胡植慶2006-07-252018-06-282006-07-252018-06-282005http://ntur.lib.ntu.edu.tw//handle/246246/11861GPS measurements with three campaigns in southwestern Taiwan have been carried out by the Central Geologic Survey since 1996 for four years. The Pingtung-Kaohsiung network, which consists of 48 stations, was established to investigate crustal deformation and land subsidence. These GPS surveys mapped the complete velocity field of the Pingtung area in southwestern Taiwan relative to the Paisha station (S01R) of the Penghu islands (located in the Taiwan Strait), a recognizably stable continent shelf. GPS displacement velocities display the trends of variation in the investigated area. The horizontal station velocities varied from 32 mm/yr to 54 mm/yr in azimuths ranging from 247.2 o to 272.6 o with respect to the permanent station S01R. The horizontal station velocities decrease westwards and increase somewhat southwards. In terms of horizontal velocity vector trends, there is a contrast in kinematics in the study area. In the central and western part of the study area, GPS stations move generally toward the west, whereas in the Kaohsiung-Pingtung coastal area, the displacement vectors demonstrate a clear counter-clockwise deviation toward SW. The southern part of coastal area its offshore area show remarkable extension rates of 0.6-2.0 µstrain/year in an azimuth 015°-020°. This significant southward increasing of extensional strain rates is attributed to the lateral extrusion of blocks bounded by major discontinuities in the study area. For the vertical movement, the station velocities are from ~13 mm/yr to -25 mm/yr. There are 20 stations with measured velocities pointing to subsidence in the southern part of the Pingtung plain. The significant subsidence rates from ~ 11 mm/yr to 25 mm/yr have been observed. Our results clearly demonstrate the existence of transtensional deformation which increases southward in the along-strike direction. They are consistent with the Holocene subsidence rate pattern in this region. The long-term subsidence rate is about 4 mm/yr near the coast of the southeastern part of the Pingtung plain. These data are highly consistent with the depositional isopach of fine-grained sediments in the subsidence area. The comparison with Holocene subsidence and isopach of fine-grained sediments suggest that about 75% of the present-day subsidence may result from decreasing groundwater level induced by over-pumping, adding much to the natural risk resulting from tectonic subsidence. We attribute this regional subsidence to be caused by an appreciable drop in groundwater level as revealed by rapid subsidence in the coastal area of the Pingtung plain, as well as the transtentional deformation associated with tectonic extrusion.application/pdf998486 bytesapplication/pdfzh-TW國立臺灣大學地質科學系暨研究所reporthttp://ntur.lib.ntu.edu.tw/bitstream/246246/11861/1/932116M002008.pdf