Repeating earthquakes in western Corinth Gulf (Greece): Implications for aseismic slip near locked faults

Abstract

An extensive search for repeating earthquakes was performed in the western Corinth Gulf by applying waveform cross-correlation on 22 000 earthquakes that occurred in 2008-2014. Event pairs with high correlation coefficient (CC ≥ 0.95) recorded by two or more stations are classified as multiplets of repeating events. The highly similar event pairs have typically interevent distances less than a quarter wavelength (~150 m for a dominant frequency of 10 Hz) and are used to estimate the accuracy of the relocated catalogue. A detailed analysis of the spatio-temporal properties of the repeating sequences revealed two types of repeating events, namely, burst-like and continuous-type repeaters. Burst-like repeaters are widespread in the entire study area, mostly associated with seismic excitations located at depths between 5 and 9 km, triggered either by fluid intrusion or stress transfer. Their duration is short with high values of coefficient of variation in recurrence intervals (COV > 1) and high slip rates. The continuous-type repeaters, which last 1-7 yr, with COV~1 and slip rates almost 0.26 cmyr-1, forma very narrow shallow north-dipping seismic zone at 10 km depth along the Psathopyrgos and Aigion faults. That kind of activity provides strong evidence for aseismic slip in thewestern Corinth Gulf and defines the boundary between brittle and ductile layers in the area.