Regional Phases Attenuation in Caucasus

Abstract:

The Caucasus, including the Greater and Lesser Caucasus, the Eastern Anatolian plateau to the east, is formed by the collision of Arabian and Eurasian plates in the late Cenozoic, where the major shortening mechanisms remain poorly understood. Here we are using high-frequency regional phase (Lg and Sn) attenuation models to provide good constraints on the origin of the seismic anomalies in this part of the orogenic belt. With the newest data from the Caucasus Seismic Network (CNET) as well as a number of permanent national network stations, we have updated our Lg and Sn Q models in Caucasus, we are able to obtain relatively good resolution up to 1.5˚1.5˚. In general, extremely low Lg Q0 anomalies (under 100) are observed in the western Greater Caucasus, Transcaucasus, eastern Lesser Caucasus, and part of the south Caspian basin. Relatively low Lg Q0 anomalies (200-300) are observed in the Kura basin, central Lesser Caucasus, Eastern Anatolian plateau, and northern Iranian plateau. High Lg Q0 anomalies (above 400) are observed in the eastern Greater Caucasus, eastern edge of the Kura Bain and the Rioni Basin. For Sn attenuation, we observe very different patterns of Sn Q0 in the western and eastern Greater Caucasus that the western Greater Caucasus is characterized with an extremely low Q0 (<100) while the eastern Greater Caucasus is characterized with a relatively high Q0 (>400). This is consistent with a possibly subducting slab underlying the eastern Greater Caucasus but not the western portion.

In addition, to better quantify the stability and reliability of high-frequency regional phases attenuation models in the study region, synthetic waveform modeling using SW4 and SPECFEM will be applied in order to test how some possible factors would affect the regional phase propagation, including source depth, source epicentral distance, and azimuthal tolerance.