Definition of Seismogenic Faults by Combining Seismological, Geological and Geophysical Data: Case Studies From the Aegean Sea Area

Geological and geophysical data are often combined with seismological observations to define faults that are related to past, as well as recent catastrophic earthquakes. Such a combination of information from different disciplines is rather required in areas such as the Aegean, where the sparseness of permanent seismological networks on one hand, and the high seismotectonic complexity on the other hand, pose constraints on the efficient definition of seismogenic sources by using seismological methods alone. The 1999 Athens earthquake forms a characteristic example, where combination of seismological, geological and interferometric data was required to accurately locate the seismogenic fault. Proposed hypocenter locations of this earthquake differ as much as 16 km in the horizontal direction and 22 km in depth. The different sets of hypocenter parameters were tested through forward calculations of the surface displacement field, taking into account the distribution of slip during this earthquake, and the resulting fields were compared to interferometric and geological data to determine the best source model. Another example of the effectiveness of the combined geological, geophysical and seismological data sets is the recent determination of the western continuation of the Ganos Fault (Turkey) that ruptured in 1912, within the Gulf of Saros, in northeastern Aegean Sea. Until recently, geological observations supported the theory that the continuation of the Ganos Fault in the Gulf of Saros coincides with the fault along the northern coasts of the Gelibolu peninsula. Nevertheless, the combination of geological information with recent geophysical and seismological data tends to cancel this theory and rather supports that the western continuation of the Ganos fault is located close to the northern border of the Saros depression. These combined studies introduce new data for future seismic hazard studies in the broader area