[1] We installed 5 broadband and 45 short-period temporary seismic stations, distributed partly as a dense, 100-km-long, N-S linear array and partly as a regional network, throughout the Menderes Massif of western Turkey in order to study crust-upper mantle structure and seismicity. In this study, we have combined teleseismic waveform data from these stations with data from several permanent seismic stations to determine crustal thickness variations in the Aegean region. Receiver function studies at seven broadband stations, using the H-k stacking method, have yielded crustal thicknesses and V p /V s ratios over a broad region of the Aegean. A more detailed crustal image was obtained in the central Menderes Massif, where we applied common conversion point stacking to receiver functions obtained from the N-S linear array. The results show a general trend of westward crustal thinning from 36 km in central Anatolia to 28-30 km in the central Menderes Massif to 25 km beneath the Aegean Sea. The results also indicate that crustal thinning in the Aegean is not uniform in the N-S extensional direction. The crust is thinner in the central Menderes Massif (28-30 km of crustal thicknesses) and the Cycladic Massif (25-26 km) than in surrounding regions where crustal thicknesses are 32-34 km. The longlived elevated Moho under the metamorphic core complexes suggests that the lower crust in the Aegean region is at least 3 times more viscous than that in the Basin and Range Province, where the Moho is much flatter.

S U M M A R YWestern Anatolia is one of the most seismically active continental regions in the world and much of it has been undergoing NS-directed extensional deformation since Early Miocene time. In a cooperative study, seismologists from Saint Louis University, USA and Dokuz Eylül University, Turkey, deployed five broad-band and 45 short-period seismic stations in western Anatolia between 2002 November and 2003 October. The present paper uses data collected by this network and the data from five permanent stations operated by the Kandilli Observatory and Earthquake Research Institute to map the hypocentral distribution of local earthquakes and to determine crustal structure of western Anatolia. We obtained a 1-D P-wave crustal velocity model using a generalized scheme for simultaneously obtaining earthquake locations and a crustal velocity model. Our velocity model is characterized by crustal velocities that are significantly lower than average continental values. The low velocities may be associated with high crustal temperatures, a high degree of fracture, or the presence of fluids at high pore pressure in the crust. We located 725 local earthquakes and classified them in three categories. We found that the level of seismic activity in western Anatolia is higher than previously reported. Station delays resulting from the inversion process correlate with near-surface geology and the thickness of sediments throughout the region. The hypocentral distribution of the events indicates that peak seismicity for the region occurs at depths of about 10 km.

[1] We have relocated 364 earthquakes in western Turkey between 2002 and 2003 using more than 45,000 accurate P and S differential travel-times. We also have determined moment tensors for 71 of these earthquakes using their broadband regional waveforms. After relocation the events are highly concentrated in three clusters and delineate two nearly vertical faults. Their strikes agree with the strike of one of the fault planes of the averaged fault-plane solution of the cluster, which allowed us to pick the true fault plane and the slip direction. We identified a NNW-striking leftlateral strike-slip fault near Buldan that connects the Gediz graben in the north and the eastern end of the Buyuk Menderes graben in the south. The other right-lateral strikeslip fault near Izmir strikes ENE -WSW direction. Our results indicate that part of the N-S extension occurring in western Turkey is accommodated by strike-slip faults and is accompanied by E-W shortening. Citation: Zhu, L., N. Akyol, B. J. Mitchell, and H. Sozbilir (2006), Seismotectonics of western Turkey from high resolution earthquake relocations and moment tensor determinations, Geophys. Res. Lett., 33, L07316,

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Ð We have used micro-earthquake recordings (M 1.8±4.1) of local events in the distance range of 5±60 km in order to quantify the attenuation and site eects in the vicinity of the Bursa city, Marmara region, Turkey. The data set consists of 120 three-component recorded accelograms from 69 earthquakes, recorded at six stations. Each station is deployed on dierent geologic units, such as massive limestone, slope deposit and Quaternary young sediments, in the framework of the Marmara Poly-Project.In this study a nonparametric inversion method was applied to acceleration records from the Bursa region to estimate source, site and path eects using a two-step inversion. At the ®rst step, we determined attenuation functions by analyzing the distance dependence of the spectral amplitudes and retrieved values of Q s f 46:59f 0:67 . At the second step, the corrected S-waves spectral records for the attenuation function, including the geometrical spreading eect, were inverted to separate source and site response for 21 dierent frequencies selected between 0.5 and $25 Hz. The near-surface attenuation, j value, was also estimated by using the model proposed by ANDERSON and HOUGH (1984) at each site. We observed that j 0 is smaller for stations located on rock site (I gdir, SIGD, j 0 $ 0:004) compared to the one that is located on Neogene sediment (C Ë ukurca, SCKR, j 0 $ 0:018).Site ampli®cations from inversion showed that the station located within the Bursa basin, C Ë ukurca (SCKR), is the most important site with about 4.0 ampli®cation value at 1.8 Hz. DemirtasË (SDEM) ampli®es the spectral amplitudes about 3.0 times at 2.0 Hz, SHMK about 3.5 times between 2.5 and 3.5 Hz and SHMT nearly reaching 3.5 times between 1.5 and 4.0 Hz. However, stations located on the UludagAE Mountain Massif (SKAY and SIGD), which correspond to a deep limestone geological unit, have the smallest ampli®cation, that values between 0.6 and 1.4.