The Greek Database of Seismogenic Sources (GreDaSS): state-of-the-art for northern Greece

Abstract

The Greek Database of Seismogenic Sources (GreDaSS) is a repository of geological, tectonic and active-fault data for the Greek territory and its surroundings. In this report, we present the state-of-the-art of an on-going project devoted to the building of the GreDaSS, which represents the results of decades of investigations by the authors and a myriad of other researchers working on the active tectonics of the broader Aegean Region. The principal aim of this international project is to create a homogeneous framework of all of the data relevant to the seismotectonics, and especially the seismic hazard assessment, of Greece and its surroundings, as well as to provide a common research platform for performing seismic hazard analyses, modeling and scenarios from specific seismogenic structures. In particular, we introduce and synthetically describe the results obtained (and included in the database) to date in the northern sector of continental Greece and the Aegean Sea. As a first step we collected all available (both published and unpublished) historical and instrumental seismicity data relevant to the determining of the causative faults. Following the experience of recent 'surprising' earthquakes (e.g. 1995 Kozani, and Athens), we realized the deficiency of such an approach, and decided to also include in the GreDaSS active faults (i.e. seismogenic sources) recognized on the basis of geological, structural, morphotectonic, paleoseismological and geophysical investigations. A second step is the critical analysis of all of the collected data for the extraction of the necessary seismotectonic information, enabling the recognition of as many seismogenic sources as possible, as well as their characterization and parameterization. The most updated version of the database consists of numerous seismogenic sources that are categorized into three types: composite, individual, and debated. In this report, we describe the major seismotectonic properties of all of the composite seismogenic sources and individual seismogenic sources in northern Greece, which imply the partitioning of the area into five sectors that show similar internal behavior. Northern Greece was chosen as a pilot area because the parameters and accompanied metadata of its seismogenic sources show a high level of confidence and completeness. The amount of information and the degree of uncertainty is different for the three types.

Rheological behaviour in continental and oceanic subduction: inferences for the seismotectonics of the Aegean Region

“…See text for discussion. dipping SW with an average angle of 55° to 60° (Caputo et al, 2012), and it is considered as the source for the 1999 M w = 6.0 Athens earthquake (Papadimitriou et al, 2002;Papadopoulos et al, 2002;Ganas et al, 2004). The BDT in this region is quite shallow, with an average depth of 11-12 km (Figure 12b), consistent with the focal depth, determined at 8 km, and the aftershocks not recorded below 11 km (Voulgaris et al, 2001).…”

“…For the friction coefficient parameter, a reference value of 0.6 has been selected, which is consistent with the classic experiments and review of Byerlee (1968Byerlee ( , 1978, and it lies in the interval (0.5-0.8) of the most common values also proposed by Ranalli (1995). In order to account for a lower coupling along major active faults, we assigned slightly lower values down to 0.5 in correspondence to the main seismogenic sources (from the GreDaSS database; Caputo et al, 2012;Caputo and Pavlides, 2013) crossed by our transects. Such a choice is based on the higher wearing, comminution, abrasion, and mineralogically related weakening that occur on seismic shear zones and faults, as documented by, e.g., Collettini and Holdsworth (2004), Chiaraluce et al (2007), Middleton and Copley (2014).…”

“…However, the onset of the current stress field for the broader Aegean Region can be traced back to Middle Pleistocene times (Mercier, 1976;Le Pichon and Angelier, 1979;Mercier et al, 1989;Caputo and Pavlides, 1993) and it is characterized by an almost N-S minimum stress (σ 3 ) direction, with a slight rotation of the trajectories towards the NNW-SSE in northwestern Greece. The current N-S crustal stretching, which is greatest in the Corinth Rift (15 mm/a; Briole et al, 2000;Avallone et al, 2004;Caputo et al, 2012), is likely due to an accelerated slab roll-back along the Hellenic Arc (e.g., Faccenna et al, 2014).…”

“…In this section we exploit the results obtained from the rheological modelling for seismotectonics purposes and for possibly contributing to the improvement of the seismic hazard assessment of the broader Aegean Region. In particular, the obtained depth of the BDT is used as a constraint to determine, independently of other sources of data, the geometrical (width and secondarily length) characteristics of the seismogenic sources (Caputo et al, 2012) crossed by the transects. In other words, the rheological modelling and the reconstructed 'shallow' BDT depth allow to define the seismogenic layer thickness and therefore also to constrain the maximum credible magnitude.…”

“…Although more complex strength profiles with more than one BDT are possible, for the aims of the present paper devoted to crustal seismotectonic applications, we focus on the shallowest BDT, which usually occurs between 10 and 20 km (Sibson, 1982;Scholz, 1988), though locally deeper (35-40 km). On the other hand, the occurrence of a second deeper brittle layer is unlikely to produce a (Caputo et al, 2012) are represented as well as the traces of the transects generated by interpolation of densely spaced 1D rheological profiles. CTF indicates the Cephalonia Transform Fault.…”