Abstract. We used the earthquake catalogue of INGV extending from 1 January 2006 to 30 June 2009 to detect significant changes before and after the 6 April 2009 L'Aquila mainshock (M w =6.3) in the seismicity rate, r (events/day), and in b-value. The statistical z-test and Utsu-test were applied to identify significant changes. From the beginning of 2006 up to the end of October 2008 the activity was relatively stable and remained in the state of background seismicity (r=1.14, b=1.09). From 28 October 2008 up to 26 March 2009, r increased significantly to 2.52 indicating weak foreshock sequence; the b-value did not changed significantly. The weak foreshock sequence was spatially distributed within the entire seismogenic area. In the last 10 days before the mainshock, strong foreshock signal became evident in space (dense epicenter concentration in the hanging-wall of the Paganica fault), in time (drastic increase of r to 21.70 events/day) and in size (b-value dropped significantly to 0.68). The significantly high seismicity rate and the low b-value in the entire foreshock sequence make a substantial difference from the background seismicity. Also, the b-value of the strong foreshock stage (last 10 days before mainshock) was significantly lower than that in the aftershock sequence. Our results indicate the important value of the foreshock sequences for the prediction of the mainshock.

No abstract

Abstract. Data on tsunami phenomena occurring in the East Hellenic Arc and Trench system (HA-T) from antiquity up to the present have been updated, critically evaluated and compiled in the standard GITEC format developed in the last decade for the New European Tsunami Catalogue. New field observations are presented for the tsunamis of 9 February 1948 and 24 March 2002. From the 18 tsunamis reported eight are rather well-documented while another nine remain doubtful. The mean recurrence of strong tsunamis is likely equal to about 142 years. Most of the tsunamis documented are caused by strong earthquakes occurring in the area offshore Rhodes to the east or northeast of the island. However, there are large earthquakes near Rhodes that do not cause tsunamis, like the 1926 and 1957 ones, which is of particular importance for the tsunami hazard assessment.

The earthquake (Mw 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 I max = IX − X (MM scale), the impact of the 2003 shock was less severe (I max = VIII) possibly due to building strengthening after 1948.

No abstract