HR: 1330h
AN: T12C-0478    [PDF]
TI: Feasibility Study on Earthquake Precursor Using GPS Data in Taiwan
AU: * Hou, C
EM: hcs@linx.moeacgs.gov.tw
AF: Central Geological Survey, MOEA, No. 2, Lane 109, Hua-Hsin St., Chung-Ho, Taipei, 235 Taiwan
AU: * Hou, C
EM: hcs@linx.moeacgs.gov.tw
AF: Inst. of Geosciences, NTU, No. 1, Sec. 4th, Roosevelt Rd., Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: Inst. of Geosciences, NTU, No. 1, Sec. 4th, Roosevelt Rd., Taipei, 106 Taiwan
AU: Hu, J
EM: jchu@ntu.edu.tw
AF: Inst. of Geosciences, NTU, No. 1, Sec. 4th, Roosevelt Rd., Taipei, 106 Taiwan
AU: Lin, C
EM: lincw@linx.moeacgs.gov.tw
AF: Central Geological Survey, MOEA, No. 2, Lane 109, Hua-Hsin St., Chung-Ho, Taipei, 235 Taiwan
AU: Yu, S
EM: yusb@earth.sinica.edu.tw
AF: Inst. of Earth Sciences, Academia Sinica, P.O. Box 1-55, Taipei, 115 Taiwan
AU: Chen, C
EM: hcs@linx.moeacgs.gov.tw
AF: Central Geological Survey, MOEA, No. 2, Lane 109, Hua-Hsin St., Chung-Ho, Taipei, 235 Taiwan
AU: Wang, J
EM: hcs@linx.moeacgs.gov.tw
AF: Central Geological Survey, MOEA, No. 2, Lane 109, Hua-Hsin St., Chung-Ho, Taipei, 235 Taiwan
AB: Taiwan mountain belt is located at the junction point between Eurasian continental and Philippine sea plates, where an arc-continent collision has been occurred since late Miocene and still on-going. It is unequivocally an earthquake condensed area. Fortunately, most of the earthquakes happen in offshore area and eastern Taiwan along the plate boundaries. Earthquake occurs on land of western Taiwan is seldom but always causes big loss if it strikes the high population district, such as that 1999 Chi-Chi earthquake (Mw7.6). Therefore, the precursor study is urgently needed in such a high earthquake risky area.\\ Among the potential earthquake precursors, GPS has been recently noticed by its improved precision and automation. This study analyzed the datasets of the campaign mode network as well as one station of continuous mode measured in the duration covering the Chi-chi earthquake. We assumed the Penghu islands are relatively stable to fold-and thrust belt of Taiwan, thus all the presented vectors are calculated against the station (continuous mode) set at Paisha of Penghu. On the vector amount, the crustal moving rates are higher in the hanging-wall of Chelungpu-Tachienshan fault ($>$10 mm/yr) than in the footwall ($<$ 10 mm/yr), indicating the stresses are cumulating interseismically. By comparison of the corresponding vectors measured in August of 1997 to 1998 and 1998 to 1999, the moving directions clockwise changed from NW to somewhat due north. This probably represents a stress drop, related to coming large earthquake. If this is a common case, condensed occupations of campaign mode also can serve as an earthquake precursor.\\ On the other hand, we also analyzed the dataset from a continuous mode station (S103) located very close to the southern ending of 1999 surface rupture. Converted vectors consistently show a large annual rate with a direction toward NW during 1995 to 1997. We further found out that its N-S component has no seasonal variation, while the E-W component is obvious (i.e., 8 mm) only in first half of one year and relatively stable in the second half. Until 1998 the E-W shortening started decreasing since the spring and turned to extension (i.e., 6 mm in total) after the summer, which is entirely different from the former annual pattern. We suppose this change is probably a link to the stress drop occurring immediately before earthquake. This finding confirms the GPS monitoring can indeed forecast the earthquake ahead in a few months.
DE: 1206 Crustal movements--interplate (8155)
DE: 7221 Paleoseismology
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting