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A Simple Way of Estimating Site Effect With Respect to a Distant Rock-Reference Site: Application of the Standard Spectra Ratio Technique Based on Coda Waves

Description: 

In recent years, site effect is considered having a major impact on the earthquake ground motion. Site effects can be described by the Site spectral Amplification Factor (SAF) which is directly controlled by surface geological conditions (briefly: hard rock to loose sediments into valleys). Several simple or more sophisticated techniques have been introduced in recent decades, with advantages and disadvantages leading to certain limitations. One of the most commonly applied SAF estimation techniques is the so-called Standard Spectra Ratio (SSR) (Borcherdt, 1970). However, this technique can only be applied if there is a rock reference station close to the studied site. This condition is obviously restrictive for all sites where no reference/rock station is installed nearby. In this study, the SSR technique is studied and examined based on Coda wave recordings, using time segments corresponding to the same travel time, based on more distant reference stations (thus bypassing the criterion of the nearby reference site). It should be noted that this technique, named SSRc (for SSR on coda waves), is simple to implement. It is an alternative to the more complex methods developed previously by Philips and Aki, (1986) and Grendas et al.,(2022a), which also use Coda waves, attempting and partially succeeding in relaxing the criterion of proximity to the reference site. The valid application of this new SSRc technique is supported based on analytical attenuation equations and synthetic parameters, as well as based on actual earthquake data. More specifically the SSRc technique is successfully applied here at several stations in two different seismicity contexts in wester Greece and southeastern France with high seismicity and low-to-moderate, respectively, using relatively distant reference stations (e.g. up to ~100km). The computed average SAF results, as well as their uncertainty, are encouraging compared to corresponding results extracted by alternative methodologies and different dataset, supporting thus further application and investigation of the proposed, and rather simple, SSRc technique.

Session: How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far? - I

Type: Oral

Date: 5/1/2024

Presentation Time: 08:30 AM (local time)

Presenting Author: Ioannis

Student Presenter: No

Invited Presentation: 

Authors