GPS OBSERVATIONS OF POSTSEISMIC CRUSTAL MOVEMENTS IN THE FOCAL REGIONOF THE 1995 HYOGO-KEN-NANBU EARTHQUAKE - STATIC AND REAL-TIME KINEMATIC GPS OBSERVATIONS

Post-seismic deformations in the focal region of the 1995 Hyogo-ken Na nbu earthquake (M=7.2), in southwest Japan, which occurred on January 17 (JST), were observed with GPS observations. We deployed more than 3 0 GPS stations in and around the area of aftershock activity within se veral days after the occurrence of the earthquake. First the data were stored and manually collected at the observation sites, but by the mi ddle of February the data at most of sites were started to be telemete red through public phone lines to data centers. GPS observations conti nued until the end of March, except for 4 sites left active for monito ring long-term deformations. We used two types of GPS observations, us ual static and real-time kinematic GPS observations. Static day-by-day analyses, which are based on 24-h data sampled every 30 s, show the d eformation associated with post-seismic readjustment with a relaxation time of about 70 days and with an amplitude of 1-2 cm in the area clo se to the epicenter. Also, rapid movements were observed just after th e occurrence of the earthquake. However, since our analyses are only p reliminary, further analyses are needed to clarify these observations and to investigate models of post-seismic deformations. Real-time kine matic GPS observations, which is a new type of GPS observations, were made every is from February 9 to March 22 for detecting possible rapid relative movements between two sites across the surface fault trace o n Awaji Island and across the other fault, the Arima-Takatsuki Tectoni c Fault on the Kobe side. Present real-time kinematic GPS observations show scatters with the amplitude of 0.5-3.0 cm depending on component s and baseline lengths. Any motions with amplitudes larger than these noise levels could not be detected during the observation period.