For the last 10 years Chinese seismologists have been studying the seismic velocity ratio anomalies before and after a series of strong and moderate earthquakes (Feng, D. et al., 1974; Feng, D., 1975; Feng, D. et al., 1978) Since many seismologists hold different viewpoints on using premonitory seismic velocity variations as earthquake precursors,we must continuously make detailed studies of the different characteristics of the seismic velocity anomalies in different region.
In this paper, we collected data for the V_P/V_S anomalies before and after some earthquakes occurred in Province Gansu and its vicinity with magnitude about 4 and >4 during the period 1970-1983.
We have investigated and discussed some general temporal and spatial characteristics of V_P/V_S anomalies; namely, the time-dependent characteristics of V_P/V_S variations, and the spatial characteristics of regions concerning the future strong or moderate earthquakes.