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 cm yr −1 , form a 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 the western Corinth Gulf and defines the boundary between brittle and ductile layers in the area.

Repeating earthquakes record fault weakening and healing in areas of megathrust postseismic slip

“…REs, earthquakes with nearly identical waveforms, magnitudes, and locations have been previously recognized and studied in the lab oratory and observed in multiple natural fault systems in California (5)(6)(7)(8), Japan (9)(10)(11)(12)(13)(14), Mexico (15), Greece (16), Taiwan (17), and Costa Rica (18). They are thought to represent the repeated rupture of the same fault asperity at a relatively constant recurrence interval (t r ) due to continuous loading by surrounding aseismic slip (19,20).…”

Mapping Intrinsic and Scattering Attenuation in the Southern Aegean Crust Using S Wave Envelope Inversion and Sensitivity Kernels Derived From Perturbation Theory

“…In the Gulf of Corinth, we observe high Q i −1 and high Q sc −1 in all frequency bands. High Q sc −1 regions are closely associated with a shallow (5–15 km) north‐dipping zone of continuous earthquake activity identified by seismicity studies in this area (Mesimeri & Karakostas, 2018 and references therein). This zone forms the root of the shallow faults that have normal and strike‐slip components as imaged in seismic sections (Beckers et al, 2015).…”

Rheological behaviour in continental and oceanic subduction: inferences for the seismotectonics of the Aegean Region

“…In particular, profile G seems to perfectly fit all along the projected seismicity from the NKUA moment tensors catalogue and the relocated seismicity of Kassaras et al (2016). Transect H (Figure 11b) is in a geodynamically more internal position, closer to the volcanic arc and with higher heat flow; it is thus characterized by a thinner brittle layer, which is nicely mimicked by the seismicity distributions of Hatzfeld et al (1995), Ganas et al (2012), Kassaras et al (2016), Mesimeri and Karakostas (2018), and the NKUA moment tensors catalogue. Only a few events occur much deeper than the shallow BDT, between the Corinth Rift and the Argolikos Gulf, and they are possibly related to local increases in pore fluid pressure or very small-scale rheological heterogeneities as previously discussed ( Figure 10).…”