Sediment thickness distribution beneath the source and adjacent area of the Jishishan earthquake: A short-period dense array study
Meng Fan-chang, Li Bo*, Sun Hui, Xu Shan-hui, Wang Chang-zai
1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
2. National Field Scientifi c Observation Research Station of Earth Science at Beijing Baijiatuan Beijing 100081, China
3. China University of Geosciences (Beijing), Beijing 100083
4. School of Earth Science and Engineering, Southwest Jiaotong University, Chengdu 610097, China
Abstract：
Reliable thickness of sedimentary layers is essential for seismic hazard assessment in active fault zones,especially in regions prone to strong earthquakes. This study analyzed the seismic ambient noise data recorded by 60 short-period seismic stations deployed at the Jishishan earthquake source and adjacent areas. The base-order resonance frequencies of sedimentary layers beneath the stations were determined using the horizontal-to-vertical spectral ratio method on ambient noise with different frequencies. Then, a resonance–thickness formula was applied to estimate the sedimentary layer thickness at each station. Finally, the entire regional sediment thickness was obtained via interpolation. The thickness of the sedimentary layer beneath each station was estimated using the equation of the relationship between resonance frequency and sedimentary layer thickness, and finally, the distribution of sedimentary layer thickness in the whole region was obtained by interpolation. Results reveal notable spatial variations in sediment thickness in the source and adjacent areas. The shallow sedimentary layer in the source area is relatively thick at approximately 100 m, whereas that in Liugou Village, which is the most severely damaged area, is approximately 150–180 m. In the western region, specifically along the western edge of the Jishishan Mountain rupture and the Pourouliuhe–Cheunhua Nanshan rupture zone, the shallow sedimentary layer is approximately 30–60 m. A comparison between the distribution of seismic secondary hazards and sedimentary layer thickness highlights a strong correlation between these hazards and the amplifi cation eff ects of seismic waves. In regions with thicker sedimentary layers, ground shaking is signifi cantly amplifi ed, resulting in more serious seismic secondary hazards. In addition, the study confi rmed that secondary hazards, such as landslides and liquefaction, were more prevalent in regions with thicker sedimentary layers. These fi ndings provide an important reference for post-earthquake reconstruction, seismic risk assessment, and the development of regional disaster prevention and mitigation strategies.
. Sediment thickness distribution beneath the source and adjacent area of the Jishishan earthquake: A short-period dense array study[J]. APPLIED GEOPHYSICS, 2025, 22(2): 264-278.
2025, Vol. 22 
