| 摘要(英) |
From the earthquake catalog of CWBSN, we infer that there exists a low seismicity zone beneath Central Range, around 23.5°N. However, the lateral variation of tectonic beneath Taiwan is very large. To know more about the seismic activity in this area, we use 7 high-resolution seismographs in this study to monitor the distribution of seismicity here. The study area is set in the southern part of Central Range, 120.65°E-121.55°E, 23.0°N-23.9°N. On the condition that unknowing the real velocity of seismic wave in the crust part, there must be some errors during locating an earthquake. For the first part in this study, we use the seismograms of artificial sources(TAIGER) and applying them into three kinds of velocity model, 1-dimension velocity model from CWB(CWB1D), Taiwan 3-dimension velocity model(Wu3D09) from Wu et al.(2007) and Hsieh(2009) 3-dimension velocity model transferred from density model(Hsieh3D07). To improve the accuracy of locating earthquake, we compare the results of three kinds of model and finally choose the CWB1D and Hsieh3D07 model as our velocity model while we’re locating earthquakes. And the other part in this study, we use a broadband seismograph, build by Institute of Earth Scienceof Sinica in 2008 in Haulien(Chiahsin佳心) and the other 6 stations, build by CWB, around Jiashin station, to improve the resolution of recorder(24-bit). To re-find earthquakes during July, 2010, we totally pick 354 earthquakes up, which are not recorded by CWB. In the condition that while an earthquake is recorded by at least 4 stations or there are more than 6 phases, and the ERZ and ERH are less than 5 km, we pick the earthquake up as our new earthquake catalog. From the result of 1-dimension velocity model, most of earthquakes center on Lidau(利稻), Fuli(富里) stations and northern part of Longitudinal Valley. Comparing the distribution of earthquakes during the same time from records of CWB, the pattern is similar. But in this study, it shows that the seismicity in north part of Yuli(玉里) station is more higher and as a strip-shaped like. In the other way, using the new earthquake catalog, comparing the results of 1-dimension and 3-dimension velocity models, it shows that there are similar to each other. But the misfit of 3-dimension velocity model in every aspect is much smaller and has a systematic offset. On the other hand, using the data from Jiashin station is more effective in locating earthquakes for quality and quantity aspects. If we remove the data of Jiashin station, we only have 161 earthquakes, less than half of original earthquakes; besides, in this study, we have 32 complete P-wave and S-wave phases, only detected by Jiashin station. From geometry of stations, these earthquakes may come from the Central Range. Furthermore, discussion with prior researchers, Wang (2009) indicated that the aseismic zone in Central Range belongs to high attenuation zone by using 3-dimension Q-value model. This study shows that this area should have earthquakes. In addition, earthquakes around Lidau station are just located on the area of magnetic anomaly (Yen et al., 2009). Previous research also showed that there had outcrop of igneous rock in Southern Cross-Island Highway. It means that beneath the surface, it may have a high-temperature zone. Depths of earthquakes in this area usually around in 5-20 km, infer that in this area, the occurrence of earthquakes may have related with the high-temperature activities.
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