GPS観測から求めた東地中海および中東地域の地殻歪

Velocity vectors estimated by GPS observations in the Eastern Mediterranean and Middle East region were used to investigate the crustal strain distribution in this region. Nine years of data from 1988 to 1997, estimated by McCLUSKY et al. (2000) were used to derive principal components of strains. We employed the Least-Squares Prediction (LSP) technique to segregate signals and noise in the data. Estimated signals were used to reconstruct the strains; dilatations, maximum shear strains, and principal axes of strains. Results of crustal strains clearly portray active tectonic strains in the study region. There are large convergent strain rates in the Mediterranean Sea, along the Hellenic Arc and south of it, which are directly related to the subduction of the African plate along this arc. Large extension strain rates with orientations varying between NNE-SSW and N-S are found in northern Aegean Sea and northwestern Anatolia. The southern Aegean Sea is characterized by relatively small strain rates. Convergent strain rate is dominant in the northeastern Africa, but occurs at a relatively low rate. Patterns of strain rates located north and south of the Bitlis suture are quite similar, suggesting that most of the motion of Arabia is being transferred directly to Anatolia. East of the Karliova triple junction (KTJ), the compressional axes of strains show a tendency of being more easterly toward the NNE, resulting in shortening normal to the Caucasus thrust front. There is no indication of active deformation (almost strain-free) along the Cyprean Arc, south of Turkey, and near the Gulf of Iskenderum. Strain rates and level of earthquake occurrence are low in the central part of Anatolia, indicating that internal deformation in this region is very small. The principal axes of GPS strain rates show remarkable agreement with seismic data and fault plane solutions. In general, distinct seismic clusters accompany the areas of high geodetic strain rates, whereas the strain-free regions are nearly aseismic