利用臨時地震網探討中央山脈東南段地震特性

台灣位於菲律賓海板塊與歐亞板塊的聚合邊界，碰撞造山形成現今的中央山脈，同時伴隨著許多地震。從中央氣象局地震觀測網地震目錄中，得知在中央山脈內，有一地震活動較低的地區稱為無震區 (Aseimic zone)，位於東經121∘至121.5∘、北緯23∘至23.7∘。此區域地震站數量不似西部地震網密集，為進一步了解此區地震活動，本研究新增多個高解析度的臨時地震站，並聯合中央氣象局地震觀測站及中研院地球所寬頻地震站，進行地震及長微震定位。本研究目視搜尋氣象局地震目錄未定位之地震，分別對氣象局ㄧ維速度模型(CWB1D)與中央山脈南段ㄧ維速度模型(Chen12)，進行定位誤差討論，結果選定Chen12模型並進行定位。經由選定之誤差條件篩選後，最後挑選出581個氣象局地震目錄未定位之地震。與氣象局地震目錄型態大至相符，其中央山脈地震深度較淺為25公里以上，而花東縱谷與海岸山脈地震深度較深為20~50公里。中央山脈地震群集主要分布在：雙龍、玉山、利稻站附近。在本研究區域南邊，大水窟站與大分站周圍確實存在許多小規模地震。然而北邊23.6 ﾟN仍呈現無震，因為此位置未設置地震站，故無法釐清是否為無法偵測小規模地震或溫度影響所致。除了地震，本研究同時也觀測到許多非火山長微震 (non-volcanic tremor, NVT)。經由波包交相關(WECC)方法定位，其初步位置位於無震區北邊121ﾟE, 23.6ﾟN，與前人中央山脈南段非火山長微震震源區於120.8 ﾟE，23.1 ﾟN更為北邊0.5度。綜合地震分布、非火山長微震分布、衰減值分布、磁力異常分布等結果，顯示研究區域北邊與南邊的岩性有所不同。本研究認為研究區域北邊岩石強度弱化而地震活動度極低，其高溫環境有利於長微震發生。而研究區域南邊確實有淺層微震活動，可能與熱構造活動或流體活動有關。

關鍵字

無震帶；非火山長微震

並列摘要

Taiwan is located in the boundary between the Philippine Sea and Eurasian plates. The Taiwan orogen is created by the collision between the continental shelf of the Eurasian plate and the oceanic crust of the Philippine sea plate. Currently, we have deployed 4 temporary seismic network in southeastern Central Range and combined with the earthquake data of the Central Weather Bureau of Taiwan (CWB) and Broadband Array in Taiwan for Seismology (BATS) to study the seismicity in this area. Totally, there were 581 earthquake with good quality of location from June to November, 2013 which are not recorded by CWB. Comparing the distribution of earthquakes during the same time from records of CWB, the pattern is similar. In the past study, there is an aseismic zone in our study area. However, we found some small magnitude earthquakes near DFN and DSK station in the southern of study area. Meaning the increase of station can help us to get small earthquake to complete the catalog of seismicity even though in aseismic zone. Besides, we also observed non-volcanic tremors (NVT). By using waveform envelope cross correlation method to locate 4 ambient tremors. The preliminary results is located at northern aseismic zone with the depth from 25 to 40 km. the source are more north of 0.5 degrees that compared with previous research in the southern Central Range. Furthermore, discussion with prior researchers, Wang et al. (2010) indicated that aseismic zone belongs to high attenuation zone and Hsieh et al. (2014) indicated that aseismic zone have high geothermal gradient. Concluded above, the rock strength weakening in the northern study area, while the southern part although sensitive to high temperatures but still have shallow micro-seismicity that may cause by an active thermal structure or shallow fluid-related activities.

並列關鍵字

Aseismic zone ； non-volcanic tremor ； NVT

參考文獻

陳奕敦. (2012). 台灣南部中央山脈之突發性孤立地震群特性探討

Chuang, R. Y., Johnson, K. M., Wu, Y., Ching, K., & Kuo, L. (2013). A midcrustal ramp‐fault structure beneath the Taiwan tectonic wedge illuminated by the 2013 Nantou earthquake series. Geophysical Research Letters, 40(19), 5080-5084.

Hsieh, H., Chen, C., Lin, P., & Yen, H. (2014). Curie point depth from spectral analysis of magnetic data in Taiwan. Journal of Asian Earth Sciences, 90, 26-33.

Ide, S. (2012). Variety and spatial heterogeneity of tectonic tremor worldwide. Journal of Geophysical Research: Solid Earth (1978–2012), 117(B3)

Kao, H., Shan, S., Dragert, H., Rogers, G., Cassidy, J. F., & Ramachandran, K. (2005). A wide depth distribution of seismic tremors along the northern Cascadia margin. Nature, 436(7052), 841-844.

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利用臨時地震網探討中央山脈東南段地震特性

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