[S-SS08] Crustal Structure

[SSS08-P08] 3D Upper Crustal Shear-Wave Velocity Model of Eastern Taiwan from Ambient Noise Tomography with Dense Seismic Arrays

*Hao Kuo-Chen¹, Ching-Yu Cheng², Dennis Brown³, I-Chin Yen⁴, Kai-Xun Chen¹, Wei-Fang Sun¹, Zhuo-Kang Guan¹, Shen-Hsiung Liang⁵, Wen-Shan Chen¹, Chu-Wei Ho⁶ (1.National Taiwan University, 2.National Central University, 3.CSIC, 4.YIC Geological Office, 5.Ministry of Economic Affairs, 6.Central Weather Administration)

Keywords:ambient noise tomography, dense seismic array, eastern Taiwan

Eastern Taiwan is recognized as a boundary of arc-continental collision between the Eurasian Plate and the Philippine Sea Plate, resulting in complex tectonic and geological structures. These active structures frequently generate earthquakes and pose significant hazards. Therefore, developing a high-resolution and well-constrained 3D shear-wave velocity model of the upper crust is crucial for understanding the region’s subsurface architecture. In this study, we conducted an ambient noise tomography experiment using 411 seismometers deployed in 5 dense seismic arrays along the Longitudinal Valley and the Coastal Range. The reliable Rayleigh wave phase velocity periods range from 0.6 to 14 seconds, enabling a well-resolved Vs structure from the surface to a depth of around 6 km. The Vs model reveals a prominent NNE-striking variation in Vs that along the trend of tectonic units. Lateral and vertical velocity variations observed in the region align with known geological structures and fault zones, highlighting the heterogeneous lithological compositions. Specifically, the Longitudinal Valley shows low-velocity anomalies at shallow depths, while the Coastal Range exhibits distinct velocity contrasts. The high-resolution model successfully resolves finer-scale structures within the upper 6 km of the crust.