SURFACE WAVE PHASE VELOCITY DISTRIBUTION
Supervisor: Kazunori YOSHIZAWA
The crustal and upper mantle structure beneath Turkey is investgated by using phase velocity of fundamental-mode Rayleigh waves working with a two-station method. We used vertical component seismograms of 72 broad-band seismic stations in Turkey and surrounding areas from 172 teleseismic events from April 2005 to June 2007. The average dispersion curve of the entire region of Turkey is estimated from path-average dispersion curves in a period range from 20 to 160 s. The average phase velocity of Turkey is found to be about 3-9 % slower than the global average even if we consdier a crustal correction for Turkey. We generate path coverage maps as a function of frequency indicating the path-specific phase velocity with colors, and perform two kinds of analysis using the paths with high accuracy to clarify the regional variations of phase velocity in Turkey. Both the phase velocity coverage maps and two studies on localized phase velocity distributions indicate that the fastest phase velocities are observed in the north-western part of Turkey (i.e., the Marmara Region) and the phase speed becomes slow in the eastern part of Turkey. We may explain the observed fast phase velocities in the northwestern part of Turkey by the cooling of the upper mantle, which can affect the immersion of oceanic lithosphere of the Black Sea beneath southward margin of the Marmara region and the slow phase velocities in the eastern Turkey by the presence of conjugate strike slip fault system (EAFZ) and Bitlis thrust zone as well as partially molten litospheric mantle which can be inferred from the wide spread of young volcanism (< 2Ma). The previous geological (i.e. heat flow, volcanism and tectonics) and seismological (i.e. Pn-wave velocity distribution, Sn-wave attenuation) studies strongly support our results.
|Citation: ||Bulletin of IISEE, 42, 49-54.|