利用位於台灣中央山脈區域之TAIGER炸測計畫資料建立台灣地下三維速度構造

Three Dimensional Velocity Structure Beneath Taiwan by Using the Data Recorded Along the Central Range of Taiwan in the TAIGER Experiment

吳政倫(Cheng-lun Wu)

指導教授 ： 石瑞銓

國立中正大學/理學院/地球與環境科學系應用地球物理與環境科學研究所/碩士(2013年)

摘要

台灣位在歐亞大陸板塊與菲律賓海板塊之間，地下構造相當複雜。雖然過去已有很多對於台灣島地下構造的研究，但仍有些不足。在2008年，為了更加了解台灣的弧陸碰撞系統模式，於台灣進行名為台灣地體動力整合計畫(TAIGER)的炸測計畫。野外施測已成功完成，並且蒐集到廣大的數據資料。在當時，於台灣的中央山脈設置了共108個地震儀，以記錄到能沿著南北方向構造的資料。在本研究中，我們將利用這108測站的資料來得到台灣的地下三維速度構造。震源包括有8個大型的炸藥炸測：北端的N1、N2、N3p、N4以及南端的S1、S2、S3、S4，南北端各自的四個炸點皆沿著東西向排列。為了使震波到時更易於辨識，我們對於原始資料進行濾波與訊號增益控制等處理。得到清晰初達波到時的資料後，再利用由Zelt & Barton (1998)所建立的FAST三維反演程式進行地下速度構造逆推。初始速度模型選擇為由表面速度4.5km/s漸漸加快至80公里深處的8.2km/s。根據結果，我們可以看到在北方的地下速度構造比起南邊要複雜的許多。若利用速度6.2km/s作為一個重要的速度邊界，此速度邊界於南部的深度會較中部與北部深，西側深度也深於東部，整體上，此速度邊界落在深度20~30公里之間。而在更深的區域也可觀察到另外的主要速度邊界7.8km/s的出現，但因為波線的覆蓋程度較少，可以看到的區域也侷限在台灣中部區域，以南北向作比較，北部較淺，南部較深。但在許多的剖面可觀察到在中央山脈之下的速度邊界可深達60km，以整體資料分析，深度範圍約在45~60km之間。

關鍵字

地下深部速度構造

並列摘要

Taiwan is located in a convergent boundary between the Eurasian plate and the Philippines sea plate; the subsurface structure is very complicated. Many studies have been conducted in this area to clarify the detailed subsurface structure of the island; however, more works are still needed. In 2008, an active source experiment named Taiwan Integrated Geodynamic Research (TAIGER) was conducted around Taiwan for better understanding the Taiwan arc-continent collision system. The field experiment was successfully accomplished, and an extensive dataset has been collected. In the meantime, there were 108 seismographs installed in the central mountain range of Taiwan, along the principal tectonic structure of Taiwan in the North-South direction to record the valuable data. In this paper, we will present 3D subsurface velocity structure beneath Taiwan, by using the data recorded from the 108 stations. The seismic sources consist of eight large-scale dynamite shots deployed across the recording line in the West-East direction; four shots (N1, N2, N3p, and N4) in the north and another four shots (S1, S2, S3, and S4) in the south, respectively. We have processed the data with editing, amplitude balancing, and filtering to identify the arrival time of seismic waves. The data were then processed by using the 3D inversion program, FAST, developed by Zelt to construct the subsurface velocity structure. An initial model of velocities 4.5 km/s at the surface down to 8.2 km/s at the depth of 80 km was chosen. From the results, we may see that the subsurface velocity structure in the north is much complicated than that in the south. A major boundary of velocity 6.2 km/s could be observed in the velocity structure, and that boundary is deeper in southern Taiwan than that in the north. The overall depth of boundary is approximately from 20 to 30 km. The other major boundary of velocity 7.8 km/s was also seen, but appeared at certain places, which was probably limited by the density of ray coverage. In this study, better coverage area is mainly located on mid Taiwan. Overall distribution of the boundary is approximately from 45 to 60 km. In coverage area, the boundary of velocity 7.8 km/s is deeper in southern Taiwan than in the northern Taiwan. Also, it can find that has deeper boundary under the central mountain range of Taiwan, which is 60 km.

並列關鍵字

TAIGER ； tomography

參考文獻

Kim, K. H., J. M. Chiu, J. Pujol, K. C. Chen, B. S. Huang, Y. H. Yeh, and P. Shen (2005) , Three-dimensional Vp and Vs structural model associated with the active subduction and collision tectonics in the Taiwan region, Geophys. J. Int., 162, 204– 220.

Kuo-Chen Hao, F- T. Wu, S- W. Roecker (2012), Three-dimensional P velocity structures of the lithosphere beneath Taiwan from the analysis of TAIGER and related seismic data sets JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, B06306.

Wu, F. T., R. J. Rau, and D. Salzberg (1997), Taiwan orogeny: Thin-skinned or lithospheric collision? , Tectonophysics , 274, 191–220.

Wu, Y.-M., C.-H. Chang, L. Zhao, J. B. H. Shyu, Y.-G. Chen, K. Sieh, and J.-P. Avouac (2007), Seismic tomography of Taiwan: Improved constraints from a dense network of strong-motion stations, J. Geophys. Res., 112, B08312.

Vidale, J. E. (1990), Finite-difference calculation of traveltimes in three dimensions, Geophysics, 55, 521 -526,