Work

Shallow characteristics of Chenghai Fault Zone, Yunnan, China, from ambient noise tomography and horizontal-to-vertical spectral ratio with two dense linear arrays

Year: 2024

Type: article

Abstract: High-resolution imaging of the shallow structure of a fault zone contributes to the understanding of the regional earthquake hazard and tectonic evolution. The Chenghai Fault (CHF) is located in the eastern margin of the collision zone between the Indian and Eurasia plates, which has accumulated significant shear strain and has hosted several strong earthquakes, but our understanding of its shallow structure remains limited. Therefore, we deployed two dense linear arrays across the Qina and Pianjiao segments of the CHF from October 24 to November 29, 2020. The shallow structure is imaged using ambient noise tomography (ANT), and distinct low-velocity zones (LVZs) are identified beneath the Qina and Pianjiao segments, with widths of ~2.0 km and ~3.3 km and depths of ~0.7 km and ~0.9 km, respectively. These LVZs exhibit a shear wave velocity contrast of 25%–50% relative to the surrounding regions. We also use the HVSR to verify our velocity model, and the geometry and the thickness of the LVZs match well with the interface from the HVSR analysis. The distribution of the high- and low-velocity features is consistent with the regional geological features. The fault damage zone is usually on the order of ~100 m, which is smaller than our result (width of 2–3 km). We interpret the LVZs as sedimentary basins controlled by long-term fault movement and evolution processes rather than fault damage zones. Moreover, the LVZs exhibit notable variations along the strike of the CHF, indicating that the CHF is the factor controlling the development and evolution of the sedimentary basin in this region. The high-resolution shallow velocity structure provides a foundation for understanding the regional ground motion and how the faults affect the regional tectonic evolution.

Source: Tectonophysics

DOI: 10.1016/j.tecto.2024.230351