The Lefkada, Ionian Sea (Greece), shock (Mw 6.2) of 14 August 2003: Evidence for the characteristic earthquake from seismicity and ground failures

摘要

The earthquake (M w 6.2, Ms 6.4) of 14 August 2003 which occurred in the Lefkada segment of the Cephalonia Transform Fault, Ionian Sea (Greece), was associated with dextral strike-slip faulting striking NNE-SSW. Reevaluation of instrumental and documentary sources show that the 1914, 1948 and 2003 earthquakes ruptured the same fault segment and that all had similar size, which implies that this segment produces characteristic earthquakes. This is verified by the magnitude-frequency diagram which for the instrumental period of 1911-2003 exhibits a relatively narrow range of magnitudes near the maximum (～Ms 6.4), deviation from the log linear relationship and a gap in the moderate-magnitude range. Field observations indicate that the 2003 earthquake and past strong shocks caused on Lefkada island impressively similar ground failures at exactly the same sites: extensive landslides and soil liquefaction, which signifies comparable strong motion features as an additional evidence of the characteristic earthquake. However, while the maximum seismic intensity for the 1914 and 1948 strong shocks is estimated as Imax = IX - X (MM scale), the impact of the 2003 shock was less severe (Imax = VIII) possibly due to building strengthening after 1948.