HR: 0800h
AN: S41A-0934    [Abstracts]
TI: Determination of principal orientations of in-situ stress from anelastic strain recovery measurements of drilling cores close to a fault zone in TCDP Hole-A
AU: * Lin, W
EM: lin@jamstec.go.jp
AF: Program for deep sea research, Institute for research on earth evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Yeh, E
EM: yeh@jamstec.go.jp
AF: Program for deep sea research, Institute for research on earth evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Ito, H
EM: hisao.itou@aist.go.jp
AF: Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Hung, J
EM: jhung@earth.ncu.edu.tw
AF: Dept. of Earth Sciences, National Central University, Jhongda-Road 300, Chung-Li, 320 Taiwan
AU: Song, S
EM: srsong@ntu.edu.tw
AF: Dept. Geosciences, National Taiwan University,, P.O. Box 13-318, Taipei, 106
AB: The state of stress provides insights into understanding the mechanisms of generation and propagation of Chichi earthquake, the anelastic strain recovery (ASR) measurements, therefore, were carried out on the cores taken from the depths close to a fault zone in the Hole-A of Taiwan Chelungpu-fault Drilling Project (TCDP). Four fault zones were encountered between 1100m and 1300m of depth during drilling. Beneath the shallowest fault zone at the depth of 1111m, two cores, which are located at about 1m and 11m away from the gouge in the fault zone respectively, were used to measure the anelastic strain recovery after in-situ stress release by the drilling. The cores were oriented according to the relation between their bedding planes and sedimentary structure of the region. The anelastic strain recovery of the cores was measured in nine directions in which only six directions are independent. For all the directions of both the samples, the expansional anelastic strains were obtained. Their magnitude of the strains in various directions continuously measured for one or two weeks was of the order of 100_~10-6. In additional, the curves of the relation between the strain and elapsed time from beginning of the measurements were very smooth and stable. By using these strain data, a three-dimensional analysis of the principal orientations of in-situ stresses was conducted. The preliminary results showed that the orientations of the major and intermediate stresses exhibited significant local variation in the two depths. The orientations of the minor principal stress at the two depths, however, were roughly the same for each other and approximately equal to west-east orientation with a small plunge. That is, this orientation of the minor principal stress approximately coincides with orientation of the slip displacement of Chelungpu-fault during the Chichi earthquake. Based on some assumptions, the magnitudes of the three principal stresses can be estimated when logging data of rock density has been obtained. Therefore, the shear and normal stress components on the fault plane encountered at 1111m will be estimated.
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2004 AGU Fall Meeting