Abstract

We investigate the interaction between transform faults and normal faults in western Greece based on seismological analysis and static stress transfer calculations associated with the 8 June 2008 Mw 6.4 Achaia earthquake. We present a relocated earthquake catalog for the period between June 2008 and January 2010, when two normal‐faulting events on 18 (Mw 5.3) and 22 (Mw 5.2) January 2010 occurred at Efpalio (western Corinth gulf). They were located approximately 70 km northeast from the buried right‐lateral fault, identified as the causative structure of the Achaia earthquake. The first Efpalio event ruptured a mapped normal fault that trends east‐northeast–west‐southwest, dipping 55°–60° to the south. We estimate ∼2‐fold seismicity rate changes in the western Corinth gulf region for the interseismic period (June 2008–January 2010), and we find that inside this interval, the monthly event rate remained increased at a 2σ significance level. We calculate a Coulomb stress increase (0.1–0.6 bar) in the Efpalio region using optimally oriented for failure planes, and an ∼0.11  bar Coulomb stress increase at the hypocenters of the January 2010 events when incorporating geologically defined receiver planes. We conclude that the positive static stress changes following the Achaia event promoted the observed spatiotemporal clustering in the Corinth gulf for this specific period. We identify fault unclamping due to normal stress reduction as the physical mechanism in this case. The high seismic‐hazard character of the target region (forumla) in the National Building Code emphasizes the importance of time‐dependent earthquake probabilities and stress‐mediated fault interaction studies.

Online Material: Tables of relocated seismicity and station corrections.

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