Investigation of Sediment Thickness and Site Effects in the Guye Seismic Source Zone, Tangshan, Using the HVSR Method

Sediment thickness is an important reference for evaluating the site effects of seismic waves and a critical indicator for assessing seismic disaster losses. Based on the Horizontal-to-Vertical Spectral Ratio method (HVSR), this study calculates sediment thickness and evaluates site effects using nearly one year of ambient noise data recorded by a dense seismic array in the Guye seismic source zone. The results show that the sediment thickness in the study area ranges from 0 to 450 m, with a significant difference between the eastern and western parts. The site amplification factor varies from 1.0 to 14.0. The site vulnerability index exhibits a spatial pattern of high values in the west and low values in the east. The western zone with thick sediments has a high risk level of 60–110, indicating a high seismic risk region for building damage. This study further reveals that the 2020 M s 5.1 Guye earthquake occurred in the thin-sediment zone in the northern Tangshan Fault zone. Stress diffused along the fault after the 1976 event and concentrated in the thin-sediment area to drive this earthquake. The pronounced site effects in this region further intensify the ground motion intensity. The synergistic coupling between the strong seismic source input from fault activity and site effects gives rise to anomalous ground motion, thus forming an anomalous seismic damage zone. The results of this study can provide a scientific basis for regional seismic hazard risk assessment, engineering seismic fortification, and earthquake prevention and disaster mitigation.