Displays

The region at the transition from the west to the east Mediterranean is a complex puzzle of terrains spanning in age from the Mesozoic Ionian lithosphere to the Pleistocene arc and back arc domains of the Tyrrhenian system. Although the region has had a complicated evolutionary history, the current configuration of terrains fundamentally denotes Miocene to recent kinematics.

In this contribution we present new data from Tunisia Margin showing the evolution from its formation in early Miocene to recent, the tectonic interaction with the opening of the Tyrrhenian system and its current inversion, and discuss the implications for the regional kinematics evolution.  

The Tyrrhenian is no longer extending, but all basin borders indicate currently active large-scale thrusting  to strike slip tectonics. Tunisia margins formed by a well-know contractional tectonic phase in early Miocene expressed in large-scale tectonics with a clearly imaged thrust  and fold belt, cut by Messinian to Pliocene extensional faulting. However, high resolution multibeam bathymetry and images of the shallowest layers indicates ongoing inversion tectonics.

We compare the tectonic evolution of north Tunisia and Tyrrhenian with the patterns of deformation of the Ionian tectonic wedge observed in new and reprocessed seismic images. We interpret the current deformation of the Ionian tectonic wedge based on the integration of evolution of the kinematics from the data sets of observations from the three systems.

We conclude that the entire region is currently under collision of the Africa Plate with the Adria Plate and the Neogene terrains of the Tyrrhenian Domain.  The corollary is the subduction of the Ionian lithosphere is fundamentally stalled so that the megathrust fault is possibly not any longer accumulating significant shortening and most deformation is currently occurring in steeper faults re-activation or cutting the previous structural framework.

How to cite: Ranero, C. R., Gracia, E., Sallares, V., Grevemeyer, I., and Zitellini, N.: Multiphase tectonic interaction of Tyrrhenian - Tunisia Margin - Ionian systems: Implications for regional seismogenesis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20019, https://doi.org/10.5194/egusphere-egu2020-20019, 2020.

The occurrence of moderate magnitude earthquakes in intermediate depth (40<h<150 km) is a characteristic of the seismicity of the Ibero-Magrebian region. The most important concentration of this activity is in the western part of the Alboran Sea, with the epicenters following an N-S direction. In order to improve the knowledge of the geometry of these seismogenic structures, we have carried out a study of the hypocenters distribution and focal mechanisms for earthquakes that occurred in the period 2000-2020 (M>4.0). For the hypocentral location, we have used a non-linear probabilistic approach (NonLinLoc algorithm) jointly with 3-D lithospheric velocity tomography models recently developed for the Alboran-Betic-Rif zone. Focal mechanisms have been obtained from moment tensor inversion of stations at regional distances (Kiwi tools). Maximum likelihood hypocentres confirm a near vertical N-S distribution in a depth range between 50 and 100 km. Focal mechanisms show a different stress pattern, changing from a vertical tension axis for earthquakes located off-shore and western of 4.5ºW to vertical pressure axis for earthquakes inland and at eastern of 4.5ºW.

How to cite: Buforn, E., Lozano, L., Cesca, S., Cantavella, J. V., Mattesini, M., and Udias, A.: Seismic sources at intermediate depth in the Alboran Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6978, https://doi.org/10.5194/egusphere-egu2020-6978, 2020.

Central Apennines (Italy) is a young and tectonically active mountain chain characterized by a high structural complexity where structures related to various tectonic phases are interacting with each other leading to the reactivation of inherited structures and/or to the segmentation of newly formed ones with a strong impact on the current seismotectonics of the area.

In this context, the surface geological and coseismic observations cannot always be extrapolated straightforward to depth and need to be interpreted in the context of the general upper crustal deformation history.

These considerations apply also to the area struck by the 2016-2018 Central Apennines seismic sequence where the activation of both single faults and complex fault systems has been observed.

In the framework of the RETRACE-3D project, we present a comprehensive 3D geological model derived from the interpretation of a large set of underground data acquired for hydrocarbons explorations and we discuss the implication of this geological reconstruction for the seismotectonics of the area by comparing our results with the coseismic observation.

Our results primarily show that, although the area is currently affected by an extensional tectonic regime, the main architecture of this portion of the chain is still dominated by previous compressional large-scale structures with widespread evidence of segmentation, reactivation and even inversion of various sets of inherited faults.

These results pose new points of discussion on information and input data needed to understand the seismogenesis in young and complex mountain chains, such as the Central Apennines, and strongly impact on the consequent seismic hazard assessment study.

How to cite: Maesano, F. E., Buttinelli, M., Petracchini, L., D'Ambrogi, C., Scrocca, D., Di Bucci, D., Marino, M., Capotorti, F., Cavinato, G. P., Bigi, S., Bonini, L., Mariucci, M. T., Montone, P., Tizzani, P., Castaldo, R., Pepe, S., and Solaro, G.: The upper crustal geological and structural setting in the area of the 2016-2018 Central Apennines seismic sequence. From subsurface modeling to seismotectonics., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19316, https://doi.org/10.5194/egusphere-egu2020-19316, 2020.

In the seismically active region of Central Italy, national (permanent) and local (not-permanent) seismic networks provided very accurate location of the seismicity recorded during the major seismic sequences occurred in the last 25 years (e.g. 1997-1998; 2009; 2016-2017), as well as of the background seismicity registered in the intervening periods.  In the same region, a network of seismic reflection profiles, originally acquired for oil exploration purposes, is also available, effectively imaging the geological structure at depth, to be compared with the seismicity distribution. 

This comparison reveals that, if the position of the brittle/ductile transition exerts a role at regional scale for the occurrence of crustal seismicity, at a more local scale the depth and thickness of the seismogenic layer is mostly controlled by the contrasting rheological properties of the different lithological groups involved in the upper crust. 

The upper crust stratigraphy, including the sedimentary cover and the uppermost part of the basement, consists of alternated strong (rigid, e.g. carbonates and dolostones) end weak (not-rigid, e.g. shales, sandstones, and phyllites) layers. This mechanically complex multilayer is involved in a belt of imbricated thrusts (Late Miocene-Early Pliocene), displaced by subsequent extensional (normal) faults (Late Pliocene-present), responsible for the observed regional seismicity. The top of the basement s.l. (composed of clastic sedimentary and slightly metamorphosed rocks) is involved in major thrusts.  For these different lithological units, combined field and lab studies of fault rock properties have documented localized and potentially unstable deformation occurring in granular mineral phases (carbonates) and distributed and stable slip within phyllosilicate-rich shear zones (shales and phyllites).

By comparing the geological structure with the seismicity distribution, we observed that:

-     The seismicity cut-off (i.e. the bottom of the seismogenic layer) is structurally (not thermally) controlled, and grossly corresponds to the top basement; the upper boundary of the seismogenic layer corresponds to the top of carbonates.

-     Most seismicity occurs within the rigid layers (carbonates and evaporites), and do not penetrate the turbidites and basements rocks.

-      Close to the axial region of the mountain range, where the larger amount of shortening is observed, the presence thrust sheets from the previous compressional phase, significantly affect the seismicity distribution and propagation.

-     Major east-dipping extensional detachments, recognized in the seismic profiles, are also marked by distinctive seismicity alignments.

How to cite: Barchi, M. R., Chiaraluce, L., and Collettini, C.: Lithological and structural control on the seismicity distribution in Central Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10607, https://doi.org/10.5194/egusphere-egu2020-10607, 2020.

On October 25, 2018, at 22:54 UTC, an Mw 6.8 earthquake occurred southwest of Zakynthos island in the Ionian Sea. This is an area with different styles of faulting and the locus of strong events thus ideal for fault interaction studies. The 2018 Zakynthos earthquake was recorded by broad-band and strong-motion networks and provides an opportunity to resolve such faulting complexity. We used waveform inversion and backprojection of strong motion data, partly verified by co-seismic GNSS data, too. The aftershock sequence was relocated, and the moment tensors of the strongest events were evaluated. Stress inversion shows that the region is under sub-horizontal southwest-northeast compression, enabling mixed thrust- and strike-slip faulting. Based on detailed waveform inversion studies, we conclude that the 2018 mainshock consisted of two fault segments: a low-dip thrust, and a dominant, moderate-dip, right-lateral strike slip, both in the crust. This model explains the observed large negative CLVD component of the mainshock. Slip vectors of both ruptured segments, oriented to SW, are consistent with plate motion in the area. The sequence can be explained in terms of trench-orthogonal fractures in the subducting plate and reactivated faults in the upper plate. The 2018 event, and an Mw 6.6 event of 1997, occurred near three localized swarms of 2016 and 2017. Future numerical models of the slab deformation and ocean-bottom seismometer observations may illuminate possible relations between earthquakes, swarms and fluid paths in the region.

How to cite: Sokos, E., Gallovič, F., Evangelidis, C. P., Serpetsidaki, A., Plicka, V., Kostelecký, J., and Zahradník, J.: The 2018 Mw 6.8 Zakynthos, Greece, earthquake – strike-slip and thrust faulting in shallow subduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11007, https://doi.org/10.5194/egusphere-egu2020-11007, 2020.

On 26 November 2019 an Mw6.4 earthquake ruptured along the Adriatic coast of Albania causing extensive destruction, mainly in Durrës city and Thumanë town, claiming 51 human lives. Maximum intensity in both areas reached the level of VIII-IX. On 21 September 2019 a strong foreshock (Mw5.6) occurred at nearly the same epicenter causing considerable damage. Fault-plane solutions of the main shock showed reverse faulting striking NW-SE and likely dipping to east indicated by the regional tectonics. In the long-term sense the earthquake has not been a surprise since the area experienced destructive earthquakes in the past as well. We present observations collected during a post-event field survey as well as a seismic source model of the main shock. Apart from the strong motion and amplification phenomena due to loose soil conditions and soil liquefaction, the severe building damage is attributed to the synergy of several other factors including poor workmanship and construction quality, ageing of materials, impact of the September 21^st earthquake and pre-existing stress on buildings suffering differential displacements due to soft soil conditions in their foundations. A finite fault model was developed from the inversion of 30 teleseismic P-wave records following the methodology by Hartzell and Heaton (1983, 1986). The hypocenter was manually located offshore but close to Durrës at depth of ~22 km using the NLLoc procedure and the Ak135 velocity model based on 71 seismic phases at distances ≤550 km. Based on this solution a rectangular fault was assumed of 29 km in length with a depth ranging from 15 to 27 km which is large enough to describe successfully the slip for an earthquake of M_w=6.4. A kinematic parameterization of the earthquake fault was used to identify the space-time distribution of slip. Synthetics were calculated for each cell in which the fault is divided and are compared with the recorded data during an inversion producing the solution vector, i.e. the slip for each cell. Strike of 345° and dip of 22° were found to better fit the data. The rake vector was allowed to vary within the range from 65° to 155° permitting up-dip and possible left lateral strike-slip movement of the hanging wall domain relatively to the footwall. Rupture velocity was allowed to vary from 2.4 km/s to 3.6 km/s, the best fit found for 2.6 km/s. The heterogeneous spatial slip distribution obtained shows a complex rupture process with maximum slip at the source of ~1.5 m with the rake vector at that point being of 115° but an arithmetic mean of the rake for the cells with significant slip over 10 cm is 99°. This implies that the thrust component is the one that played the important role in the rupture process. Significant values of slip were also found in a second patch in the northern area of the fault at depths from 19 to 26 km. The total duration of rupture was nearly 16 s, while the total seismic moment released was M_o=5.0x10¹⁸ N*m, corresponding to M_w=6.4.

How to cite: Papadopoulos, G., Agalos, A., Carydis, P., Lekkas, E., Mavroulis, S., and Triantafyllou, I.: The Destructive Earthquake (Mw6.4) of 26 November 2019 in Albania: a First Report, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20749, https://doi.org/10.5194/egusphere-egu2020-20749, 2020.

During the ODEMAR 2013 and SUBSAINTES 2017 cruises we mapped the full extent of the seafloor rupture associated with the 2004 Mw 6.3 Les Saintes extensional earthquake. Near-bottom bathymetry acquired both with ROVs and AUVs along the Roseau Fault reveal a normal fault scarp developing in an extensional graben within the Caribbean volcanic arc, between the islands of Guadeloupe and Dominica. Optical inspection during ROV dives along the scarp’s base, where fault mirrors are well-preserved, allowed us to identify and characterize the coseismic fault rupture, and measure the coseismic displacements using both laser calipers and measurements performed on video-derived, textured 3D models, with accuracies better than 1 cm.

The 2004 rupture extends ~20 km along the Roseau Fault, with a vertical displacement exceeding 2.5 m at its center, and tapering towards its ends. Local variations in apparent fault slip within a single 3D model (fault lengths of ~10 to 300 m) document local deposition of gravity debris cones at the base of the scarp, extending laterally between a few to tens of m, and covering the coseismic markers. Gullies eroding the footwall and depositing debris cones on the hanging wall do not show any significant displacement. Fault scarps on either side of the gully mouth instead record significant displacements, suggesting that either erosion or deposition along the gully bottom efficiently obliterated markers of coseismic deformation.

We inspected all overlapping seafloor imagery acquired in December 2013 and April 2017, >10 years after the 2004 Les Saintes earthquake, extending laterally over >3 km of the Roseau Fault rupture.  Neither the bed of gullies crossing the rupture, nor the debris and rubble at the base of the fault scarp show any noticeable seafloor change indicating mass wasting and transport, and only changes in mobile sediment (e.g., ripples) can be detected between both image sets.  We identified a single area, ~2m wide, with apparent deposition of pebbles during these 3.25 years period, and associated with a local mass-wasting event.

These observations point towards a systematic triggering of mass-wasting during seismic events, with deposition of rubble and rocks both at dejection cones at the mouth of gullies, or at the base of fault scarp sections displaying fault mirrors, covering or obliterating the coseismic markers. Therefore, long-term erosion and deposition processes here are gravity-driven and triggered by the history and magnitude of seismic events. Similar seismic controls may enable denudation of exposed oceanic lithosphere at fault scarps developing along and flanking mid-ocean ridges.

How to cite: Escartin, J., Billant, J., Leclerc, F., Olive, J.-A., Istenic, K., Gracias, N., Garcia, R., Arnaubec, A., Deplus, C., and Feuillet, N. and the SUBSAINTES Science Party: Connecting seismicity, gravity-driven erosion and deposition at submarine normal faults: Insights from mapping of the 2004 Mw 6.3 Les Saintes earthquake rupture (French Antilles), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12848, https://doi.org/10.5194/egusphere-egu2020-12848, 2020.

The Castelluccio basin in the central Apennines (Italy) is a ~20-km²-wide intramontane Quaternary depression located in the hangingwall of the NW-trending and SW-dipping Vettore-Bove normal fault system (VBFS). This system is responsible for the 2016-2017 seismic sequence, culminated with the 30 October 2016 Mw 6.5 Norcia earthquake that caused widespread surface faulting affecting also the northern part of the Castelluccio basin. Available borehole and geophysical data are not enough to constrain the basin structure, infill architecture and their relations with the long-term activity of the VBFS. Therefore, we carried out an extensive 3D survey using the innovative Fullwaver (FW) technology, conceived to perform deep electrical resistivity tomography (DERT). We aimed at: a) mapping the geometry of the pre-Quaternary limestone basement and the basin infill thickness down to a depth of ~1 km; b) mapping the subsurface structure of known faults and their extent underneath the alluvial cover; c) mapping possible blind faults splays.

The 3D survey covered a 23 km² area and it was designed with the aim to map the region as regularly as possible, taking into account the rugged topography and logistic issues. We used a series of independent 2-channels receivers connected each to three grounded steel electrodes, 200 m spaced, to record the electrical field generated by a five kilowatt current regulated Time Domain Induced Polarization transmitter. Data were modelled with ViewLab software via a regularized inversion with smoothness constraints to cope with the expected subsurface strong resistivity changes, and to obtain a robust 3D resistivity model.

The FW technology allowed us to constrain the geometry of the basin. The infill material is imaged as a wide, N-trending moderately resistive (< 300 Ωm) to conductive  (< 100 Ωm) region, likely made of silty sands and gravels, deepening down to 500 m b.g.l. in the southern sector, suggesting the occurrence of two main depocenters. All over the basin, we identify paired high-resistivity (> 500-1000 Ωm) and low-resistivity (< 400 Ωm) belts related to the limestone basement and to the basin infill, respectively. They display NNE and NNW dominant trends. We interpret the sharp boundaries of NNE-trending belts as related to early extensional faults promoting the basin inception. The NNW-trending belts suggest the occurrence of faults that locally cross-cut the previous ones, and that we interpret as splays of the VBFS buried under the basin sedimentary cover. The recognition of different systems of extensional faults is coherent with results of high-resolution seismic profiling carried out recently in the basin. A high-resolution 2D transect with 15 m-spaced electrodes across the 2016 surface ruptures shows details of the active VBFS splay down to 300 m depth. Moreover, in the eastern sector of the survey area, low-resistivity round-shaped anomalies in the Mesozoic substratum hints for deep Miocene compressional structures. Therefore, our DERT imaging suggests a complex tectonics in the subsurface of the Norcia earthquake fault. In particular, the currently active NNW-trending faults seem to overprint a pre-existing structural framework, promoting fault segmentation at different spatial scales

How to cite: Sapia, V., Villani, F., Fischanger, F., Lupi, M., Baccheschi, P., Brunori, C. A., Civico, R., Coco, I., De Martini, P. M., Giannattasio, F., Improta, L., Materni, V., Murgia, F., Pantosti, D., Pizzimenti, L., Pucci, S., Ricci, T., Romano, V., Sciarra, A., and Smedile, A.: A deep resistivity Full Waver survey unravels the 3D structure of the Castelluccio basin in relation to the source of the 2016 Mw 6.5 Norcia earthquake (central Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21933, https://doi.org/10.5194/egusphere-egu2020-21933, 2020.

Active deformation in the Central Apennines is mostly accommodated by NW-SE normal faults systems that produce moderate to large earthquakes at shallow depth. Recent examples include the 1915 Mw≈7 Avezzano earthquake (Fucino basin) and the 2009 Mw=6.1 L’Aquila earthquake (Aterno basin) which were both associated with major loss of life and massive damage to buildings and infrastructure. Here, we study the 40-km-long Ovindoli – Piano di Pezza – Campo Felice – Monti d’Ocre (OPCM) fault system, a major NNW-SSE system that potentially links the Fucino and the Aterno fault-systems. The OPCM exhibits linear and arcuate sections with four main segments and borders the eastern margin of the Aterno basin. Paleo-earthquake rupture data on the Piano di Pezza (PPF) and Campo Felice (CFF) faults exhibit remarkable synchronicity with the Fucino fault system, with the most recent surface-rupturing earthquake likely occurring in the XIV^th century. In order to better understand the relationships between and earthquake rupture scenarios, we focus on the basin geometry and fault surface expression of the Piano di Pezza fault combining geomorphology and subsurface geophysics. We map the fault trace with unprecedented detail using terrestrial laser scanner surveys and quantify surface deformation affecting alluvial fans as well as glacial moraines. We obtain a mean vertical offset of 2.5 m +/- 0.3 m for the most recent features, well in agreement with paleoseismological data. Furthermore, we document slip distributions at different time scales along strike with a maximum value at the connection between the PPF and the OF. Beneath the scarp, geophysical data reveal a complex faulting geometry with several parallel strands and two minor blind splays. Electrical resistivity tomography images show a cumulative vertical offset of ~ 15 m affecting an interface attributed to the Last Glacial Maximum and confirm the high vertical slip across the fault zone. Gravimetric anomalies across the basin also indicate the sedimentary fill has recorded a maximum finite cumulative throw of the PdP fault system of 110-140 m. This suggests a maximum vertical slip rate of 0.2-0.3 mm/year since the Pleistocene, which contrasts with the high post-LGM slip rate estimated from trenches. Overall, our observations suggest that the arcuate PPF originally formed as a reverse fault during the Mio-Pliocene compressive stage and is now reactivated as an extensional horsetail-like feature by ruptures along a major strike-slip fault (OF). This finding points to the PPF as mostly built through ruptures along the OF leaking onto an inherited structure. The time-varying slip rates may also denote an episodic behavior marked by short periods of high seismic activity (a few centuries) and long intervals of seismic quiescence (a few millennia). Furthermore, possible earthquake rupture scenarios along the OPCM may encompass the whole OPCM fault system (cumulative length ca. 40 km) or rupture termination along the PPF (cumulative length ca. 15-20 km) with significantly different impacts over the populated Fucino and Aterno basins.

How to cite: Ferry, M., Gautier, S., Mazzotti, S., Villani, F., Stell, E., Jacottin, M., Pantosti, D., Sapia, V., Ricci, T., Benedetti, L., Di Giulio, G., and Vassallo, M.: Structure and segmentation of the Ovindoli – Piano di Pezza – Campo Felice fault system (Central Apennines, Italy): Evolution and reactivation of inherited faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7362, https://doi.org/10.5194/egusphere-egu2020-7362, 2020.

The Western Calabrian margin (Italy) is the most active segment of the Apennine back-arc system, formed in response to the slow Africa – Eurasia convergence. The offshore area represents the transitional region between the arc and the back-arc: it is affected by several fault systems, most of them able to trigger highly destructive earthquakes. Indeed, the Calabria and its western offshore are characterized by the highest seismic moment release of the entire Apennines, also evidenced by historical seismicity catalogue, the most accurate over the world. During last decades, scientific community invested huge resources in assessment of seismic and tsunami hazards. Furthermore, during last years several local-scale works allowed of improving knowledge of the faults geometry, magmatism, seismogenic and tsunamigenic potential along the western offshore region (Loreto et al., 2017; Brutto et al., 2016; De Ritis et al., 2019). Some active faults, belonging to NE-SW-trending normal fault systems accommodating the inner-arc collapse related to slab-decupling, are also responsible of the most destructive historical sequences, still to be adequately characterized. Using vintage SPARKER 30 Kj acquired in the seventies and recent multichannel seismic profiles together with middle resolution morpho-bathymetric data we produced a new tectonic map of the Calabria back-arc system. Further, we characterized some before-unknown faults and linked them with shallow structures, as ridges and slumps / slides. This area seemingly less populated of faults compared to the peri-Tyrrhenian margin, where several faults belong to different systems, i.e. (i) the rifting system active that allowed the opening of the Tyrrhenian Basin and (ii) the slab-decupling related normal faults system currently active. The comparison with historical and instrumental seismicity allowed us to highlight possible seismic gaps that, if considered, could strongly improve the map of seismogenic potential of the Tyrrhenian back-arc system.

Bibliography

Brutto, F. et al. (2016). The Neogene-Quaternary geodynamic evolution of the central Calabrian Arc: A case study from the western Catanzaro Trough basin. Journal of Geodynamics, 102, 95-114.

Loreto, M. F. (2017). Reconstructed seismic and tsunami scenarios of the 1905 Calabria earthquake (SE Tyrrhenian sea) as a tool for geohazard assessment. Engineering geology, 224, 1-14.

Tripodi, V. et al. (2018). Neogene-Quaternary evolution of the forearc and backarc regions between the Serre and Aspromonte Massifs, Calabria (southern Italy). Marine and Petroleum Geology, 95, 328-343.

How to cite: Palmiotto, C., Loreto, M. F., Muto, F., Ferrante, V., Pettenati, F., Sandron, D., and Tripodi, V.: Faults distribution and seismogenic potential in the Calabrian back-arc domain, SE Tyrrhenian Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19590, https://doi.org/10.5194/egusphere-egu2020-19590, 2020.

The Calabria Arc (CA) is the narrowest subduction-rollback system on Earth, and it has been struck repeatedly by destructive historical earthquakes often associated with tsunamis. In spite of the detailed earthquake catalogue, the source parameters of most historic earthquakes are still debated, especially for earthquakes that may have been generated offshore.

The subduction system is characterized by an irregular plate boundary reflecting the presence of continental blocks, indenters, and different rates of continental collision. Convergence between Eurasia and Africa produces both compressive and transtensional deformation in the offshore accretionary complex. Shortening occurs along the outer deformation front and along splay faults accommodating differences in rheology and basal detachment depth. Two oppositely dipping strike-slip/transtensional fault systems, i.e., the Ionian (IF) and Alfeo-Etna (AEF) faults produce deep fragmentation of the subduction system and the collapse of the accretionary wedge, in agreement with geodetic models suggesting plate divergence in this region. Transtensional lithospheric faults segmenting the subduction system are punctuated by mantle-rooted diapirism driven by arc orthogonal rifting, collapse of the accretionary wedge, and deep fragmentation of the subduction system along pre-existing Mesozoic transform faults.

Seismological observations in the Western Ionian Sea highlight the presence of earthquake clusters along wide and deep-seated active tectonic structures, which were proposed as likely seismogenic sources for large magnitude historic earthquakes/tsunamis in the region. Low to moderate magnitude earthquakes occurring offshore were relocated using a new 1D velocity model for the Ionian Sea, constrained by geological and geophysical observations, which included data collected by NEMO-SN1 seafloor observatory. Seismological data from NEMO-SN1 were integrated with observations carried out by over 100 land stations of the INGV network, and led us to compile a map of 3D distribution for over 2600 events. 3D locations and focal mechanism analyses allowed us to highlight local lithospheric structure. Although seismicity appears scattered in a wide corridor of deformation within the subduction system, we observe alignments of events along main fault systems with strike-slip and extensional mechanisms. Moreover, results from seismological data analysis, i.e., misfits in the 3D distribution of hypocenters and tomographic maps, could be explained by the presence of an anomalous area between the two structures, characterized by thinned lithosphere probably caused by incipient rifting, as suggested by seismic reflection images and geodynamic interpretations.  

How to cite: Polonia, A., Tiziana, S., Andrea, A., Graziella, B., Andrea, B., Luca, G., and Luigi, T.: Active tectonics and seismicity in the Calabrian Arc subduction complex (Ionian Sea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13032, https://doi.org/10.5194/egusphere-egu2020-13032, 2020.

On November 26, 2019, a strong earthquake (Mw6.4) occurred about 16 km, north of the Durresi city in the Adriatic Sea, and 35 km NW from the capital city of Tirana, in the western part of Albania. The main shock of November 26 at 15:20 (UTC) was followed by a great number of aftershocks.
The main event is not a shallow one, with the hypocentral depth at 39 km. This fact explains the localized destruction, not only in the epicentral zone but in a larger zone. This earthquake expresses the increase of recently seismic activity of the Adriatic seismogenic zone. The main shock has caused cracking of the earth, especially in the region where the epicenter of the earthquake is located. The largest cracks are in the vicinity of the Erzen river estuary.
These cracks have widths ranging from few cms to 1m and extending from several hundred meters to 1 km. The depth of cracking in some cases reaches into 2 meters. Those cracks are numerous and often create parallel systems between them that follow the current river bed or traces of the old river beds (paleoalvei).
Liquefaction phenomena have been observed extensively in the area between the villages of Juba and Hamallaj. In this area, there have been observed outflows of pressure water associated with sand and clays. The height of the water has often reached up to 1 meter around the water wells. The phenomenon of liquefaction in these areas has been associated with soil cracks of several cms wide and several tens of meters long.
Based on the neotectonic mapping and the focal mechanism of the mainshock, strike 219°, dip 40°, rake -90°, it is considered that the seismotectonic source that generated thisearthquake is related to NW-SE longitudinal tectonic of the Adriatic Sea. Based on the focal plane solutions provided by the IGEWE website, the mainshock was generated by the activation of an NW-SE striking thrust fault with the compression axes in the NE-SW direction.

Sea Adriatic neotectonic extend from Dalmatic coast to Ionian coast is an ancient tectonic, a reverse fault thrust, thus activated during the Quaternary geologic period to the present day, occasionally with strong earthquakes. The seismic movement has also caused a 10 cm elevation of the terrain in the epicenter of the earthquake, which has been accompanied by a coastline retreat in this area (Hamallaj beach).
The 21 September and 26 November 2019 earthquake sequences, as well as the 1926 seismic event that took place in the Durresi region, exhibit a rough NW−SE-trending structure, which is an active seismotectonic zone in western Albania, therefore constituting a threat for nearby urban areas.

How to cite: Ormeni, R., Hoxha, I., Naco, P., and Gego, D.: The strong earthquake of 26 November 2019 (MW6.4) and its associate active tectonic of Durresi Region in Albania., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6096, https://doi.org/10.5194/egusphere-egu2020-6096, 2020.

On November 26, 2019, an earthquake struck the central western part of Albania. It was assessed as Mw 6.4. Its epicenter was located offshore northwestern Durrës, in a distance of about 7 km north of the city and 30 km west from the capital city of Tirana. Its focal depth was about 10 km. Based on the focal plane solutions provided by several seismological institutes and observations, the mainshock was generated by the activation of a NW-SE striking reverse fault. Unfortunately, the earthquake claimed the lives of 52 people. Few hours after the mainshock, the authors visited the earthquake affected areas in order to conduct a field macroseismic survey and geological reconnaissance for assessing the earthquake impact on the building stock. The dominant buildings in the affected area are buildings with load bearing solid brick walls and concrete floor slabs, precast concrete panel buildings and buildings with reinforced concrete (R/C) frame and infill and partition walls. The main characteristic in the majority of these structures is the presence of prefabricated concrete floor slabs with width of 0.7-1.0 m and no connections between them. Building damage was distributed along two ellipses, whose major axis is oriented generally NW-SE. The western ellipse of major damage was observed in Durrës city, located within the Periadriatic Depression, and the eastern one in Thumanë, Laç, Fushë-Krujë, Kamëz towns and Tirana city along the eastern margin of the Tirana Depression. This NW-SE orientation coincides with the strike of the seismogenic fault as it is derived from the fault plane solutions. The first building type presents slight non-structural and structural damage in Durrës city. However, buildings of this type in Thumanë suffered very heavy structural damage including partial collapse resulting in many fatalities. The second type did not suffer significant non-structural or structural damage. The majority of the observed R/C multistorey buildings in Durrës suffered damage to the lower three to four storeys, while the above storeys remained intact. Damage is attributed to the soft soils in the earthquake-affected areas, the undesired resonance phenomena in high buildings, the large duration of the earthquake shaking, the shallow water table in coastal and swamp areas, the pre-existing stress of buildings founded on soft soils characterized by differential settlements and possible liquefaction phenomena, the poor construction quality and workmanship of the affected buildings, the interventions made, the ageing of materials due to differential displacements of the foundation soil, the applicable antiseismic regulations of the time, if ever were applied, the lack of maintenance and inadequate repair after previous destructive earthquakes and the impact of the September 21, 2019 Mw 5.6 earthquake on the buildings of the affected area. The damage are considered typical of an earthquake of this magnitude. The effect of the previous September 21, 2019 Mw 5.6 earthquake in the same area should be also taken into account. Based on the seismic zonation map of Albania, it is concluded that the resulted intensities from the 2019 earthquake are within the limits specified in the Seismic Zonation Map.

How to cite: Mavroulis, S., Lekkas, E., Carydis, P., and Papa, D.: Factors controlling building damage distribution of the November 26 Mw 6.4 Albania earthquake , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18616, https://doi.org/10.5194/egusphere-egu2020-18616, 2020.

We identify the main source of the M6.4 earthquake that rocked north-central Albania on November 26, 2019 to be located within the frontal area of the basal thrust of the Dinaric-Hellenic orogen. This earthquake was easily felt some 400 km away and was the strongest to affect the eastern Adriatic coast since the M7.1 event that struck Montenegro in 1979. Already two months earlier on Sept 21-22, several M5 earthquakes hit the same area. According to the USGS and EMSC-CSEM, all 2019 events occurred within a c. 40km wide epicentral area extending along strike of the front of the northernmost Hellenides between the city of Durres to offshore of the town of Lezhë. A depth interval of 10-20 km was poorly constrained for these events, with hypocenters located below the Periadriatic Foredeep Basin made up of deformed and poorly consolidated Neogene and Pleisto-Holocene sediments. For the M6.4 event, InSAR images from the Sentinal-1 satellite indicate up to 7 cm of epicentral uplift and a centroid depth of c. 17 km for the M6.4 event.

By combining own onshore geologic mapping with previously published subsurface imaging of the top of the pre-Neogene carbonates across the convergent margin, we have identified structures associated with a large ENE-dipping blind thrust forming the base of the Neogene-to-Present accretionary wedge at the front of the northernmost Hellenides belt. The centroid depth for the M6.4 event is interpreted to lie within this basal thrust; the shallower Sep 21 M5.6 event is inferred to lie at the western end of this same thrust, which does not appear to break the surface in offshore sections. Taken together, these events point to seismic slip on a thrust plane dipping some 30° ENE.

According to geological data this thick frontal Neogene thrust wedge is not continuous across the Dinaride-Hellenides junction, but is dextrally offset in northern Albania by the Lezhë Transfer Fault that forms the northern boundary of the epicentral area activated in 2019. NE of the Lezhë Fault in northernmost Albania and Montenegro, Neogene shortening perpendicular to the orogenic front is minor (≤ 10 km) in industrial seismic sections, whereas to the SW, a Neogene displacement of ≥ 100 km is determined from offset Triassic salt layers in the footwall and hangingwall of the basal thrust. The Lezhë Transfer Fault is thus interpreted to have accommodated a sudden increase of Neogene shortening along the orogenic front to the SSW. Onshore mapping indicates that this fault also transfers onshore Neogene clockwise bending of the Hellenides with respect to the Dinarides of Montenegro. It kinematically links the offshore orogenic front in the SSW to thrusting and orogen-parallel extension along th Shkoder-Peja Normal Fault in the hinterland of the coastal area. Our work suggests that seismic rupture is segmented along the Dinaride-Hellenide front, with the M6.4 Albanian and earlier M7.1 Montenegrinian events occurring in structurally and kinematically separate domains.

How to cite: Handy, M. R., Schmid, S. M., and Briole, P.: The M 6.4 Albanian earthquake of Nov. 26, 2019 and its relation to structures at the Dinarides-Hellenides junctions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5409, https://doi.org/10.5194/egusphere-egu2020-5409, 2020.

At 3:54 night time on November the 26th the city of Durres in Albania was hit by an earthquake of Mw 6.2, followed in the next 4 hours by three additional earthquakes with Mb > 5.0. These earthquakes, part of a sequence that continued with much reduced intensity until mid December, caused severe damages in Durres and the adjacent region, counting a final human toll of about 50 casualties and over 2000 injuried. The historical catalogues show that Albania has been affected by over 10 relatively strong earthquakes (Mw> = 6.0) in the last 200 years (Kiratzi and Dimakis 2013), testifying to an important seismic history.

The focal mechanisms of the Durres earthquakes show compressive fault planes placed at ca. 10 km depth. These earthquakes are part of a belt of compressional earthquakes that borders to the east the southern Adriatic, including the strong Montenegro earthquake (Mw 7.1) of April 1979, indicating that shortening is currently ongoing at the front of the southern Dinarides and Hellenides.

The geological structure of Albania, at the junction between the Dinarides and the Hellenides, shows structural complexities that have their roots in the Mesozoic paleogeography of the region (Argnani, 2013). The front of the Albanian fold-and-thrust belt extends to the sea, where it has been studied thanks to some seismic acquisition campaigns aimed at investigating the geology of the Adriatic Sea (Argnani 2013). This sector of the thrust front is characterized by the presence of important back thrusts, which are correlated to the spatial distribution of the Mesozoic domains of carbonate platforms and pelagic basins. In the sector facing the southern Adriatic basin the presence of a large thickness of Oligocene-Quaternary clastic sediments filling the foredeep promotes the development of triangle zones and backtrusts. The basal thrust of the triangle zone system affects Mesozoic carbonates at an estimated depth of 10-15 km (Fantoni and Franciosi, 2010) and appears to be the source of the Durres earthquakes. A similar structural setting can be envisaged for the Montenegro earthquake of 1979, as the offshore structures show a continuity, although a substantial change in strike occurs across the trend of the Shkoder-Peja line. A large lateral displacement of the internal units occurs along the Shkoder-Peja transversal line, which marks the junction between the Hellenides and the Dinarides. The shallow water limestones of the more external Kruja domain, however, are not laterally offset. Palaeomagnetic results indicate that the Miocene-Pliocene clock-wise rotation of the western arm of the Aegean opening was accomplished just south of the Shkoder-Peja line; these rotations impose an overall change in strike of the outer thrusts, although the frontal structures are specifically affected by the nature of the Mesozoic domains entering the thrust system.

References

Argnani A. (2013) -. Ital. J. Geosci., 132, 175-185.

Fantoni R., Franciosi R. (2010) - Rend. Fis. Acc. Lincei 21, S197–S209.

Kiratzi A., Dimakis E. (2013) - Ital. J. Geosci., 132, 186-193.

How to cite: Argnani, A.: The Durres earthquakes of November 2019: A geological perspective from the Adriatic offshore, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17895, https://doi.org/10.5194/egusphere-egu2020-17895, 2020.

On 26^th of November 2019 an M_w 6.4 earthquake ruptured near the port town of Durrës, only 25 km from Tirana, the capital of Albania. It caused major damage and killed 51 people, making it the deadliest earthquake in 2019 worldwide.

The earthquake occurred on the eastern Adriatic margin, where the Adriatic micro-plate collides with Eurasia causing widespread distributed deformation and crustal shortening that built the peri-Adriatic orogenic belts. Convergence is accommodated in the external Dinarides/Albanides by thrust faulting, mostlyalong E-dipping low-angle detachments with subordinate W-dipping back-thrusts in the most external thrust belt segment. The deformation front, particularly along the southeastern Adriatic coast, is seismically highly active, manifested not only by this most recent event, but also, e.g., by one of the largest instrumentally recorded earthquakes in Europe, the 1979 M7.1 Montenegro event slightly further north and a number of disastrous historic earthquakes.

The 2019 Durrës mainshock was apparently relatively deep (~25 km) and of thrust type. It was preceded by significant foreshock activity starting in September 2019 with two M_w 5.6 and 5.1 earthquakes a few kilometres south of the mainshock that also had a thrust mechanism, however with nodal planes differing from the mainshock, indicating that these occurred on a different fault.

Approximately two weeks after the mainshock, we installed a 30-station short-period seismic network to densely cover the epicentral area. We will present a preliminary analysis of the mainshock and its aftershock sequencehopefully elucidating the fault network responsible for the earthquake sequence.

How to cite: Dushi, E., Schurr, B., Kosari, E., Soto, H., Gjuzi, O., Rohnacher, A., Haberland, C., Rietbrock, A., Tilmann, F., Handy, M., Koci, R., Ustaszewski, K., Dahm, T., Meier, T., and Duni, L.: The 2019Durrës, Albania earthquake sequence – preliminary results from a post-seismic campaign, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22189, https://doi.org/10.5194/egusphere-egu2020-22189, 2020.

From July 2016 to May 2017, we deployed a local seismic network composed of 15 short-period seismic stations to investigate the ongoing seismotectonic deformation of Western Greece with emphasis on the region between Ambrakikos Gulf (to the north) and Kyparissia (to the south). The network was deployed to investigate the behavior of key crustal blocks in western Greece, such as the Ionian-Akarnania Block (IAB).

After applying automatic P- and S- wave phase picking we located 1200 local earthquakes using HypoInverse and constrained five 1D velocity model by applying the error minimization technique. Events were relocated using HypoDD and 76  focal mechanisms were computed for events with magnitudes down to M_L 2.3 using first motion polarities.

We combined the calculated focal mechanisms and the relocated seismicity to shed light on the IAB block boundaries. Three boundaries highlighted by previous studies were also evidenced :

-The north-west margin of the block, the Cephalonia Transform Fault, Europe‘s most active fault. NW-striking dextral strike-slip motion was recognized for this fault near the Gulf of Myrtos and the town of Fiskardo.

- The south-east margin is the Movri-Amaliada right-lateral Fault Zone, activated during the Movri Mt. M_w 6.4 earthquake sequence.

- The Ambrakikos Gulf (a young E-W rift) and the NW-striking left-lateral Katouna-Stamna Fault zone depict the north and north-eastern margins of the IAB block.

Seismicity lineaments and focal mechanisms define theKyllini-Cephalonia left-lateral fault, which is also highlighted by bathymetry data. We interpret this fault as the south-western margin of IAB separating an aseismic area observed between Cephalonia and Akarnania from a seismogenic zone north of Zakynthos Island and bridging NW Peloponnese with Cephalonia.

How to cite: Haddad, A., Ganas, A., Kassaras, I., and Lupi, M.: Seismotectonics of the Ionian-Akarnania Block (IAB) and Western Greece deduced from a local seismic deployment., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21285, https://doi.org/10.5194/egusphere-egu2020-21285, 2020.

Geodetic and seismic moment-rates comparison provides significant insights into the seismic hazard of regions subjected to relevant crustal deformation. We performed such a comparison for the Aegean-Anatolian region, marking the collision zone between the African, Arabian and Eurasian plates, and characterized by a complex tectonic evolution. First we provided an improved description of the ongoing crustal deformation field of the Aegean-Anatolian region, based on an extensive combination of novel observations rigorously integrated with the published GNSS-based geodetic velocities. Then, the geodetic velocity field is used as model input to estimate the 2D strain-rate and moment-rates fields over a geographic 1° x 1° grid. Second, we collected the historical and instrumental earthquake data in order to define the long-term moment release rate by adopting a truncated Gutenberg-Richter relation. Finally, the geodetic and seismic moment-rates comparison allowed to differentiate crustal deformation modality (seismic versus aseismic), as well as to highlight seismic cycle gaps over the investigated region.

How to cite: Sparacino, F., Galuzzi, B. G., Palano, M., Segou, M., and Chiarabba, C.: The Aegean - Anatolian region: insights on seismic hazard from geodetic and seismological observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19127, https://doi.org/10.5194/egusphere-egu2020-19127, 2020.

Paleomagnetic mapping has beenapplied mainly for investigation of two types of regions: (1) platform areas, and (2) World Ocean. Conventional paleomagnetic mapping has been methodologically formed as the problem of identifying the bedding conditions of magnetostratigraphic units of sedimentary strata of the predominantly platform regions. It is uses mainly paleomagnetic laboratory data analysis derived from field studies. Employing completely different methodological principles, paleomagnetic maps of the Earth's basaltic crust of the World Ocean were constructed. These maps have not only geophysical but also geodynamical and structural-tectonic significance.

The most complex regions of the Earth are the areas of transition from the ocean to the continent, as well as the spreading and collision zones of lithospheric plate joining. Here the most diverse manifestations of the structures and movements of the earth's crust and upper mantle and various and multiphase magmatic appearances are developed. The Eastern Mediterranean, which is a striking example of such regions, is located in the junction between the two largest Earth's lithospheric segments: Eurasia and Gondwana.

The paleomagnetic mapping of transition zones from the ocean to the continent was only sporadic and was not methodologically and rigorously developed as the mapping of continental and oceanic platforms. For more than 20 years of research experience in the Eastern Mediterranean region, we have been able to develop a comprehensive methodology for tectono-paleomagnetic mapping of transition zones from ocean to the continent (e.g., Eppelbaum and Katz, 2015). These reconstructions were utilized as a basis for identifying a variety of mapped bodies and structures. The methodology is based on the integration of the mapping techniques for both continental and oceanic platforms: paleomagnetic reconstructions, results of radiometric dating of magnetically active rocks, biogeographical studies, satellite data examination, plate tectonic reconstructions and utilization of results of various geophysical surveys. All these data are used for combined identifying mapped geological bodies and structures.

Tectonic-paleomagnetic mapping as a new type of geological and geophysical surveys contributed to an essential amendment in understanding the nature and structure of the Eastern Mediterranean. It turned out that this is not a passive, but an active continental margin, where the Mesozoic terrane belt is developed. This belt includes tectonic units of the thinned continental crust and parts of the Neotethys Ocean crust with a block of the ancient Kiama hyperzone (Early Permian) and a series of ophiolite bodies and sporadic mantle diapirs (Eppelbaum and Katz, 2015).

Tectonic-paleomagnetic mapping reveals not only the historical-geodynamic, but also the deep-geophysical nature of the Eastern Mediterranean evolution. In particular, it was established that in the formation of the Sinai plate, two zones with the deep mantle trap complexes were involved: the Late Mesozoic and the Late Cenozoic relating to the Jalal and Sogdiana paleomagnetic hyperzones, respectively.

Eppelbaum, L.V. and Katz, Yu.I., 2015. Paleomagnetic Mapping in Various Areas of the Easternmost Mediterranean Based on an Integrated Geological-Geophysical Analysis. In: (Eppelbaum L., Ed.), New Developments in Paleomagnetism Research, Ser.: Earth Sciences in the 21st Century, Nova Science Publisher, NY, 15-52.

How to cite: Eppelbaum, L. and Katz, Y.: Tectono-paleomagnetic mapping of transition zones from ocean to continent (on example of the Eastern Mediterranean), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2049, https://doi.org/10.5194/egusphere-egu2020-2049, 2020.