A model for the Hellenic subduction zone in the area of Crete based on seismological investigations

Abstract

The island of Crete represents a horst structure located in the central forearc of the retreating Hellenic subduction zone. The structure and dynamics of the plate boundary in the area of Crete are investigated by receiver function, surface wave and microseismicity using temporary seismic networks. Here the results are summarized and implications for geodynamic models are discussed. The oceanic Moho of the subducted African plate is situated at a depth of about 50–60 km beneath Crete. The continental crust of the overriding Aegean lithosphere is about 35 km thick in eastern and central Crete, and typical crustal velocities are observed down to the upper surface of the downgoing slab beneath western Crete. A negative phase at about 4 s in receiver functions occurring in stripes parallel to the trend of the island points to low-velocity slices within the Aegean lithosphere. Interplate seismicity is spread out about 100 km updip from the southern coastline of Crete. To the south of western Crete, this seismically active zone corresponds to the inferred rupture plane of the magnitude 8 earthquake of ad 365. In contrast, interplate motion appears to be largely aseismic beneath the island. The coastline of Crete mimics the shape of a microseismically quiet realm in the Aegean lithosphere at 20–40 km depth, suggesting a relation between active processes at this depth range and uplift. The peculiar properties of the lithosphere and the plate interface beneath Crete are tentatively attributed to extrusion of material from a subduction channel, driving differential uplift of the island by several kilometres since about 4 Ma.

Focal mechanism and depth of the 1956 Amorgos twin earthquakes from waveform matching of analogue seismograms

“…Nevertheless, amplitude ratios of body and surface waves from the second event suggest a source at intermediate-depths of at least 100 km. This depth range is in agreement with the observed depths of the WBZ of the subducting Hellenic slab beneath the HVA (Knapmeyer, 1999;Papazachos et al, 2000;Meier et al, 2007;Brüstle, 2012). The proximity in time and space of the two events suggests a triggering of the second, potentially deep event by the shallow first one.…”

“…In both spectra, body waves can be well recognized beyond 0.05 Hz, while, similar to the 2002 Milos event, surface wave signals are very weak in comparison. Based on the very weak surface wave amplitudes in the MFT of the GTT record (compared to the Milos event), we suggest that the second Amorgos event was even deeper than the 2002 Milos event, probably located in the WadatiBenioff Zone of the subducting Hellenic slab, which is located at 120-160 km depth beneath the Santorini-Amorgos graben (Knapmeyer, 1999;Papazachos et al, 2000;Meier et al, 2007;Brüstle, 2012). This hypothesis is corroborated by a HASH focal mechanism analysis (Hardebeck and Shearer, 2002), as already described for the first event, based on 16 first-motion polarities taken from the ISS bulletin (Villaseñor et al, 1997).…”

“…Focal mechanisms of these earthquakes also tend to show NE-SW striking normal faulting mechanisms implying a strong connection to the Kameni-Coloumbo fracture, the southern extension of the western Santorini-Amorgos fault zone. Intermediate-depth seismicity is observed at 120-160 km depth indicating the Wadati-Benioff Zone (WBZ) of the subducting Hellenic slab (Knapmeyer, 1999;Papazachos et al, 2000;Meier et al, 2007;Brüstle, 2012).…”

Receiver function images of the Hellenic subduction zone and comparison to microseismicity

“…Seismicity of the western Hellenic subduction zone (lat < 25 • , profiles 1-4 in Fig. 1) was taken from the relocated EHB-ISC catalogue 1960-2007. Seismicity of the eastern Hellenic subduction zone (lat > 25 • , profiles 4-8 in Fig.…”

“…In the regions of transtensional 138 F. Sodoudi et al: Receiver function images of the Hellenic subduction zone structures in the forearc that have been identified as nearly vertical margins of forearc slivers the seismicity extends down to the subduction interface (Meier et al, 2007;Becker et al, 2009;Brüstle et al, 2014). The seismicity of the plate contact is only incompletely recorded due to the limited station coverage by permanent and temporary networks.…”