TS4.1

        The Cenozoic geodynamic evolution of the Western Mediterranean is complex comprising subduction, slab roll-back, back-arc extension, collision, and lithosphere delamination. We investigate the subsidence of a regionally observed unconformity in the Valencia Trough of the Western Mediterranean, here referred to as the Miocene Unconformity, which separates Mesozoic from latest Palaeogene to Neogene sediments. The mechanisms controlling its subsidence are poorly understood.

        We show, using a dense grid of seismic reflection data, well data and 3D flexural backstripping, that the Miocene Unconformity in the SW Valencia Trough subsided by more than 1.5 km to the present day at an average rate of 90 m/Myr. The absence of Cenozoic extensional faults affecting the basement shown by seismic data indicates that this rapid subsidence is not caused by Cenozoic rifting or remaining Mesozoic post-rift thermal subsidence. Neither can this subsidence be explained by subduction dynamic subsidence or flexural loading related to the thin-skin Betic fold and thrust belt which only affects subsidence observed near the deformation front.

        We interpret the 1.5 km subsidence of the Miocene Unconformity as the collapse of a back-arc transient uplift event. Erosion during this uplift, resulting in the formation of the Miocene Unconformity, is estimated to exceed 4 km. Transient uplift was likely caused by heating of back-arc lithosphere and asthenosphere, combined with mantle dynamic uplift, both caused by segmentation of Tethyan subduction resulting in slab tear. Subsidence resulted from thermal equilibration and the removal of mantle flow dynamic support Tethyan subduction slab roll-back. We propose that our observations and interpretation of rapid back-arc km-scale uplift and collapse have global applicability for other back-arc regions experiencing subduction segmentation and slab tear during subduction slab roll-back.

How to cite: Fang, P., Tugend, J., Mohn, G., Kusznir, N., and Ding, W.: Rapid large-amplitude vertical motions generated by 3D subduction slab roll-back in the Valencia Trough, Western Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2092, https://doi.org/10.5194/egusphere-egu22-2092, 2022.

SE Iberia Tectonics is presently dominated by the NNW-SSE convergence between the Eurasian and Nubian plates. Farther east, the eastern Spanish coast and the Valencia Trough are dominated by ENE-WSW extension related to thermal subsidence. This extension has been interpreted as the final stage of abort rift responsible for the ENE motion of the Balearic promontory. Our data from 11 CGNSS stations permit us to discuss the deformation partitioning in SE Iberia related to the two abovementioned processes.

We identify three kinematic domains: a relatively stable domain, a domain moving towards NNW and undergoing NNW-SSE shortening, and a third domain relatively moving towards ENE and experiencing ENE-WSW extension. Our results indicate that plate convergence-related NNW-SSE shortening is mainly absorbed by the Eastern Betic Shear Zone (EBSZ), in agreement with previous studies, but also show that a significant fraction of this shortening is accommodated south of the EBSZ.

We also identify and quantify for the first time ENE-WSW extension northeast of the EBSZ. We propose that this extension could be absorbed by basement normal faults whose surface expression is obscured due to decoupling of deformation between the basement and the cover. Our results shed light on the tectonic puzzle of SE Spain.

How to cite: Martin-Rojas, I., Sánchez-Alzola, A., Medina-Cascales, I., Borque, M. J., Alfaro, P., and Gil, A.: Present strain partitioning in SE Spain. Insights from CGNSS data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5227, https://doi.org/10.5194/egusphere-egu22-5227, 2022.

We here discuss the results of a local GNSS episodic network from the Baza sub-Basin (S Spain). This network including six sites, was established in 2008 and has been measured seven times since then. Our data permit us to present the first short-term slip rates for the two active faults in this area. The main active structure is the normal Baza Fault. We estimate slip rates for this fault ranging between 0.3±0.3 mm/yr and 1.3±0.4 mm/yr. For the strike-slip Galera Fault, we quantify the slip rate as 0.5±0.3 mm/yr. These values are higher than previously reported long-term slip rates. We postulate that the discrepancy for the Baza Fault between short-term and long-term slip rates could indicate that the fault is presently in a period with a displacement rate higher than the mean of the magnitude 6 seismic cycle. Moreover, the velocity vectors that we obtained also show the regional tectonic significance of the Baza Fault, as this structure accommodates one-third of the regional extension of the Central Betic Cordillera.

Our results also show that the Baza and Galera Faults are kinematically coherent and they divide the Baza sub-Basin into two tectonic blocks. This points to a likely physical link between the Baza and Galera Faults; hence, a potential complex rupture involving both faults should be considered in future seismic hazard assessment studies.

How to cite: García-Tortosa, F., Alfaro, P., Sánchez-Alzola, A., Martin-Rojas, I., Galindo-Zaldívar, J., Avilés, M., López Garrido, A. C., Sanz de Galdeano, C., Ruano, P., Martínez-Moreno, F. J., Pedrera, A., de Lacy, M. C., Borque, M. J., Medina-Cascales, I., and Gil, A. J.: Kinematic and tectonic analysis of the Baza and Galera Fault (S Spain). Insights from GNSS data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5479, https://doi.org/10.5194/egusphere-egu22-5479, 2022.

The Algero-Balearic Basin (ABB) is an Oligo-Miocene back-arc basin resulting from a polyphase tectonic evolution involving Tethyan subduction retreat and bilateral slab tear propagation. The ABB was fully opened by the Tortonian, while the Gibraltar and Calabria arcs formed by the narrowing of retreating slab fragments. Since then, the Algerian margin has undergone a tectonic inversion, potentially preceding an incipient subduction as shown by the analysis of the on-offshore deformation distribution. In this work, we aim to shed light on the relationships between the large-scale structures inherited from the ABB opening and the recent margin inversion. For this purpose, we rely on two recent analyses, one addressing the ABB opening (Haidar et al., 2021) and the other mapping the inversion-related structures off-Algeria (Leffondré et al., 2021), both being constrained by a set of deep penetration multi-resolution seismic profiles cross-correlated with magnetic, gravimetric and bathymetric data. 

The deep ABB has been subdivided into 4 zones with relatively distinct geodynamic evolutions, as demonstrated by variations in pre-Messinian sedimentary infill thickness and basement depth : (1) the oldest, fan-shaped oceanic basin to the east (off-Jijel), formed during the Langhian-Serravallian after collision of the Kabylian blocks with the stretched African margin; (2) the shallower and younger Hannibal thinned continental domain (HD), intruded by intense post-collisional magmatic activity during the Upper Serravallian - Lower Tortonian; and ever-younger to the west, (3) the central-western (off-Algiers-Tipaza) and (4) westernmost zones, formed from the Tortonian to the Lower Messinian in response to the westward retreat of the Gibraltar slab and the concomitant migration of the Alboran block by propagation of vertical tears along a STEP (Subduction Transform Edge Propagator) type margins.

The tectonic inversion is characterised by long-wavelength of flexure (>100km) of the ABB towards the Algerian margin and/or buckling of shorter wavelengths (≈30km). The central (HD) and central-eastern (off-Jijel) zones are dominated by flexure, whereas buckling is dominant in the central-western zone. Further, the easternmost (off-Annaba) and westernmost zones exhibit a combination of flexure and buckling. Except in the westernmost zone, characterized by low deformation on a single fault, the margin toe consistently displays inversion-related faults systems consisting of 3 to 4 south-dipping and sub-parallel thrust faults.

By comparing the zonation of the deep ABB and the zones with different responses to inversion, we evidence a similar zonation of the margin, with only slight differences likely resulting from data density variations. To the east, the old and wide fan-shaped basin has favored the development of a significant flexural response, whereas the young westernmost zones, narrower and bordered by STEP-faults, evidence a combination of buckling and short-wavelength of flexure. The HD is a complex zone with a shorter wavelength of flexure compared to the eastern zone, probably related to magmatic activities affecting the potentially continental crust. Our results suggest that if initial zonation persists, several parameters may be involved in the control of the inversion mode. These parameters may include the opening-related structural inheritance, the oceanic lithosphere composition, as well as the age and former structures of the margin.

How to cite: Haidar, S., Leffondré, P., Déverchère, J., Graindorge, D., Klingelhoefer, F., Arab, M., Medaouri, M., and Beslier, M.-O.: New insights on the relationship between inherited structures of the opening of the Algero-Balearic basin and recent inversion of its southern margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12611, https://doi.org/10.5194/egusphere-egu22-12611, 2022.

This work analyses the tectonic evolution of Northern Tunisia from the Late Miocene to Present. Two orthogonal extensional systems with ENE- and SE-directed transport produced the extensional collapse of the Tell and Atlas Foreland Thrust Belts (FTBs) in northern Tunisia during the Late Miocene to Pliocene in a context of NW-SE plate convergence between Africa and Eurasia. These systems produced the extensional denudation of the Tunisian Atlas and Tell foreland thrust belts, which we related to deep mantle tectonic mechanisms, known as a common feature in other FTB´s in the western Mediterranean, i.e. Betics, Rif, Calabria and Apennines. Low-angle normal faults have extended and reworked the Tunisian Tell external foreland thrust belt, exhuming midcrustal lower-greenschist metapelites and marbles with Triassic protholiths, and forming Late Miocene basins. This extension was followed by later Pliocene to Present tectonic inversion, developing the active shortening structures in Northern Tunisia. The main shortening structure is formed by different reverse and strike-slip fault segments, linked forming the 130 km long Alia-Thibar fault zone. Restored Plio-Quaternary deformation observed on reflection seismic lines indicates deformation rates around 0.6-0.8 mm/yr in the studied segments and larger amounts of shortening to the West of Northern Tunisia (16%) than to the East (7%), which suggests that tectonic inversion started earlier to the West and later propagated eastwards, reaching Northeastern Tunisia in the Late Pliocene. Due to the young age of this tectonic inversion, the present relief of Northern Tunisia is characteristic of a young thrust and fold belt, with dominating axial valleys along synforms and an incipient transverse drainage development propagating from West to East.

How to cite: Gaidi, S., Melki, F., Booth-Rea, G., Marzougui, W., Pérez-Peña, J. V., Ruano, P., Galve, J. P., Chouaieb, H., Azañón, J. M., and Zargouni, F.: Neogene to recent geodynamic evolution of Northern Tunisia foreland thrust belt., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10619, https://doi.org/10.5194/egusphere-egu22-10619, 2022.

The Apennine Tyrrhenian margin records the evolutionary steps of the back-arc basin developed at the rear of a E-ward migrating fold-and-thrust belt. As well-documented in literature, the counterclockwise rotation of the Apennines is related to the southward increase of the roll back-related subduction of the Adria slab. This led first to the progressive incorporation of thrust sheets within the Apennine prism in the upper plate and later to its subsequent back-arc extension that is contemporaneous with the continuate inarching of the Apennine front towards the Adriatic and Ionian seas. Uncertainties arise on the structural style and timing in the internal Apennines between the orogenic and post-orogenic stages, that are respectively represented by thrust-sheet implacement, and crustal thinning.

We hereby propose a combined 2D seismic and field data review that allows identifying the geodynamic processes preceding the crustal stretching of the Apennine Tyrrhenian margin with new insights from on- and off-shore seismic lines. In particular, the construction of a new geotraverse across the margin, which is stretched over 100 km between the internal Central Apennines belts and the Pontian escarpment, allows to roughly estimate: i) the Late Miocene - Earliest Pliocene shortening with its change of the basal decollement depth through time; in particular, subsurface data highlighted stacked thrust sheets that were involved in an initial in-sequence propagation with top-to-the-ENE, synchronous to late Tortonian foredeep to wedge-top sedimentation. We also distinguish late backthrusts related to the formation of triangle zones that are more deeply rooted moving to the western chain interior. ii) The amount of crustal stretching and subsidence; Back arc-related orogenic collapse is preceded by initial orogen uplift and erosion in the internal sectors. iii) The onset of at least two magmatic cycles; in this frame, the lateral slab tearing and retreat is tracked by E-rejuvenated volcanic activity in the upper plate along the Volsci Volcanic Field and the Palmarola-Vesuvius lineaments. Those volcano-tectonic trends are favoured by a series of transtensive structures that progressively reflect the arc expansion in the rear. In this frame, the NE-dipping crustal detachment(s) may have played into crustal thinning during the Pliocene, driving and occasionally hampering magma emplacement, while high-angle faults have locally driven monogenetic eruptions. Finally, we report on field and seismic evidence of neo-tectonics, supporting ongoing extension occurring on the margin.

How to cite: Vico, G. and Cardello, G. L.: From thrusting to back-arc extension: seismic structure and field evidence of the Apennine Tyrrhenian margin (Central Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9955, https://doi.org/10.5194/egusphere-egu22-9955, 2022.

How to cite: Broerse, T., Govers, R., and Willingshofer, E.: Delayed lithosphere tearing along STEP Faults, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5335, https://doi.org/10.5194/egusphere-egu22-5335, 2022.

The eastern Mediterranean is shaped by the interaction between the African, Arabian, and Eurasian plates resulting in a complex tectonic framework. The Hellenic subduction is well documented and studied but, the northeast corner of the eastern Mediterranean Sea remains enigmatic. It is a tectonically active region where different plate boundary conditions coexist (i.e., oceanic subduction, continental collision, extension, and strike-slip movements). An active and tsunamigenic system has been interpreted west and east of Cyprus by using deep seismic reflection lines. Vintage deep-penetrating seismic reflection profiles of the Mediterranean Sea project (MS project) - acquired during the ’70 - were re-analyzed and merged with a synthesis of available subsurface data from the scientific literature. This study focuses on two transects (MS53 and MS56) that cross the major offshore structures (i.e., Florence Rise, Latakia Ridge, and Kyrenia Ridge) from north to south. The western transect (MS53) shows the Herodotus oceanic crust subducting northward beneath the Eurasian plate. The Florence Rise is the leading edge of the system, and the Antalya Basin is its forearc basin. Close to the Turkish coast, a buried block seems to act as a backstop for the offshore system, and north of it, some out-of-sequence thrusts have been interpreted. The strain is partitioned between the Florence Rise and the Taurides front. The eastern transect (MS56) crosses the Latakia Ridge, i.e., the northern boundary of the Levant Basin, where shortening is greater than in the western area. The seismic line continues northward into the Cyprus – Latakia Basin, crossing the Kyrenia Ridge, and reaching the Turkish coast. On the seismic section, we interpreted the Mesozoic subduction front now hindered by strike-slip movements on the Latakia Ridge. Another prominent transpressive structure is the Kyrenia Ridge, which is interpreted as an active structure with a well-imaged thrust system in front of it. The seismic sections were depth converted to provide a regional geologic model for the northeastern Mediterranean Sea. Active subduction fronts, which are only partially imaged, were structurally modeled and then crosschecked with previous studies to better constrain their geometry. In the northeastern Mediterranean Sea, a plate boundary is buried offshore with active subduction west of Cyprus and mainly transpressional tectonics to the east. A better understanding of its nature and kinematics would be useful to assess the tsunami hazard in this area.

How to cite: Bertone, N., Bonini, L., Colin, E., Del Ben, A., Brancatelli, G., Camerlenghi, A., Forlin, E., and Pini, G. A.: Subduction hints from the northeastern Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8675, https://doi.org/10.5194/egusphere-egu22-8675, 2022.

Many of the most hazardous volcanoes lie in rift systems, where tectonics often seems to exert control on magma emplacement. However, our current knowledge of the interplay between volcanism and tectonics is immature due to the lack of observations on geological time scales. Located in the southern Aegean Sea, the Christiana-Santorini-Kolumbo (CSK) volcanic field lies in a prominent continental rift zone caused by back-arc extension along the Hellenic Arc. Covered by numerous geophysical surveys, this area offers the unique possibility to reconstruct a volcanic rift in time and space. Previous studies have revealed that the CSK volcanic field developed during four distinct volcanic phases, which initiated in the Pliocene and only recently matured to form the vast Santorini edifice. Here, we combine P-wave velocity tomography models and high-resolution reflection seismic data to reveal the internal architecture and the spatio-temporal evolution of the rift basins as well as their relation to the evolution of the CSK volcanoes. Our joint analysis reveals a distinct NE-SW-directed horst-structure separating the volcanic rift into a volcanically active northwestern zone and a volcanically inactive southeastern zone. Using a refined seismo-stratigraphic framework of the internal architecture of the rift basins, we identify four distinct phases of the rift system that correspond to the volcanic phases of the CSK field. These phases reflect the gradual development of a Pliocene-Pleistocene NE-SW oriented fault system overprinting an older Miocene-Pliocene ESE-WNW oriented fault system. The latest volcanic phase, during which volcanism focussed on Santorini and became highly explosive, corresponds to a distinct shift in the tectonic behavior of the rift system after which enhanced subsidence at the Santorini-Anafi and Amorgos faults occurred that was rapidly filled up by thick volcano-sedimentary deposits. We conclude that the volcanism of the CSK field is fundamentally controlled by NE-SW-directed rifting, which lies parallel to the Pliny and Strabo trends of the southeastern Hellenic Arc. This volcanic system is bounded to the southeast by the Akrotiri-Anhydros horst, which seems to be a deep-rooted structural boundary for the volcanic plumbing system. The shift from ESE-WNW directed faulting to NE-SW directed faulting is an indication that the dominant direction of slab-rollback driving the extension of the CSK rift shifted from the southwestern to the southeastern Hellenic Arc with Santorini lying at the hinge of these trends.

How to cite: Preine, J., Hübscher, C., Karstens, J., Hooft, E., and Nomikou, P.: This Rift is on Fire: Volcano-Tectonic Evolution of the Christiana-Santorini-Kolumbo volcanic field, Aegean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2986, https://doi.org/10.5194/egusphere-egu22-2986, 2022.

Although damaged speleothems have been widely investigated to study paleo-earthquake records in caves, only few reports could directly link damages to specific recent earthquakes. We mapped before the 2017 M_w 6.6 Bodrum–Kos earthquake the so-far unexplored Korakia Cave on Pserimos island in the Dodecanese (Greece), which is located at the transition between the Aegean and Anatolian region and is known for its strong seismicity. The cave formed along an active normal fault and records numerous broken columns and flowstones sealed by younger speleothems. New ²³⁰Th/U-ages show that paleoseismic events occurred since the formation of the cave, which is older than the limit of the dating method. During a cave visit 2 months after the 2017 M_w 6.6 Bodrum–Kos earthquake we noted that c. 10 cm small stalactites, which were actively growing along fractures in the cave ceiling, have been chipped off by movements along the fractures and were lying on flowstones covered by greenish biofilms. Removal of the broken fragments demonstrated that the chlorophyll pigment below the position of the fragments did not show a colour difference to the surrounding area, which is exposed to the daylight of the cave entrance. The preservation of the photoautotrophic biofilm, which can survive only a few months without daylight, suggests that the stalactites have been broken by the 2017 M_w 6.6 Bodrum–Kos earthquake, which also caused the collapse of several buildings on the island of Kos only 4 km S of Pserimos. We conclude that earthquake capable of causing small shear displacements on fractures can damage speleothems. However, other delicate speleothems including long and slim stalactites remained undamaged.

How to cite: Grasemann, B., Plan, L., Baron, I., and Scholz, D.: Speleothem deformation due to the 2017 Mw 6.6 Bodrum–Kos earthquake in a cave on Pserimos (Dodecanese, Greece), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-164, https://doi.org/10.5194/egusphere-egu22-164, 2022.

Continental transform faults are generally known to have widely distributed structures and sparse seismicity, in opposite to their oceanic counterparts. The North Anatolian Shear Zone (NASZ) is an ideal example, where the total deformation is shared between multiple structures especially during its evolutionary stages. The North Anatolian Fault (NAF), the most prominent member of the NASZ, started to form of about 11 Ma in the east and propagated to the west, reaching to the Marmara Sea only a few hundred thousand years ago. This principal displacement zone generally extends as a single strand from its easternmost tip to the west until Bolu for about 900 km. To the west of Bolu, it bifurcates into two branches, Düzce and Mudurnu Valley segments, delimiting the Almacık Flake (AF) respectively to the north and south. Although there is a considerable number of multi-disciplinary studies on the kinematics and history of active faulting within and around the AF, we still have gaps in our knowledge on (a) the ratio of strain distribution, (b) time of formation of bounding fault segments and (c) their evolutionary stages.

In order to fulfil some parts of this gap, we studied the major morphometric indices, including hypsometric curve and integral (HI), asymmetry factor (Af), channel concavity (θ), chi (χ) and knickpoint analyses on drainage basins across the whole AF and all surrounding fault segments. Our goal is not only to document the comparative tectonic effect of the bounding fault segments on the topography, but also to test any potential cumulative morphological response to pre- and post-peak structures, especially along the Düzce Segment. Almost all of 83 extracted drainage basins yield high HI values, usually ranging between 0.4 and 0.72, and suggest a rejuvenating morphology compatible with the general ‘uplift hypothesis’ for the AF. In more details, θ and χ values point out the strong and confined effect of the active bounding faults. Moreover, knickpoints do not show evidence for any pre-peak structures rather than recent active faulting. This may be result of limited size, thus ages, of drainage basins, which are cut by bounding faults at both sides of the AF. Alternatively, these fault segments may be older than previous assumptions, whereas the effect of pre- and post-peak shear structures on topography has already been erased mainly by external processes. On the other hand, χ values, based on 0.45 reference θ, suggest a high incision along the western sections of the Mudurnu Valley Segment, which may indicate a strain transfer from north to south. Nevertheless, the breach of a landslide dam of about 5750 years ago and the strong incision of the Mudurnu River following this event to the south of the AF, as suggested by previous studies, can be another reason for this anomaly. Briefly, our preliminary results suggest a strong tectonic control on the AF’s topography mainly due to the activity of the bounding structures. We do not see any morphometric evidence for the secondary (pre- and post-peak) faults in the near past of the NASZ around the AF.

How to cite: Kiray, H. N., Sançar, T., and Zabcı, C.: Spatial strain distribution along continental transform faults: insights from morphometric analyses of the Düzce and Mudurnu Valley segments (North Anatolian Fault, NW Turkey), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-459, https://doi.org/10.5194/egusphere-egu22-459, 2022.

The occurrence of earthquake-repeaters, i.e. co-located seismic events of comparable magnitude with highly similar waveforms breaking the same fault patch with an almost identical mechanism, is generally regarded as an indication that the fault surrounding the earthquake asperity is (aseismically) creeping. Earthquake repeaters can either occur during transient loading, e.g. within the afterslip of large earthquakes, or during the constant tectonic loading of tectonic faults. In this study we consider the latter.

The Main Marmara Fault (MMF) belongs to the western part of the North Anatolian Fault Zone (NAFZ) between the Anatolian and Eurasian plates and runs close to the population centre of Istanbul below the Marmara Sea. While the main NAFZ branches to the east and west of the MMF ruptured in M>7 earthquakes in the last century, the MMF itself is regarded as a seismic gap with the potential to host an M>7 event in the near future. Knowledge about the amount of aseismic creep of the off-shore MMF strand is important for a better seismic hazard assessment for the city of Istanbul and is heavily debated.

Building on earlier studies that identified repeating earthquakes in the western part of the MMF, we investigate a newly compiled seismicity catalogue of the Sea of Marmara for repeating events along the complete MMF. The catalogue spans the time period 2006-2020, comprises almost 14,000 events in the magnitude range M0.3-M5.7 and was compiled from regional permanent stations operated by AFAD and KOERI. Phase onset times were automatically picked with a two-step procedure using higher-order statistics and an AIC-representation of the waveforms for crude and fine-tuned estimation of the P- and S-onsets. The resulting onset-times were used in the Oct-tree location algorithm of the probabilistic NLLoc software using a regional velocity model and station corrections to obtain the final hypocentres.

To search for earthquake repeaters, we divide the MMF into overlapping segments and perform a station-wise cross-correlation analysis for all available event waveforms in each segment. Correlated waveforms start 1 s before the P-wave arrival and include the complete waveform including the S-wave coda. Waveforms were bandpass filtered between 2 and 20Hz to retain a rather wide frequency spectrum. We apply strict selection criteria and identify repeating events only as those with a normalized cross-correlation coefficient larger than 0.9 at at least 3 stations and a temporal separation of more than 30 days to exclude bursts of highly similar events in aftershock sequences or earthquake swarms.

The highest density of repeating earthquakes is found below the western Marmara Sea (Central Basin and Western High) with a systematic decrease of repeaters towards the east (Kumburgaz Basin) and none at all in the presumably locked Princess Islands section of the MMF immediately south of Istanbul. These results for the first time provide a consistent image of the amount of creep along the entire overdue Marmara section of the NAFZ derived from permanent onshore stations refining earlier results obtained from individual spots using local seafloor deployments.

How to cite: Becker, D., Martínez-Garzón, P., Wollin, C., and Bohnhoff, M.: Systematic variations of fault creep along the Marmara seismic gap, north-western Turkey, based on the observation of earthquake repeaters obtained from a high-resolution regional earthquake catalogue, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8142, https://doi.org/10.5194/egusphere-egu22-8142, 2022.

Recent observations suggest that seismogenic faults release elastic energy not only during sudden earthquakes but also aseismically. Slow slip can be persistent, lasting for years, or episodic. Aseismic slip is thought to be influenced by the presence/migration of fluids, stress interactions through fault geometrical complexities, or fault material heterogeneities. However, slow slip events have mostly been captured by regional GNSS networks in subduction zones, and the finest details of the nucleation, propagation, and arrest of such events have not been observed yet. Therefore, continental creeping faults are ideal targets for tackling such observational gaps and focusing on the sub-daily behavior of such slow slip events.

The central segment of the North Anatolian Fault is known to be creeping at least since the 1950s. This region was struck by the Mw 7.3 Bolu/Gerede earthquake in 1944, and since then, no earthquake of magnitude greater than 6 has been recorded. During the 1960s, aseismic slip was discovered as a wall built across the fault in 1957 was being slowly offset. Geodetic studies (InSAR, GNSS, and creepmeters) focused on capturing and analyzing aseismic slip around the village of Ismetpasa. Creepmeter measurements during the 1980s and 2010s, along with InSAR time series analysis, suggest that aseismic slip occurs episodically rather than persistently. However, no permanent GNSS stations were available close enough to the fault to study the details of such slow slip events.

Within the scope of a French-Turkish collaboration, we installed 17 GNSS stations (ISMENET) in 2019 to survey the spatio-temporal evolution of aseismic slip rate and characterize the physical properties of the fault zone. A creepmeter array located in the Ismetpasa village reported the occurrence of a significant slow slip event between December 2019 - January 2020. We analyze the GNSS record to search for small aseismic slip episodes and describe their behavior. We use a combination of Multivariate Singular Spectrum Analysis (MSSA) and Geodetic Template Matching (GTM) to extract the signature of aseismic slip and characterize its source. Results are compared to creepmeter measurements, as well as the historical earthquakes, fault geometrical complexities, and kinematic coupling. Our results confirm that aseismic slip in the region is not permanent. Therefore, even though the aseismic slip rate in the long-term seems to be constant, such a rate might result from the contribution of many aseismic slip episodes as the one detected in this work.

How to cite: Jara, J., Ozdemir, A., Dogan, U., Jolivet, R., Çakir, Z., and Ergintav, S.: Slow slip events captured by GNSS  along the Central Section of the North Anatolian Fault, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9541, https://doi.org/10.5194/egusphere-egu22-9541, 2022.

Crustal deformation and seismic activity in the Levant is mainly related to the interplate Dead Sea Fault (DSF) and the intraplate Carmel-Gilboa Fault System (CGFS). In this study we analyze the interseismic deformation along these fault systems using 23 years of GPS measurements obtained from 209 campaign and 60 continuous stations. This GPS dataset is the longest record and the densest dataset for the DSF and the Levant region. We use this dataset to investigate the spatial variations of slip and creep rates along the southern and central sections of the DSF and the CGFS. Our inversion model results indicate that part of the tectonic motion is transferred from the DSF to the CGFS. We find that the left-lateral strike-slip motion along the DSF decreases in a rate of 0.9±0.4 mm/yr, from 4.8±0.3 mm/yr south to the intersection with the CGFS, to 3.9±0.4 mm/yr north to this intersection. Along the CGFS the left-lateral strike-slip motion ranges between ~0.3-0.5 mm/yr and the extension rate between ~0.6-0.7 mm/yr, indicating a total slip rate vector of 0.8±0.4 mm/yr in the DSF direction, in agreement with the reduction of slip rate along the DSF near the intersection with the CGFS. Shallow creep is found along the southern and central sections of the Dead Sea basin and the northern Jordan Valley section of the DSF, with creep rates of 3.4±0.4 and 2.3±0.4 mm/yr, respectively. These creeping sections were identified as areas with thick salt layers at the shallow subsurface. We suggest that shallow creep behavior along the DSF is govern by the presence and mechanical properties of the salt layers, which probably allows plastic deformation and the transition to velocity strengthening at the shallow subsurface and promotes creep.

How to cite: Hamiel, Y. and Piatibratova, O.: Spatial variations of slip and creep rates along the Dead Sea Fault and the Carmel-Gilboa Fault System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3591, https://doi.org/10.5194/egusphere-egu22-3591, 2022.

The tectonic nature of the Sinai Microplate's western boundary is clouded with uncertainties. Early studies suggested that the western edge of Sinai is fully connected to the African Plate, thus concluding that Sinai is a sub-plate. Later, bathymetric analyses of prominent lineated faults straddling across the western edge of the Levant Basin have suggested that, in fact, this area is a plate boundary that accommodates dextral motion between the African Plate and the Sinai Microplate. However, this inference contradicts geological and geophysical observations across the Gulf of Suez, the southern continuation of the same plate boundary. Here we present preliminary results from a recent geophysical cruise aboard the R/V Bat Galim. We focused our investigation on one of the major faults, oriented in an NW-SE direction (located ~80 km southwest of the Eratosthenes Seamount), creating the plate boundary. We collected high-resolution shallow multichannel seismic reflection data complemented with multibeam bathymetry data. We also acquired two piston cores near the trace of the fault. These observations unravel the shallow three-dimensional structure of the fault system whereby several curved and steeply dipping normal fault segments are splayed from the main fault trace in a westerly direction. These secondary faults display a back-tilted and step-like morphology. This structure is best explained by a sinistral motion acting along the master fault. Independently, we present an updated Africa-Sinai Euler pole based on the motion of GPS stations recorded between 1996 and 2019. The results suggest that Sinai is moving in a northwesterly direction with respect to Africa (1.7-1.9±0.9 mm/yr). Focal mechanism solutions calculated for recent earthquakes occurring in this region (Mw>4.5) agree with the geodetic constraints of a sinistral relative motion.

Overall, these observations suggest that the western boundary of Sinai has been, and still is, accommodated sinistral motion relative to Africa. This conclusion implies that the Sinai Microplate is moving faster with respect to Eurasia relative to the motion of Africa with respect to Eurasia. This, in turn, seems to be in conflict with the notion that subduction of the oceanic lithosphere north of the Sinai Microplate (i.e., east of Cyprus) has recently ceased. We speculate that the downgoing slab might still promote the relatively fast northward motion of Sinai and/or a northward drag force induced by large-scale mantle flow related to the Afar plume could also contribute to the motion of the Sinai Microplate.

How to cite: Granot, R., Katz, O., Kanari, M., Hyams, O., and Hamiel, Y.: New constraints on the kinematics of the western Sinai Microplate: geodynamic implications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9537, https://doi.org/10.5194/egusphere-egu22-9537, 2022.

We propose that lithospheric collision of Africa and Eurasia is incipient throughout the entire East Mediterranean. Our evidence confirms the incipient continent-continent collision that has been recently proposed for the Cyprus Arc and showcases how collision is expressed at depth and across the Hellenic Arc. We provide evidence of basin-wide lithospheric-scale collision by coupling, at tectonic scale (1.5M km²), quantitative joint analysis of submarine and terrestrial relief, and the interpretation of a compilation of regional vintage multichannel seismic data (>46.000 km), reprocessed with modern techniques. No megathrust surface marking a subduction interplate contact is imaged in any seismic line, and the relief across sedimentary piles is not shaped as mechanically-accreted wedges. Instead, continent-continent collision is expressed across plates in two modes along longitude. In the offshore regions south of Cyprus and Crete, submarine thrust systems with no frontal structure nor imbrication, and lacking latitudinal continuation, record collision stacking basin sediments vertically. Onshore, concurrent uplift and extension are recorded by uplifting strandlines, hanging valleys, and normal faulting, in both continents, and neatly so in the African margin in front of Crete. Joint plate deformation at lithospheric scale is further inferred as wavelengths of relief coherent across both plates. Regions located latitudinally to these collisional sites extrude away obliquely, either rigidly along transpressional systems, as immediately east of Cyprus and Crete, or through flow and halokinesis of Messinian salts, as on the eastern and western sectors of the Mediterranean Ridge. Our evidence typifies incipient lithospheric collision as expressed throughout the East Mediterranean.

How to cite: Fernández-Blanco, D. and R. Ranero, C.: Incipient lithospheric collision throughout the East Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1477, https://doi.org/10.5194/egusphere-egu22-1477, 2022.