HR: 0800h
AN: T11D-1302    [Abstracts]
TI: Seismogenic Structures in Hualien Region, eastern Taiwan
AU: * Kuochen, H
EM: kuochen@scman.cwb.gov.tw
AF: Seismological Observation Center of the Central Weather Bureau, 64,Kung Yuan Road, Taipei, Taiwan 100, Taipei, 110 Taiwan
AU: Wu, Y
EM: drymwu@ntu.edu.tw
AF: National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, Taiwan 106, Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, Taiwan 106, Taipei, 106 Taiwan
AU: Chen, R
AF: Seismological Observation Center of the Central Weather Bureau, 64,Kung Yuan Road, Taipei, Taiwan 100, Taipei, 110 Taiwan
AU: Kuo, Y
AF: National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, Taiwan 106, Taipei, 106 Taiwan
AB: Due to extremely high seismicity and abundant tectonic-influenced geomorphic features, eastern Taiwan has long been known as a tectonically active region. The geological model of an on-going arc-continent collision was successfully proposed to explain the arrangement of the tectonic entities and their interaction. The convergent situation between Eurasia plate and Philippine Sea plate is believed still being existing because of no geomorphic evidence directly related to significant subsidence of the backbone mountain range. However, in the north of the Coastal Range, the Philippine Sea plate is moving northerly downward by the subduction mechanism. Accordingly the fault systems on-land and offshore should be significantly different. With an attempt to answer the puzzle mentioned above we therefore analyze the seismogenic structures in northern part of eastern Taiwan. We adopt the double difference (hypoDD) method to relocate earthquakes, apply the GOCAD (Geologic Computer Aided Design) to visually image the 3D subsurface structures, and determine the rupture plane by the Finite Dimension Source Model (FDSM) from first motion focal mechanisms. Selected earthquakes are (1) located within region between 121.2$\sim$$122\deg$E and 23.5$\sim$$24.5\deg$ N; (2) M$_{ L }$$\geq$3; (3) and showing clearly P or S arrived time at least 6 recorded stations. Additionally, we determine the M $_{ L }$ $\geq$4 focal mechanisms by using the first P wave polarities to examine the reliability of rupture planes determined above. A few of seismogenic structures are clearly identified in this study. Looking at the E-W profile, a major reverse fault dipping $60\deg$ to the east is found in depth of 20-40 km beneath the Coastal Range, which is probably the subsurface image of the plate boundary. On the other hand, within the Central Range several N-S oriented high-angle normal faults are found near the surface in the western part of the study area. The second one from the west reflects the subsurface extension of Lishan fault. In the eastern margin of the Central Range seismic clusters in depth of 10-20 km show high-angle reverse faults. Such a situation of compression down beneath but extension above may suggest a flower structure of the back-bone range. To the Hualien coast and offshore area no more mountains exist but we still found a west-dipping thrust in shallow depth, indicating the existence of the shortening. Further north, a complex seismic cluster is dominated by strike-slip and tensional earthquakes, but no fault plane can be recognized by spatial distribution.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 7200 SEISMOLOGY
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting