The 2001 Skyros, Northern Aegean, Greece, earthquake sequence: off ‐ fault aftershocks, tectonic implications, and seismicity triggering

Abstract

The Mw = 6.4 July 26, 2001 Skyros (North Aegean, Greece) earthquake struck the submarine western end of Northern Aegean Sea causing damage in the nearby Skyros Island. It occurred on a left‐lateral NW‐SE trending strike slip fault, oriented transverse to the dominant dextral strike‐slip faults that are present in the area, appearing to mark the boundary between them and the E‐W trending normal faults of the Greek mainland. Foreshock activity started 5 days before the mainshock, and intense aftershock activity followed on the main rupture plane and off fault. The seismogenic structure consists of three clusters with different orientation, independent from the known normal and dextral strike‐slip faults. Theoretical static stress changes from the main shock suggests off‐fault aftershock triggering, providing a tool for assessing the seismic hazard ensuing from strong aftershocks far from the main rupture.

Properties of the 2003 Lefkada, Ionian Islands, Greece, Earthquake Seismic Sequence and Seismicity Triggering

“…where Ds is the shear stress change (computed in the slip direction), Dr is the fault-normal stress change (positive for extension), and lЈ is the friction apparent coefficient that is taken equal 0.6 in the calculations, a value suggested as appropriate for aftershock areas (Harris, 1998;Karakostas et al, 2003). Higher values could be used as well, since the pore pressure is lowered after the mainshock occurrence, in accordance with laboratory experiments for dry rock samples (Byerlee, 1978).…”

Static stress changes due to the 1998 and 2004 Krn Mountain (Slovenia) earthquakes and implications for future seismicity

“…The positive correlation between aftershocks and positive stress lobes was also noted by Toda et al, (1998) who studied stress change patterns following the Kobe, M w =6.9 earthquake and by Steacy et al (2005) who studied four, recent earthquake sequences in Southern California (Landers, Loma Prieta, Hector Mine and Northridge; all events with M w >6.5). Furthermore, a similar distribution was observed during the 2005 eastern-Aegean sequence (Benetatos et al, 2006; three events with M w <6.0) and by Karakostas et al (2003) and Ganas et al (2005) during the 2001 Skyros earthquake sequence (M w =6.4) where Coulomb stress resolved along optimal planes could explain the majority of the off-fault aftershocks. Recently, Chi and Hauksson (2006) showed that static stress increase due to a M w =5.0 earthquake could explain triggered perpendicular seismicity at both ends of a strike-slip rupture.…”

Active Seismotectonic Structures in the Area of Chios Island, North Aegean Sea, Revealed From Microseismicity and Fault Plane Solutions

“…6) and in accordance with the 2001, M5.6 event (strike=244 o , dip=79 o , rake=-164 o ). The coexistence of left- lateral and right-lateral strike-slip faulting or possibly conjugate faulting has also been observed in the western part of the Aegean Sea, where such activation was observed during the 2001 Skyros Island sequence (Karakostas et al, 2003).…”