Imaging supershear rupture for the 2014 M_w 6.9 Northern Aegean earthquake by backprojection of strong motion waveforms

Abstract

The seismic source spatiotemporal evolution of the Mw 6.9 event on 24 May 2014 in Northern Aegean is imaged by backprojection of strong motion envelopes. The results indicate that the event ruptured on two different fault segments. In the first one, rupture propagated from the hypocenter westward for ∼20 km. In the second delayed segment to the east, rupture propagated eastward for ∼65 km with a supershear velocity (∼5.5 km/s). At the end of this rupture the largest stacking amplitudes are imaged, associated with possible stopping phases from the abrupt cessation of a fast slip. Low‐aftershock seismicity on the supershear segment implies a simple and linear fault geometry there. This is the third large event in the Northern Aegean Trough‐Northern Anatolian Fault zones that has ruptured with supershear speed. This characteristic should be taken into account in studying past events and estimating seismic hazard in this area.

The 2014 Mw 6.9 North Aegean Trough (Nat) Earthquake: Seismological and Geodetic Evidence

“…The slip model shows that rupture propagated along mainly the strike direction of the fault from SW to NE with a slip-vector of 75 o . The waveform fits matches well at all azimuths, and indicative of late moment release seen beyond ~13 s reaching maximum level of displacement which is exceptionally consistent with reported results of strong motion by Evangelidis (2014). We found that the total moment of the finite-fault model is 2.97x10 19 Nm; i.e.…”

“…First, evidence from accelerograms indicates a main shock comprising two sub-events (ITSAK, 2014), as well as the analysis of strong motion data of Evangelidis (2014) indicates a complex fault pattern, comprising two faults, associated with the two distinct clusters of aftershocks 1 and 2 (Figure 1), with the second fault associated with supershear rupture. Although, the single fault pattern obtained from geodetic data ( Figure 5) describes well the data, further analysis assuming a two-fault pattern is in progress and will be presented elsewhere.…”

“…However, it led to some term of panic in the Çanakkale and İstanbul areas, since a possible forthcoming earthquake is expected in the west of the 1999 Kocaeli-İzmit rupture, as a continuation of the westward migrating large earthquakes along the NAFZ since 1939 (Ergintav et al, 2009). The distribution of the aftershocks after the main event (Evangelidis, 2014;NOA, 2014) revealed five clusters of aftershocks ( Figure 1) which correlate with the NAT and seem to cover its major part. The only exception is "cluster 4" which appears somewhat distant from the NAT.…”

“…One characteristic of the seismic sequence is the considerable spread of the zone of aftershocks, extending up to 180km (or even 250km if cluster "4" is included in the seismic sequence). Strong motion recordings suggest that the main shock consisted of two distinct events, separated by a time interval of about ~10s (ITSAK, 2014), while a further study of strong motion data by Evangelidis (2014) concluded that the seismic sequence consisted of two distinct events separated by a 13s interval; the first one correlates with the epicentre, while the second one is characterized by supershear rupture.…”

Focal mechanism determinations of earthquakes along the North Anatolian fault, beneath the Sea of Marmara and the Aegean Sea

“…In 2013, an Mw 5.8 earthquake occurred south of Lemnos Island, south of the main NAF (Kiratzi and Svigkas 2013). Most recently, the 2014 Aegean Sea earthquake (Mw 6.9, Global Centroid Moment Tensor Project, Dziewonski et al 1981;Ekström et al 2012) occurred west of the Ganos fault (Evangelidis 2015). The most recent activity beneath the SOM comparable to these large shocks, however, occurred in 1766 (Ambraseys and Jackson 2000;Meghraoui et al 2012).…”