Fault Zone Drilling in the Backstop to the Mediterranean Ridge Accretionary Complex off Crete, Greece

Abstract

Scientific drilling and the installation of downhole seismic instrumentation to observe seismicity at a low-magnitudea low-magnitudelow-magnitude detection threshold are powerful tools to monitor denselyare powerful tools to monitor densely powerful tools to monitor densely to monitor densely populated areas in Southern Europe, such as the Athens such as the Athens metropolitan region, to minimize societal and environmental to minimize societal and environmental dangers, which millennia ago destroyed entire cultures, two of the seven wonders of the world (Colossus of Rhodes 224 BC, Lighthouse on Pharos 365 AD) and several historical sites in the circum-Mediterranean. The EasternThe Eastern Mediterranean hosts one of the most prominent retreating convergent margins worldwide that was capable of gener-of gener- gener-ating M>8 earthquakes (365 AD, western Crete) anding M>8 earthquakes (365 AD, western Crete) and M>8 earthquakes (365 AD, western Crete) and exhaustive volcanic eruptions (1650 BC, Santorini) in historic times.The Hellenic Subduction Zone (HSZ) in the Eastern Mediterranean Sea represents a mature subduction zone where African crust is thrust (i.e., subducted) beneath Eurasiaandwhereawidebackstopareaofpartlyoldaccreted and whereawidebackstopareaofpartlyoldaccreted a wide backstop area of partly old accreted strata (marine), partly HP/LT rocks (the exhumed island ofthe exhumed island ofexhumed island of Crete as forearc high), an extensional submerged landward forearc (Cretan Sea), and a volcanic arc and backarc basin (Aegean Sea) evolved. The HSZ is an ideal natural laboratory to study collisional processes which are well recorded overrecorded overrecorded over the past ca. 35 million years, including an intermittent stage of micro-continent collisions between about 30 Ma and between about 30 Ma andMa andand 20 Ma, followed by breakoff of the subducting slab, and incipient collision with the passive African margin today (Thomson et al., 1998). The island of Crete represents a horst structure developed within the last 5 million years in the central forearc, and it provides excellent onshore access to and it provides excellent onshore access toit provides excellent onshore access toprovides excellent onshore access to the internal structure of the forearc at various levels (for overall geodynamic situation in map view, see Fig. 1).