| Summary: | 碩士 === 國立中央大學 === 地球物理研究所 === 88 === Detecting the Hukou Fault by Shallow Seismic Reflection Method
Liang-An Lin
ABSTRACT
The Hukou fault is located at the northern border of the Hukou terrace. It runs almost in the east-western direction. Physiographically, the fault looks like a scarp along the terrace’s boundary and is generally attributed as an active fault.
The purpose of this study is to detect the Hukou fault and the structures in its vicinity using the shallow seismic reflection method. Several long-range seismic lines (400 m long) are distributed perpendicular to the fault trace with the visible seismic images down to the depth of 700 meters. Besides this, we also used five short-range seismic lines across the Hukou anticline, from the edge of the terrace to Tienzuhu, to investigate the structure of this fault-related anticline. After carefully reserving the characteristics of each reflector, we are able to correlate different layers on different seismic profiles.
On the seismic profiles, we find that all structure layers vary quite smoothly. The layers bend upward, but not broken at the suspected place of the Hokou fault. It seems that the scarp represents a boundary of curved stratum (i.e. part of an anticline), not a presentation of an actual fault. Furthermore, the positions where the structures bend are shifted to the east from the cliff of the terrace by about 50 m. The young Tienzuhu Formation has covered this shifted area. Thus, we tend to propose that a blind thrust fault might hide at the bottom and it makes the ‘fault-bend’ fold structure.
We also found that the Hukou anticline is an asymmetric anticline. It is steeper in the north flank than in the south flank. The axis is extended toward the southeast of Pingchen and becomes closer to the fault with decreasing uplift. One important seismic images are obtained on the plane area where the young lateritic terrace deposits is obviously disturbed by the tectonic stress. Because of this, we intend to propose that the potential risk of the fault activity might not be ignored.
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