HR: 12:05h
AN: S42A-08    [Abstracts]
TI: Three Dimensional P-Wave Velocity Structure Beneath Eastern Turkey by Local Earthquake Tomography (LET) Method
AU: * Teoman, U M
EM: ugurt@boun.edu.tr
AF: Bogazici University, Kandilli Observatory and Earthquake Research Institute, Cengelkoy, Istanbul, 34684 Turkey
AU: Turkelli, N
EM: turkelli@boun.edu.tr
AF: Bogazici University, Kandilli Observatory and Earthquake Research Institute, Cengelkoy, Istanbul, 34684 Turkey
AU: Gok, R
EM: gok1@llnl.gov
AF: Lawrence Livermore National Laboratory , 7000 East Avenue, Livermore, CA 94550 United States
AB: Recently, crustal structure and the tectonic evolution of Eastern Turkey region was extensively studied in the context of Eastern Turkey Seismic Experiment (ETSE) from late 1999 to August 2001. Collision of the Arabian and Eurasian plates has been occurring along East Anatolian Fault Zone (EAFZ) and the Bitlis Suture, which made Eastern Turkey an ideal platform for scientific research. High quality local earthquake data from the ETSE seismic network were used in order to determine the 3-D P-wave velocity structure of upper crust for Eastern Turkey. Within the 32-station network, 524 well locatable earthquakes with azimuthal gaps < 200° and number of P-wave observations > 8 (corresponding to 6842 P-phase readings) were selected from the initial data set and simultaneously inverted. 1-D reference velocity model was derived by an iterative 1-D velocity inversion including the updated hypocenters and the station delays. The following 3-D tomographic inversion was iteratively performed by SIMULPS14 algorithm in a ``damped least-squares'' sense using the appropriate ray tracing technique, model parametrization and control parameters. As far as resolution is concerned, S waves were not included in this study due to strong attenuation, insufficient number of S phase readings and higher picking errors with respect to P phases. Several tests with the synthetic data were conducted to assess the solution quality, suggesting that the velocity structure is well resolved down to ~17km. Overall,resulting 3-D P-wave velocity model led to a more reliable hypocenter determination indicated by reduced event scattering and a significant reduction of %50 both in variance and residual (rms) values.With the influence of improved velocity model, average location errors did not exceed ~1.5km in horizontal and ~4km in vertical directions. Tomographic images revealed the presence of lateral velocity variations in Eastern Turkey. Existence of relatively low velocity zones (5.6 < Vp < 6.0 km/sec) along most of the vertical profiles possibly indicates the influence of major tectonic structures such as North Anatolian Fault Zone (NAFZ), East Anatolian Fault Zone (EAFZ) and the Bitlis thrust belt correlated with the seismicity. Low velocity anomalies extend deeper along EAFZ down to ~15km compared to a depth of ~10km along NAFZ. Arabian plate is generally marked by relatively higher velocities (Vp > 6.2 km/sec) in 10-15 km depth range.
DE: 6982 Tomography and imaging (7270, 8180)
DE: 7200 SEISMOLOGY
DE: 7270 Tomography (6982, 8180)
SC: Seismology [S]
MN: Fall Meeting 2005