Temporal and Directional Variations in Shallow Seismic Velocities and Vp/Vs Ratio: Insights From a Borehole Array
Description:
Shallow seismic wave velocity variations are finding new applications in environmental seismology, while remaining important in classical and engineering seismology. From monitoring hydrological processes to landslide stability and accurate site characterization for seismic hazard, it is important to understand and prioritize the natural processes and factors that shape these variations. We contribute to this direction by studying the acceleration data of the ARGONET vertical array (Cephalonia Island, Greece). Our dataset covers the period from July 2015 to May 2024 and includes 1347 earthquake records. Both vertical and horizontal accelerograms are analyzed using the method of seismic interferometry by deconvolution to compute P- and S-wave velocities, respectively. Variations of VP and VS are then examined in terms of time and azimuth, both separately and in the form of their ratio, VP/VS. Several possible factors contributing to the observed variations, i.e., soil moisture, ground shaking level and possible nonlinear soil behavior, earthquake magnitude, back-azimuth and distance, and soil anisotropy are examined. To disentangle the coupled signature of these factors, we apply the method of Generalized Additive Models (GAMs), in which the relationships between independent and dependent variables need not be described a priori as linear or nonlinear. This is particularly powerful in the context of complex relationships between predictors and a response variable. For the soil moisture description, we test both in-situ and modified Copernicus Climate Change Service (ERA5-Land) data. GAMs identify which of the considered predictors contribute with statistical significance to the observed velocity variations and quantify the individual contributions, providing a justified hierarchy for future modeling. At the ARGONET site, the most important factors contributing to the seismic wave variations are the seasonal changes in groundwater, expressed in our analysis through soil moisture, and the nonlinear behavior of the soil.
Session: Station Installations and Site Conditions, a Quest for Improved Strong Motion Database - II
Type: Oral
Date: 4/16/2025
Presentation Time: 04:45 PM (local time)
Presenting Author: Zafeiria
Student Presenter: No
Invited Presentation:
Poster Number:
Authors
Zafeiria Roumelioti Presenting Author Corresponding Author zroumelioti@upatras.gr University of Patras |
Fabrice Hollender fabrice.hollender@cea.fr French Alternative Energies and Atomic Energy Commission, DIMP, DCET, SESN/University of Grenoble Alpes, Université Savoie Mont Blanc, National Center for Scientific Research, French National Research Institute for Sustainable Development, University Gustave Eiffel, Institute of Earth Sciences |
Ioannis Grendas grendasioannis@gmail.com University of Patras |
Nikolaos Theodoulidis ntheo@itsak.gr University of Patras |
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Temporal and Directional Variations in Shallow Seismic Velocities and Vp/Vs Ratio: Insights From a Borehole Array
Session
Station Installations and Site Conditions, a Quest for Improved Strong Motion Database