Περίληψη:
Significant seismicity anomalies preceded the 25 October 2018 mainshock (Mw = 6.8), NW Hellenic Arc: a transient intermediate‐term (~2 yrs) swarm and a short‐term (last 6 months) cluster with typical time‐size‐space foreshock patterns: activity increase, b‐value drop, foreshocks move towards mainshock epicenter. The anomalies were identified with both a standard earthquake catalogue and a catalogue relocated with the Non‐Linear Location (NLLoc) algorithm. Teleseismic P‐waveforms inversion showed oblique‐slip rupture with strike 10°, dip 24°, length ~70 km, faulting depth ~24 km, velocity 3.2 km/s, duration 18 s, slip 1.8 m within the asperity, seismic moment 2.0 × 1026 dyne*cm. The two largest imminent foreshocks (Mw = 4.1, Mw = 4.8) occurred very close to the mainshock hypocenter. The asperity bounded up‐dip by the foreshocks area and at the north by the foreshocks/swarm area. The accelerated foreshocks very likely promoted slip accumulation contributing to unlocking the asperity and breaking with the mainshock. The rupture initially propagated northwards, but after 6 s stopped at the north bound and turned southwards. Most early aftershocks concentrated in the foreshocks/swarm area. This distribution was controlled not only by stress transfer from the mainshock but also by pre‐existing stress. In the frame of a program for regular monitoring and near real‐time identification of seismicity anomalies, foreshock patterns would be detectable at least three months prior the mainshock, thus demonstrating the significant predictive value of foreshocks. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
Συγγραφείς:
Papadopoulos, G.A.
Agalos, A.
Minadakis, G.
Triantafyllou, I.
Krassakis, P.
Λέξεις-κλειδιά:
Timing circuits, Controlled NOT; Earthquake catalogues; Hellenic subduction zone; Predictive values; Seismic moment; Stress transfer; Teleseismic; Transient intermediate, Earthquakes
