Near surface wave velocity structure in Chinese capital  region based on borehole seismic records

Firstly we collected P and S waveform data from 102 earthquakes with Mge;3.0 for the period 2003 to 2008 observed at 58 borehole stations obtained from the Capital Circle Digital Seismic Telemetry Network catalog. After identifying direct wave and surface reflection wave, we found their delay time varied little despite distinct epicentral distances and azimuths. Based on Snell's law, we developed travel time lags to compute average wave velocity in about 300 meters of soil layer above each station. Our results show that near-surface P-and S-wave average velocity in Chinese capital region ranges from 1.6 to 2.0 km/s and 0.34 to 0.48 km/s respectively,vP/vS is about 4.0mdash;5.3. Furthermore, no obvious lateral variation of P-wave velocity structure or vP/vS is observed by comparing results of 11 borehole stations with the same depth of 247 m. The clear seismic phases for both P-and S-wave suggest no significant velocity discontinuity in the soil layer. The results are useful in both the simulation of strong ground motion and the calculation of detailed velocity structure in the crust or upper mantle, as well as some areas of earthquake engineering.