HR: 1330h
AN: T12C-0463    [PDF]
TI: Slip-rate Estimation of Active Fault by Luminescence Dating on Deformed River Terraces at Tsaotun, Central Taiwan
AU: * Chen, Y
EM: f90224212@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, P.O. Box 13-318, Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, P.O. Box 13-318, Taipei, 106 Taiwan
AU: Chen, W
EM: wenshan@ms.cc.ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, P.O. Box 13-318, Taipei, 106 Taiwan
AU: Lee, C
EM: ct@gis.geo.ncu.edu.tw
AF: Institude of Applied Geology, National Central University, No. 300, Jungda Rd., Chungli, Taoyuan, 320 Taiwan
AB: This study carried out luminescence ages of the deformed terraces located at Tsaotun in central Taiwan. These terraces are considered as a result of crustal deformation caused by recent activity of the Chelungpu fault, 1999 surface rupture. Since this active fault runs through urban area, it is urgently needed to figure out its neotectonic behavior, including slip-rate and recurrence interval. Based on new ages, we also discuss the terrace correlation and its related structures. The study terraces are all strath terraces with only a few meters of veneered fluvial deposits on top. Due to the strong stream-power, nearly all the outcrops are dominated by fluvial cobbles, which is worst condition to preserve the syndepositional carbonaceous materials. Alternatively, optical stimulated luminescence (OSL) dating uses sandy quartz as the material and even has longer dating upper limit (up to several hundreds of years). Fortunately, sandy layer are found intercalated within the fluvial cobbles in studying terraces. We adopted the Single-Aliquot Regenerative (SAR) dose protocol on large aliquots of 90-150$\mu$m quartz, which were cleaned using HCL, H$_{2}$O$_{2}$ and HF in the usual way. In case of incomplete bleaching during quick deposition, the OSL/TL ratio was adopted to approach the true De. Dosimetry is derived by ICP-MS and XRF analyses. For ascertainment of the initial bleaching of fluvial sediment, the modern samples collected in river bed of Wuhsi were also measured. Based on the results of modern samples, we believe that the residuals are inevitable in younger sediments, especially along the upper stream. On the contrary, the samples older than 10 kyr are little influenced due to the larger age error than the younger ones. The OSL age of the terrace samples in the hanging wall is dated ca. 13 kyr, which has been corrected for poorly-bleaching problem. Comparing to the ages collected down hole in the footwalls, we found out vertical displacements of ca. 67 and 37 m, has been cumulated by the slips of main and back thrust. Thus, the long-term slip rates of the main and back thrust are 3.8-6.5 m/kyr and 2.0-3.8 m/kyr, respectively. If we consider that the 1999 Chi-Chi earthquake is a characteristic event, a recurrence interval of 300-600 years is derived.
DE: 0932 Radioactivity methods
DE: 1035 Geochronology
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting