Routine Regional Moment Tensor Inversion for Earthquakes in the Greek Region: The National Observatory of Athens (NOA) Database (2001-2006)

Abstract

The routine use of regional broadband data for the determination of moment tensors of even very small events ( Mw ∼ 3.5) has considerably enhanced our understanding of tectonic processes in many active regions worldwide ( e.g. , Kao and Jian 2001; Braunmiller et al. 2002; Kubo et al. 2002; Pondrelli et al. 2002; Clinton et al. 2006; Risteau 2008). This development can be attributed to a number of reasons, such as the ability to generate accurate synthetic seismograms for a given velocity model and an increase in the amount and quality of data at regional distances. An additional reason may also be the variety of available methods for regional moment tensor inversion that utilize different parts of the recorded waveform, like surface waves (Thio and Kanamori 1995), body and surface waves (Zhao and Helmberger 1993), or just the long-period part of the signal (Ritsema and Lay 1995). Greece has high seismicity, and large events in the past have caused significant damage and casualties (for an overview see Papazachos and Papazachou 1997). Thus, a systematic study of source properties can help seismic hazard mitigation efforts and offer insights into the seismogenic patterns of the Greek region. Most available source mechanisms of previous events in Greece were derived either from P -wave polarities (Papazachos et al. 1983, 1988; Papadopoulos et al. 1986) or from the inversion of teleseismic waveforms recorded by the Global Seismic Network (Lyon-Caen et al. 1988; Hatzfeld et al. 1996; Bernard et al. 1997; Kiratzi and Louvari 2003; Benetatos et al. 2004). However, the former approach depends heavily on station coverage and the reliability of the first-motion readings, while the latter one can be used only for moderate to large events ( Mw > 5.0). Since 1997 the National …