HR: 10:20h
AN: T11F-01 INVITED     [PDF]
TI: Surface Deformation and Earthquake Potential of Tainan Tableland, Southwestern Taiwan
AU: * Rau, R
EM: raurj@mail.ncku.edu.tw
AF: Department of Earth Sciences, National Cheng Kung University, Tainan, 701 Taiwan
AU: Ching, K
EM: jing_kuen@sinamail.com
AF: Department of Earth Sciences, National Cheng Kung University, Tainan, 701 Taiwan
AU: Hsieh, T
EM: joshua@sgrc.ncku.edu.tw
AF: SGRC, National Cheng Kung University, Tainan, 701 Taiwan
AU: Yu, C
EM: yujyh@mail.ncku.edu.tw
AF: Department of Surveying Engineering, National Cheng Kung University, Tainan, 701 Taiwan
AU: Hou, C
EM: hcs@linx.moeacgs.gov.tw
AF: Central Geological Survey, MOEA, Taipei, 235 Taiwan
AU: Lee, Y
EM: dljp@linx.moeacgs.gov.tw
AF: Central Geological Survey, MOEA, Taipei, 235 Taiwan
AU: Hu, J
EM: jchu@ccms.ntu.edu.tw
AF: Department of Geological Sciences, National Taiwan University, Taipei, 106 Taiwan
AU: Chan, Y
EM: yuchang@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Taipei, 115 Taiwan
AU: Lee, J
EM: jclee@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Taipei, 115 Taiwan
AU: Hung, J
EM: t260001@cc.ncu.edu.tw
AF: Department of Earth Sciences, National Central University, Chungli, 320 Taiwan
AU: Lin, C
EM: lincw@linx.moeacgs.gov.tw
AF: Central Geological Survey, MOEA, Taipei, 235 Taiwan
AB: During the past 100 years several damaging earthquakes in the foreland of southwestern Taiwan have originated from rupture of blind thrusts that are manifested only by folding on the surface. It is important to identify the location, geometry, and size of the causative blind fault segments in order to estimate the potential for major earthquakes in this region. Geodetic measurements of surface deformation on the folded terrains are used to determine the fault geometry and the slip behavior at depth. We carried out repeated GPS and precise leveling measurements on the Tainan tableland, southwestern Taiwan in order to better understand earthquake potential in this densely populated urban area. Analysis of GPS campaign data set from 1999 to 2003, together with data recorded at eight continuous GPS sites in the surrounding areas, indicate that the Tainan tableland block moves northwest at 12 mm/yr relative to a fixed west coast site. For the domain east of the tableland, site velocities increase to 17 mm/yr with directions E-W relative to the fixed site. To the north and south of the tableland, from west to east, E-W-directed velocities increase gradually from 17 to 40 mm/yr. Comparisons of five precise leveling surveys across Tainan tableland over a period of 2 years indicate a uniform uplift rate of about 11 mm/yr for benchmarks within the 5-km-wide tableland. Elevation changes are virtually undetectable for benchmarks on west of the tableland. East of the tableland, on the contrary, uplift rate changes abruptly from 11 mm/yr to nearly zero near the margin of the tableland across the Houchiali fault. Farther east, benchmark uplift rate increases again from 0 to 12 mm/yr over a distance of 4 km to the eastern end of the leveling profile. By a dislocation model in an elastic half space, the geodetic data indicate that the Tainan tableland deformed as a pop-up structure with a major east-dipping thrust and a west-dipping backthrust. Both thrusts are blind faults. The backthrust (the Hochiali fault) are formed possibly due to a change of dip angle of the major east-dipping fault (the Tainan fault), which likely connects to a sub-horizontal regional detachment farther to the east. From the best-fit model we obtained a rapid slip rate of 23 mm/yr on the $32\deg$ east-dipping Tainan fault and a relatively slow slip rate of 5 mm/yr on the $75\deg$ west-dipping Houchiali fault. Both faults extend from near surface to a depth of 4 km, where the two faults are connected. With empirical relations between rupture area and earthquake magnitude, we estimate a single segment earthquake Mw 5.7 could take place on the Houchiali fault.
DE: 1204 Control surveys
DE: 1208 Crustal movements--intraplate (8110)
DE: 7223 Seismic hazard assessment and prediction
DE: 8102 Continental contractional orogenic belts
SC: Tectonophysics [T]
MN: 2003 Fall Meeting