Microseismic activity and seismotectonics of Heraklion Area (central Crete Island, Greece)

Abstract

A seismological network of 10 portable analogue stations was installed in the area of Heraklion (central Crete) from September to December 1995. During this period, more than 1000 events were recorded by at least 4 stations with magnitudes ranging from 0.5 to 4.6 and depths up to 70 km. Analysis of 336 well located events revealed high seismic activity. In the onshore area seismicity is shallow (<20 km) and concentrated along the eastern margin of the Heraklion Basin and in the Messara graben to the south. Seismicity decreases rapidly from east to west, with practically no events located along the western boundary of Heraklion Basin. Epicenter distribution indicates that microseismicity is closely associated to the tectonics of the region. Significant seismic activity was also observed in the southern offshore area, restricted north of the Hellenic Trench and related to the subduction process. The determination of different types of focal mechanisms in the area indicates that the investigated region is characterized by complex tectonics related to the southward subduction of the African plate and the northward extension of the Aegean lithosphere.

Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network

“…14a). This activity close to the southern coast of Crete was also identified in earlier microseismicity studies of the region (Delibasis et al, 1999;Meier et al, 2004b;Becker et al, 2006) using land-based seismic networks. Combining our findings with the ISC catalogue (Engdahl et al, 1998) which also lists seismic events with intermediate magnitudes in that area we conclude that the Ptolemy structure constitutes a continuously seismically active feature in the Aegean crust.…”

“…15). The northern part of the interplate seismicity was also observed by earlier land-based temporary networks (Delibasis et al, 1999;Meier et al, 2004a) while these studies were not able to detect its southern termination due to the lack of offshore stations. This interplate seismicity is rather evenly distributed and no locked zones indicating possible areas of stress accumulation were detected.…”

“…In 1988 a study of microseismic activity covering the whole southern Aegean Sea recorded only sparse microseismic activity onshore Crete while most activity occurred south of Crete between the Pliny trench and the coast (Hatzfeld et al, 1993). A study conducted in 1995 in central Crete (Delibasis et al, 1999), however, found significant microseismic activity in the Messara graben, the Heraklion Basin and in the southern offshore region at the Ptolemy trench. This latter activity was also observed during a 2000/2001 field campaign aimed at studying the microseismic activity in central Crete (Meier et al, 2004a).…”

“…Delibasis et al, 1999;Becker, 2000;Meier et al, 2004b;Meier et al 2007) are available in addition to global catalogues covering the second half of the 20th century (e.g. Engdahl et al, 1998).…”

Structure of the Hellenic Subduction Zone from Gravity Gradient Functions and Seismology

“…According to the results of the studies conducted by MEIER et al (2004a); DELIBASIS et al (1999), the region lying in the south of Cretan Island has great seismological activity at depths of 20-40 km.…”