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Seismic Site Response in the Binchuan Basin, Yunnan, China Inferred From Records at a Dense Linear Array

Session: How Well Can We Assess Site Effects So Far? [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 03:45 PM Pacific

Description: 

The earthquake ground motions atop basins could be significantly amplified and prolonged by the uppermost unconsolidated sediments and the deeper impedance contrasts. In this study, ground motion records of both local and teleseismic earthquakes from a temporary dense linear array are used to investigate the site response parameters in and near the Binchuan Basin in northwestern Yunnan, China. We first calculate the spectrum of all events at each individual station. Then we derive the spectral ratios between the spectrum from one single station and the average from 10 stations outside the lowest velocity zone. The results show that (1) the amplification effects are most prominent in the middle of the array, where a prominent low-velocity zone was discovered from ambient noise tomography, and (2) the spectral ratios show peaks at the frequencies from 0.4 Hz to 0.6 Hz for local earthquakes and slightly higher frequencies for teleseismic earthquakes with smaller incident angles. We interpret that the amplification at lower frequencies (< 1.0 Hz) results from the basin resonance. Therefore, deeper structures such as the sediments/bedrock impedance contrasts should also be taken into consideration while characterizing the site response. The amplification at higher frequencies (1 Hz to 5 Hz) is attributed to the loose sediments in the uppermost tens of meters, which could be further verified by ground motion modeling based on the shallow subsurface Vs structures. We demonstrate that the dense array recordings could be used to quantify the site responses with higher spatial resolution and more appropriate parameters.

Presenting Author: Junhao Song

Student Presenter: Yes

Authors