis. This study claims that the interpretations of the moderate size earthquakes should be studied by using multidisciplinary data sets.

ACKNOWLEDGEMENTS

This work is supported by the Turkish Directorate of Strategy and Budget under the TAM Project number DPT2007K120610.

How to cite: Eskikoy, F., Ergintav, S., Konca, A. Ö., Çakır, Z., Vasyura-Bathke, H., Isken, M., and Karabulut, H.: Small scale fault interactions in Southwestern Anatolia as revealed from Seismology & InSAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1068, https://doi.org/10.5194/egusphere-egu2020-1068, 2020.

Anatolia is part of the west-central Alpide plate-boundary zone, particularly where the deformation is characterized by the westward extrusion of this continental block between the Arabian-Eurasian collision in the east and the Hellenic Subduction in the west. Although, this motion mostly happens along the boundary structures, i.e., the North Anatolian and East Anatolian shear zones, there are multiple studies documenting the active deformation along NE-striking sinistral and NW-striking dextral strike-slip faults within the central and eastern parts of Anatolia. These secondary faults slice Anatolia into several pieces giving formation of the Malatya-Erzincan, Cappadocian and Central Anatolian slices from east to west, where their boundary geometries are strongly controlled by the weak zones, the Tethyan Suture Zones.

We compiled all geological slip-rate and palaeoseismological studies, which point out inhomogeneous magnitude of deformation along different sections of these secondary structures. The Central Anatolian Fault Zone, the westernmost NE-striking sinistral strike-slip structure and the western boundary between the Central Anatolia and Cappadocian slices, has an average horizontal slip-rate of about 1 to 1.5 mm/a for the last few tens of thousands of years. The earthquake recurrence of about 4500 years between two events revealed on the northern sections of the CAFZ also support this rate of deformation. However, the Malatya-Ovacık Fault Zone has a bimodal behaviour in terms of deformation rate, which is 2.5 times higher along its northern member, the Ovacık Fault (OF) than the southern one, the Malatya Fault (MF) (2.5 to 1 mm/a), respectively. This velocity difference between two distinct members of the same fault zone can be explained by the relative westward motion of slices where the OF makes the direct contact between the Central Anatolian and Malatya-Erzincan, and the MF delimits Cappadocian and Malatya-Erzincan slices. Although these structures, which are shallow and probably deform only the upper crust, are of having secondary importance, yet they are still capable of producing infrequent but strong earthquakes within this highly deforming convergent setting. This study is supported by TÜBİTAK projects no. 114Y227 and 114Y580.

How to cite: Zabcı, C., Sançar, T., Yazıcı, M., Friedrich, A. M., and Akçar, N.: Deformation of continental blocks within convergent plates: Anatolia as a case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18856, https://doi.org/10.5194/egusphere-egu2020-18856, 2020.

The present tectonic framework of the Western Anatolia has been dominated by two major deformations. The first one is the product of the slab-edge processes related to the convergence between Eurasian and African plates along with the Aegean-Cyprean subduction system since the Oligocene, and the second one is the westwards escape of Anatolian Block along the North Anatolian Fault Zone (NAFZ) since the late Miocene. The first one resulted in a widespread extensional deformation in the Western Anatolia and the Aegean region and is associated with slab-detachment and slab-tear processes that gave rise to the development of dynamic topography and various core-complexes (e.g., Cyclades and Menderes). Recent studies have shown that the deferential extensional strain between the core complexes in the region has been accommodated by strike-slip dominated transfer zones, the İzmir-Balıkesir Transfer Zone (İBTZ), which developed (sub)parallel to the extension direction and accommodate differential extension and rotational deformation in the region. The second one gave way to the development of a complex strike-slip deformation pattern and an array of pull-apart basin complexes throughout the northern margin of the Anatolian Block. The NAFZ and İBTZ interact around the Balıkesir-Bursa region resulting in a very peculiar deformation style due to partitioning of strain between these major structures.
This study aims at unraveling how the strain partitioning operates between İBTZ and NAFZ and to reveal the kinematic constraints that produced the present tectonic scheme in the region. The geometry and kinematics of the faults are determined by analyzing 2773 fault slip data obtained from 49 sites evenly distributed throughout the study area. The preliminary results show that the İzmir-Balıkesir Transfer Zone localized after Miocene with the decoupling of strike-slip faults, and to the episodic exhumation of the metamorphic core complexes. The focal mechanism solutions of the recent earthquakes support this decoupling and manifest the seismic activity of the İBTZ. This study is supported by a Tübitak Project, Grant Number of 117R011.

How to cite: Tosun, L., Çakır, E., Uzel, B., Sümer, Ö., Özacar, A. A., Kaymakcı, N., and Langereis, C.: Strain Partitioning Between the Izmir-Balikesir Transfer Zone and the North Anatolian Fault Zone, NW Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4116, https://doi.org/10.5194/egusphere-egu2020-4116, 2020.

In the complex tectonic setting of the Eastern Mediterranean, the westward motion of the Anatolian Block is accommodated mainly along its boundary faults, the North Anatolian Shear Zone (NASZ) and the East Anatolian Shear Zone (EASZ). Although there are relatively limited studies on the active tectonics of the EASZ, horizontal slip rate is suggested to be of about 10 mm/yr, using geodetic data. In terms of instrumental and historical seismicity, this sinistral strike-slip fault generated surface rupturing earthquakes along almost its entire length except two segments, Palu in the northeast and Turkoglu in the southwest, creating two seismic gaps on the East Anatolian Fault (EAF), the most prominent member of the EASZ. In spite of the fact that there are some off-fault seismic activities such as the 2010 Kovancılar Earthquake (M 6.1) in the vicinity of Palu Seismic Gap, recent geodetic measurements show significant aseismic creep, almost retaining the full far plate velocity (~10 mm/yr) for about 100 km-long section of the fault. Hence, the region is continuously monitored by various types of techniques, such as GNSS, InSAR, creepmeter, seismology, and high-resolution photogrammetry.

In addition to monitoring, we investigated the mechanical signature of the creep in the fault zone using fault rocks along the Palu Segment. We collected several samples directly from the deformation zone of the EAF, which makes the boundary between limestones of the Kirkgecit Formation and the chaotic alternation of volcanics, mudstones, and limestones of the Maden Complex, at two locations. The Underground Railway Tunnel Section (39.9504°N, 38.6976°E) is cut by the fault zone where the creep signals are recorded by a creepmeter. The X-Ray Diffraction (XRD) analyses of collected samples of this locality suggest the presence of montmorillonite (smectite group) as the main clay mineral in addition to chlorite-kaolinite with a negligible amount of illite-mica minerals within the fault rocks. This preliminary result suggests a linkage between the creeping and petrophysical properties of fault rocks, which are made of the weak smectite mineral and show no-frictional healing as the expected characteristics of the creep. However, the preliminary analyses of fault gouge samples from the Murat River Section (39.9696°N, 38.7043°E) yield a small amount of smectite group clays. We are going to extend our study at different locations in order to increase the spatial resolution on the relation between the fault rocks and creep motion. This study is supported by the TUBITAK Project no. 118Y435.

How to cite: Yazıcı, M., Basmenji, M., Köküm, M., Dogan, U., Zabcı, C., and Ergintav, S.: Contributions of fault gouge mineralogy on aseismic creep of active faults: the East Anatolian Fault (Eastern Turkey) as a case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-843, https://doi.org/10.5194/egusphere-egu2020-843, 2020.

The strike-slip dominated North Anatolian Fault Zone (NAFZ) prolongs to the west and furcates into several branches where shear is distributed to multiple parallel/subparallel segments. The earlier structures that resulted from the ongoing Western Anatolian extension had a key role in the fact that the western part of the NAFZ has a wider deformation zone. Although the southern boundary of this zone is controversial, it is proposed that there is a strong interaction between the deformation zones of the NAFZ and Western Anatolian Extensional Province (WAEP) along the northern margin of the Uludag Range. Since this pivotal region marks the transition between the extensional regime and continental strike-slip zone, it is necessary to increase knowledge thereof. Within this ongoing study, we focused on the morphotectonic and paleoseismologic properties of the Ulubat and Bursa faults that delimits the northern boundary of the Uludag Range. The results of the morphometric analyses (topographic symmetry factor, asymmetry factor, hypsometric curve and integral, channel concavity, and integral analyses) that performed on 79 drainage basin to the south of these faults suggested that the vertical motion in the northeastern part of the Uludag Range changes abruptly to strike-slip dominated deformation, along with Ulubat Fault, towards the west of the Bursa basin.

The 50 km length, dextral Ulubat Fault was mapped in the field by using offset physiographic features and geological evidence. We divided the ENE–WSW striking Ulubat Fault into three segments that present the releasing double-bend geometry. There are two major changes in trends up to 20 degrees between each segment. The western segment has a length of 17 km in the E-W direction. The middle segment extends toward NE with a length of 20 km. The eastern segment stretches eastward for 13 km with a southward arc-shape geometry. We conducted the first paleoseismological trench studies on middle and eastern segments of the Ulubat Fault and identified at least 6 paleoearthquakes for the last 16 ka on both segments. The paleoseismic behavioral results which are consistent with the geometric segmentation show individual ruptures on each segment. Dated surface ruptures history show that the fault has used the same single trace in Holocene and the last events occurred in 1143 AD and 170 AD along the middle and eastern segments respectively.

Although further studies are needed to evaluate the paleoseismic recurrence interval, our results show that the Ulubat Fault takes over a considerable activity in the north of Uludag Range. The field evidence and morphometric analyses around the Uludag Range sign out that the Ulubat Fault forms the southernmost member of the NAFZ strike-slip domain. The eastern segment of the dextral Ulubat Fault has vertical component while the Bursa Fault exhibits the characteristics of the WAEP towards further east. This research was supported by the Disaster & Emergency Management Authority of Turkey (UDAP project; G-18-01).

How to cite: Karabacak, V., Sançar, T., and Büyükdeniz, Y.: Paleoseismic and morphometric manifestation of the transition between the Western Anatolian extensional regime and the North Anatolian Fault strike-slip zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3161, https://doi.org/10.5194/egusphere-egu2020-3161, 2020.

Aseismic creep is detected and started to be monitored along the 100 km-long Palu-Hazar Segment of the Eastern Anatolian Fault (EAF) in Turkey, a major plate boundary between Anatolia and Arabia. We used creepmeters, InSAR, GPS, and seismic observations to document the extent and magnitude of this motion in order to increase our knowledge on the spatiotemporal variation of creep along the EAF, its relationship with the lithology and tectonic structures, and the stress change on the neighboring fault segments. Until now, we observed the region with continuous GPS and survey GPS measurements with near (~ 0.1- 4 km to the fault) and far-field (~25 – 225 km from the fault) stations to determine the depth of the creep zone and its velocity along the EAF. We processed 6 years (2014 – 2019) of continuous and 7 campaign (2015 – 2019) GPS data with GAMIT/GLOBK software. With elastic models, we determined a creep rate that reaches about 5 ± 0.3 mm/yr from GPS observations (50% of secular velocity). In addition to surface control of the creeping zone, we analyzed the deformations, by using three Terrestrial Laser Scanner (TLS) survey, in the Palu railway tunnel that crosses the fault where the walls of the tunnel have been offset by 15 ± 2 mm since the construction in the middle of the last century. Also, two creepmeters were installed inside the tunnel and transient creep anomalies are detected. These results are correlated with seismic and InSAR data (This study is supported by TUBITAK 1001 projects 114Y250 and 118Y450).

Keywords: Hazar-Palu, Creep, East Anatolian Fault, Earthquake, GPS, InSAR, TLS

How to cite: Dogan, U., Ergintav, S., Ozarpaci, S., Ozdemir, A., Erkoç, M. H., Yigitoglu, A., Ayruk, E. T., Çakir, Z., Karabulut, H., Bayram, B., Zabci, C., and Bilham, R.: Spatio-temporal variations of surface creep along the Hazar-Palu Segment of the East Anatolian Fault, Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11072, https://doi.org/10.5194/egusphere-egu2020-11072, 2020.

The Dead Sea Transform fault forms the boundary between the Arabian plate and the Sinai-Levant subplate. Several aspects of this fault system have been extensively studied during the last century. However, the present-day kinematics and deformation along its southern end in the Gulf of Aqaba remain poorly understood. Here we present a crustal motion velocity field based on three GPS surveys conducted between 2015 and 2019 at 30 campaign sites, complemented by 12 permanent stations operating near the gulf. We constrained a pole of rotation for the Sinai-Levant subplate based on five selected stations on the Sinai Peninsula. This Euler pole predicts a left-lateral slip rate of ~4.5 mm/yr on the fault system in the gulf, consistent with earlier findings. We find that standard models of interseismic deformation, such as back-slip and screw dislocation models do not provide a reasonable constraint on fault locking depths due to limited near-fault measurements. Despite this, our results reveal a small (~1 mm/yr) but systematic left-lateral residual motion across the gulf that cannot be resolved by elastic models of strain accumulation. We further find that the orientation of these residuals agrees with modelled postseismic transient motions caused by the 1995 M_W 7.2 Nuweiba earthquake in the NE and SW quadrants relative to the gulf trend. Combined, these observations suggest that postseismic deformation caused by the Nuweiba earthquake may still be ongoing. We anticipate our findings to be a starting point for future geodetic studies in the northern Red Sea region where large-scale infrastructure mega-projects, such as the NEOM city and the King Salman bridge across the gulf are being developed. Future studies would benefit from incorporating additional GPS stations on the Sinai side of the gulf, refined finite-fault models, seafloor geodetic measurements and better information about past earthquakes.

How to cite: Castro-Perdomo, N., Viltres, R., Masson, F., Ulrich, P., Bernard, J.-D., Dhahry, M., Liu, S., Alothman, A., Zahran, H., Mai, P. M., and Jónsson, S.: Interseismic Deformation in the Gulf of Aqaba Inferred from GPS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13045, https://doi.org/10.5194/egusphere-egu2020-13045, 2020.

On 7 November 2019 (22:47 UTC) a M_w 5.9 earthquake struck the East-Azerbaijan region, in the north-western Iran, about 100 km east of Tabriz, the fourth largest city of Iran with a population of over two million. This seismic event caused both widespread damage to the surrounding villages and casualties, killing about 5 people and injuring hundreds. The occurrence of this earthquake is related to the main geodynamic regime controlled by the oblique Arabia-Eurasia convergence and, in particular, this event is inserted in the tectonic context of the East-Azerbaijan Plateau, a complex mountain belt that contains internal major fold-and-thrust belts.

In this work, we first generate the coseismic deformation maps by applying the Differential Synthetic Aperture Radar Interferometry (DInSAR) technique to SAR data collected along ascending and descending orbits by the Sentinel-1 constellation of the European Copernicus Programme. Then, we invert them through analytical modeling in order to better constrain the geometry and characteristics of the main source. The retrieved fault model revealed a shallow seismic source approximately NE–SW-striking and characterized by a left-lateral strike-slip, southeast-dipping faulting mechanism. Our retrieved solution reveals a new minor fault never mapped in geological maps before, whose kinematics is compatible with that of the surrounding structures and with the local and regional stress states. Moreover, we also use the preferred fault model to calculate the Coulomb Failure Function at the nearby receiver faults; taking into account the surrounding geological structures reported in literature, we show that all the considered receiver faults have been positively stressed by the main event. This is also confirmed by the distribution of the aftershocks that occurred near the considered faults. The analysis of the earthquake nucleated along these left-lateral strike-slip minor fault is essential to improve our knowledge of the East-Azerbaijan Plateau; therefore, further studies are required to evaluate their role in seismic hazard definition of northwest of Iran, in order to help in the mitigation of the seismic hazard in seismogenic regions unprepared for the occurrence of seismic events.

This work is supported by: the 2019-2021 IREA-CNR and Italian Civil Protection Department agreement, H2020 EPOS-SP (GA 871121), ENVRI-FAIR (GA 824068) projects, and the I-AMICA (PONa3_00363) project.

How to cite: Valerio, E., Casu, F., Convertito, V., De Luca, C., De Novellis, V., Manunta, M., Manzo, M., Monterroso, F., and Lanari, R.: Seismogenic source model of the 2019 Mw 5.9 East-Azerbaijan earthquake (NW Iran) through Sentinel-1 DInSAR measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20404, https://doi.org/10.5194/egusphere-egu2020-20404, 2020.