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Modeling of HVSR for an Inhomogeneous Medium Over a Varying Lateral Interface Using 3D IBEM and the Diffuse Field Concept

Description: 

The single-station microtremor horizontal-to-vertical spectral ratio (HVSR) method is a powerful tool to retrieve the dominant frequency and shear velocity structure of soft soil locations. Its appeal lies on its simplicity: no artificial sources are required, and single-station, three-component observations are sufficient to estimate soil properties, making it a highly cost-effective technique. Numerous studies have explored the interpretation and modeling of HVSR. Assuming that seismic noise behaves as a diffuse field, which implies that microtremors are generated by random sources, accounting for multiple scattering effects and having sundry types of elastic waves. The diffuse field theory establishes a direct relationship between the average energy density and the imaginary part of the Green’s function when the source and receiver coincide. Theory remains valid even for anisotropic and inhomogeneous media.

The Indirect Boundary Element Method (IBEM) is a numerical approach based on integral equations and fundamental solutions. It has been formulated in the frequency domain which makes it inherently well-suited for HVSR modeling. However, its application to heterogeneous media has posed a significant challenge due to the lack of suitable fundamental solutions for such materials. In this work, we present an analytical approximation for the fundamental solution for 3D elastic wave propagation in a vertically inhomogeneous medium with constant velocities gradients and demonstrate its application to HVSR modeling using the Diffuse Field Concept (DFC). This advancement not only extends the applicability of the DFC but also enhances our understanding of wave behavior in complex geological settings and demonstrate IBEM's ability to handle varying lateral interfaces effectively.

Session: Numerical Modeling in Seismology: Theory, Algorithms and Applications - I

Type: Oral

Date: 4/17/2025

Presentation Time: 09:00 AM (local time)

Presenting Author: Oscar Isao

Student Presenter: Yes

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