Shallow Seismic Reflection Exploration in PuliBasin

Ching-Chia Huang

Abstract

The Taiwan island is located in the convergent zone between Eurasian continental plate and Philippine sea plate. Through the plate converge and orogeny, there are a lot of mountains spread on the island. The main mountain chains are CentralRange and HsuehshanRange. The main topography is compressional terrain, but there are some NNE-SSW intermountain basins at the southern Hsuehshan range. Why some subsidence basins appeared at the compression zone? This is a confused question. There are some researches before attempt to interpret the cause of the development of the basin group, but lacking of geophysical evidence, no final conclusion about the structure and the develop process in Puli basin was made.

In this study, we use high-resolution shallow seismic reflection to explore Puli basin, we want to realize the form of the Tertiary basement and the Quaternary formation.

Based on the research conclusion, we can get some summary here: (1).The deepest basement in Puli basin isn’t exceed 600M, and is deeper in western side, the basin sediment layers is 100m depth gravel and deeper sand and mud layer. The shallow gavel layer is deeper in eastern basin. (2).The velocity of P wave in Pili basin is 2200m/s, S wave is 950m/s. The velocity of P wave in basement is 4300m/s, S wave is 2000m/s. Because of the gravel, the velocity of S wave is quick, it means the ground roll is quick, to make some persecution in field work. (3).The basement is Paileng Formation, upper part is thick quartzitic sandstone, the lower part is thick, hard shale. The structure of basement is 2 anticline and 1 syncline, the wavelength is about 4 KM, the wave height is about 1 KM. (4).The basin layer is not horizontal, and is getting tilt deeper, it means the compression is continued between the sedimentary process. The upper gravel layer is near to horizontal, it means the layer was sedimented by river and the structure exercise was getting slow. (5) There are no apparent fault be discovered in Puli basin. (6). The development result of Puli basin is down warping in early period, and the late period is by river erosion.

 

Reference

陳炳誠(2002) 埔里與魚池盆地之沉積與新構造研究。台灣大學碩士論文。

(Abstract) (Full text)

Biq, C. C. (1989) The Yushan-Hsuehshan Megashear zone in Taiwan. Pro. Geol. Soc. China, Vol.32, NO.1 ,7-20

(Abstract) (Full text)

Chen, W. S., Huang, B. S., Chen, Y. G., Lee, Y. H., Yang, C. N., Lo, C. H., Chang, H. C., Sung, Q. C.,Huang,N. W., Lin, C. C. Sung, S. H., Lee, K. J.(2001)1999 Chi-Chi Earthquake:A Case Study on the Role of Thrust-Ramp Structures for Generating Earthquakes. Bulletin of the Seismological Society of America, NO.91,5,pp. 986-994.

(Abstract) (Full text)