HUNTING FOR ULTRA-LOW VELOCITY ZONES USING SKS AND SKKS DIFFERENTIAL TRAVEL TIME RESIDUALS

Ultra-low velocity zones (ULVZs) play a key role in the geodynamics of the lowermost mantle. Consequently, mapping the location of these structures are critical to our understanding of mantle processes such as plume formation. Here we use SKS and SKKS waveforms from teleseismic earthquakes southeast of the Phillipines recorded in Turkey between 2005 and 2010 by the Kandili Observatory, the National Seismic Network of Turkey and the Nothern Anatolian Fault Experiment to hunt for the presence of ULVZs. SKS – SKKS differential travel-time residuals were calculated for the available high quality data. Correlation statistics between the measured SKS-SKKS residuals and the observed absolute travel time delay of the individual SKS and SKKS phases for three high quality events were further analyzed to determine the path, SKS or SKKS, contributing to observable residual differential travel-times. This statistical analysis in combination with geographic mapping and interpretation of the observed residual differential travel-times results in three probable ULVZ structures located at 0º – 5º latitude and 135º E - 142º E longitude, 8º N – 13º N latitude and 127.5º E - 132.5º E longitude and 35ºN – 46ºN latitude and 66º E – 76º E. These results are in agreement with other than the previous observations of ULVZs located near the boundary of Large Low Shear Velocity Provinces.