THE 2014 MW 6.9 NORTH AEGEAN TROUGH (NAT) EARTHQUAKE: SEISMOLOGICAL AND GEODETIC EVIDENCE

A strong earthquake (Mw 6.9) on 24 May 2014 ruptured the North Aegean Trough (NAT) in Greece, west of the North Anatolian Fault Zone (NAFZ). In order to provide unbiased constrains of the rupture process and fault geometry of the earthquake, seismological and geodetic data were analyzed independently. First, based on teleseismic long-period P- and SH- waveforms a point-source solution yielded dominantly right-lateral strike-slip faulting mechanism. Furthermore, finite fault inversion of broad-band data revealed the slip history of the earthquake. Second, GPS slip vectors derived from 11 permanent GPS stations uniformly distributed around the meizoseismal area of the earthquake indicated significant horizontal coseismic slip. Inversion of GPS-derived displacements on the basis of Okada model and using the new TOPological INVersion (TOPINV) algorithm permitted to model a vertical strike slip fault, consistent with that derived from seismological data. Obtained results are consistent with the NAT structure and constrain well the fault geometry and the dynamics of the 2014 earthquake. The latter seems to fill a gap in seismicity along the NAT in the last 50 years, but seems not to have a direct relationship with the sequence of recent faulting farther east, along the NAFZ

Rupture kinematics of 2020 January 24 Mw6.7 Doǧanyol-Sivrice, Turkey earthquake on the East Anatolian Fault Zone imaged by space geodesy

Here, we present the results of a kinematic slip model of the 2020 Mw 6.7 Doǧanyol-Sivrice, Turkey Earthquake, the most important event in the last 50 yr on the East Anatolian Fault Zone. Our slip model is constrained by two Sentinel-1 interferograms and by 5 three-component high-rate GNSS (Global Navigation Satellite System) recordings close to the earthquake source. We find that most of the slip occurs predominantly in three regions, two of them at between 2 and 10 km depth and a deeper slip region extending down to 20 km depth. We also relocate the first two weeks of aftershocks and find a distribution of events that agrees with these slip features. The HR-GNSS recordings suggest a predominantly unilateral rupture with the effects of a directivity pulse clearly seen in the waveforms and in the measure peak ground velocities. The slip model supports rupture propagation from northeast to southwest at a relatively slow speed of 2.2 km s-1 and a total source duration of ∼20 s. In the absence of near-source seismic stations, space geodetic data provide the best constraint on the spatial distribution of slip and on its time evolution. © 2020 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society

The 23 February 2020 Qotur-Ravian earthquake doublet at the Iranian-Turkish border: Seismological and InSAR evidence for escape tectonics

We present the source mechanisms and rupture processes for the damaging 23 February 2020 earthquake doublet of Mw 5.8 and Mw 5.9 that occurred near the Turkish-Iranian border regions of Qotur-Goharan-Mir'Omar-Ravian (NW Iran), extending towards Saray and Başkale (Eastern Turkey), as obtained from seismological waveform analysis and space geodesy imaging. Seismotectonic characteristics of the sequence highlight the role of indentation tectonics developed within regional-scale compressional environment where the Arabian microplate collides with the Eurasian plate. Here we report optimal finite-fault slip distribution patterns of the 2020 Qotur-Ravian earthquake doublet revealing complex co-seismic rupture propagation along the fault planes with maximum displacements ranging from 20 to 50 cm, stretching from the hypocentre to the surface. Analysis of aftershocks based on 3.5 months-long seismicity confirms distributed deformation. This energetic earthquake sequence demonstrates the distinct rupture characteristics illuminating differences in seismogenic properties and seismic hazard. Coulomb stress transfer modelling predicts triggering of the second event of Mw 5.9 by the first event of Mw 5.8. The zone of Coulomb stress changes attributed to varying pore pressure linking to geothermal water resources in the region as a driving force, may have an impact on the nucleation of triggered faulting. Evaluation of Interferometric Synthetic Aperture Radar (InSAR) data reveals the activated faults with evident co-seismic slip. Specifically, (1) we detected a rare case in earthquake-induced ground deformation where there is overlapping surface deformation due to sequential shallow events located closely in the crust, (2) the initial event ruptured a normal fault located towards W-NW of the latter inferred strike-slip fault and (3) the conjugate system of faults is closely placed at a few km apart. The frequent Sentinel-1 interferograms enhanced our imaging abilities of geometry and kinematics of shallow moderate-size M < 6.0 earthquakes and to trace seismogenic structures in remote and mountainous earthquake prone regions. © 2022 Elsevier B.V

Source Mechanism and Rupture Process of the 24 January 2020 Mw 6.7 Doğanyol–Sivrice Earthquake obtained from Seismological Waveform Analysis and Space Geodetic Observations on the East Anatolian Fault Zone (Turkey)

Here, we present the source mechanism and rupture process for the destructive 24 January 2020 Mw 6.7 Doğanyol–Sivrice earthquake at the East Anatolian Fault Zone (EAFZ, Turkey), obtained from seismological waveform analysis and space geodetic observations. Multi-data analyses and modelling in the present study provide fundamental data and strong constraints for retrieving complex source mechanism of an earthquake and its spatiotemporal slip characteristics along the ruptured segment of fault. The acquired slip model of this earthquake reveals heterogeneous slip distribution along strike N244°E of the fault plane dipping NW (68°) with duration of the source time function (STF) and low stress drop value (Δσ) of ~25 s and ~6 bars, respectively. Back-projection analysis validates fault length (L) stretching along strike for a distance of ~75 km and supports predominant south-westerly bilateral rupture propagation with a variable rupture velocity (Vr) of ~2.3–3.4 km/s along with two main patches, presumably a sequence of two asperities being ruptured following the surface trace of the EAFZ. The distribution of aftershocks based on the analysis of two months long data consistently confirms spreading of seismicity along the ruptured fault. The evaluation of Interferometric Synthetic Aperture Radar (InSAR) data reveals that left-lateral co-seismic slip and significant deformation extends for ~20 km on either side of the fault with evident post-seismic displacement. Yet, no significant vertical offsets were observed as GNSS stations detected only horizontal motions. Coda-wave analysis as an independent tool also confirms moment magnitude of Mw 6.7. Our results highlight a case of a damaging earthquake and enhance our understanding of earthquake mechanics, continental deformation and augmented earthquake risk on the EAFZ. © 2021 Elsevier B.V