STRAIN ACCUMULATION IN SOUTHWESTERN TAIWAN

The 1990-1997 annually surveyed GPS data from 36 stations and continuo us data from 3 permanent stations in southwestern Taiwan are utilized to study the spatial and temporal variations of crustal strain in the area. Moderate to remarkable contraction rates of 0.48-2.01 mu strain/ yr in 91 degrees-135 degrees are observed in the vicinity of the Chuko u fault (CKF), The contraction rates decrease toward either the east o r the west. Along the surface trace of the CKF, the strain rates of th e northern segment are approximately at the same level, while that for the central and southern segments clearly increase toward the south. The temporal variations of crustal strain near the CKF are quite unifo rm during the period from 1990 to 1997, Analyzing the repeated GPS dat a of a dense profile across the central segment of the CKF from 1993 t o 1997, it is found that the E-W shortening is distributed at several places and is not solely due to slip along the CKF, The east velocity components relative to Penghu increase dramatically from 2.6 mm/yr nea r the western coast to 39.9 mm/yr in the foothill region to the east o f the CKF, These results indicate that crustal strain is accumulating rapidly and that there is a very high possibility of a forthcoming maj or earthquake in the Chianan area. The extremely high strain rates in the southern segment of the CKF may be caused by the aseismic slip on the fault, as the seismic activity here is insignificant.