← Back to Sessions

Noise-Based Estimation of Local Seismic Amplification in an Industrialized Area of the French Rhone Valley

Description: 

Shallow sedimentary layers may be responsible for dramatic ground motion amplification and increase the duration of shaking when an earthquake occurs. These local modifications of ground motion are usually associated with site effects. Often associated with sedimentary basins, site effects are due to the impedance contrast at the interface between soft soil layers filling the basin and the bedrock. For site effects assessment, methods based on ambient noise might be of great interest in low-to-moderate seismicity regions.

In this study we evaluate the applicability of SSRn and SSRh (noise-based and hybrid Standard Spectral Ratio, Perron et al. 2018) to assess site effects in the Tricastin region in the French Rhone Valley. This area is prone to generate complicated site effects associated with the valley's incised geometry and the strong lithological contrast between the sedimentary filling and the bedrock. We recorded ambient noise between February to March 2020 on a 400-sensors array. Previous studies have shown that important source effects might bias the resulting amplification factor of SSRn above 1 Hz. To attenuate these local source effects, we introduced a two-step workflow based on the spectral characteristics of the signal. Our workflow relies on a careful time window discrimination for removing strong transient signals and an automatic data selection through a clustering algorithm. By applying this method, we were able to remove strong anthropic transient signals at some sites and therefore improve the amplification assessment above 1 Hz through SSRn and SSRh. We also show that some sites are biased by permanent sources that remain an issue in quantifying the amplification at larger scale. Finally, we explore new strategies based on interferometric methods to overcome the limitations of these approaches. By involving phase coherence, we expect the correlations to better filter uncoherent local sources and give better estimates of the amplification.

Session: From Sensors and Networks to Site Characterization and Site Response: Coming Full Circle

Type: Oral

Date: 4/18/2023

Presentation Time: 10:15 AM (local time)

Presenting Author: Loïc Gisselbrecht

Student Presenter: Yes

Invited Presentation: 

Authors