| dc.description.abstract | Taipei city, the capital of Taiwan, is located in the Taipei basin. The thick recent deposits in this ‘soft’ basin have caused significant earthquake damage due to site amplifications, although the earthquakes have mostly occurred outside the basin. The top near-surface layer, called the Sungshan formation, is thought to carry the burden of the site-effects, because of its loose sand and silt content.
Over the past 10 years, the Central Geological Survey has conducted a wide-range of investigations of the Taipei basin by drilling over 30 wells (100-700m). During the same period, we have also scanned the basin area (20x20 km) using over 300 shallow reflection seismic lines. The purpose of this paper is to compile these seismic data, incorporating it with the borehole drilling results, to better describe the Tertiary basement, the Quaternary layers above the basement and their P- and S-wave velocities. It is found that 1) the deepest part of the basin basement is probably at the outlet of the Tanshui river, i.e., at the NW corner of the basin, 2) the Kanchiao fault forms a separation boundary bisecting the basin into a deep NW part and a shallow SE part, 3) the sharp of the basement implies the Sanchiao fault may be long enough to penetrate under the Tatun volcanic region in the north. 4) there are two low-velocity area in the, the NW and SE corner of the basin, 5) the depth of the Sungshan formation from 50 to 120 meter and the S-wave velocity is about 120~350m/sec. The S-wave velocity of the Chingmei formation is 450m, and the S-wave velocity of the basement is 1000m/sec. | en_US |