Crustal deformation associated with east Mediterranean strike–slip earthquakes: The 8 June 2008 Movri (NW Peloponnese), Greece, earthquake (M w6.4)

Abstract

The 2008 mainshock ( M w = 6.4) was the first modern, strong strike–slip earthquake in the Greek mainland. The fault strikes NE–SW, dips ∼ 85°NW while the motion was right-lateral with small reverse component. Historical seismicity showed no evidence that the fault ruptured in the last 300 years. For rectangular planar fault we estimated fault dimensions from aftershock locations. Dimensions are consistent with that a buried fault was activated, lateral expansion occurred only along length and the rupture stopped at depth ∼ 20 km implying that more rupture along length was favoured. We concluded that no major asperities remained unbroken and that the aftershock activity was dominated rather by creeping mechanism than by the presence of locked patches. For M o = 4.56 × 10 25 dyn cm we calculated average slip of 76 cm and stress drop Δσ ∼ 13 bars. This Δσ is high for Greek strike–slip earthquakes, due rather to increased rigidity because of the relatively long recurrence ( Τ > 300 years) of strong earthquakes in the fault, than to high slip. Values of Δσ and Τ indicated that the fault is neither a typical strong nor a typical weak fault. Dislocation modeling of a buried fault showed uplift of ∼ 8.0 cm in Kato Achaia ( Δ ∼ 20 km) at the hanging wall of the reverse fault component. DInSAR analysis detected co-seismic motion only in Kato Achaia where interferogram fringes pattern showed vertical displacement from 3.0 to 6.0 cm. From field-surveys we estimated maximum intensity of VIII in Kato Achaia. The most important liquefaction spots were also observed there. These observations are attributable neither to surface fault-breaks nor to site effects but possibly to high ground acceleration due to the co-seismic uplift. The causal association between displacement and earthquake damage in the hanging wall described for dip–slip faults in Taiwan, Greece and elsewhere, becomes possible also for strike–slip faults with dip–slip component, as the 2008 earthquake.