Lateral variations of shallow shear-velocity structure in southwestern Taiwan inferred from short-period Rayleigh waves
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2003
Received: 16 October 2002
Accepted: 2 July 2003
Published: 20 June 2014
Short-period fundamental-mode Rayleigh waves with periods of 1.1∼5.5 sec were used to investigate the lateral variations of shallow-depth shear-wave velocity structure up to a depth of 8 km under southwestern Taiwan. Through a priori regionalization, the region was divided into three subregions from the west to the east, and then the regionalized group velocity for each subregion was determined by a standard least-squares technique. By the structure inversion, the study region had obviously lateral velocity variations, which systemically increased from the west region to the east one. On the whole, the shear-wave velocity in the Western Foothills was higher than that in the Western Coastal Plain. Additionally, the three subregions all had a shear-wave velocity of less than 3 km/sec with the lowest one in the Western Coastal Plain near the coast, related to the thick sediments. These results were rather consistent with the geological features. For depths larger than 4 km, the velocity-gradient varying with depth in the Western Foothills was lower than that in the Western Coastal Plain. This is likely to interpret the reason that the seismic waves cannot be easily trapped within the Western Foothills; thus the short-period surface waves are poorly developed in that region.