← Back to Sessions

Application of Bayesian SPAC to Estimate Vs30 and Classify Soils in Ponce, Puerto Rico

Description: 

The city of Ponce, one of Puerto Rico’s largest urban centers, is characterized by significant variations in topography and soil conditions, which result in differences in seismic wave amplification across the area. To address these variations, seismic design standards such as ASCE 7-22 recommend adjusting seismic design spectra based on local soil characteristics. Accurate estimation of the average shear-wave velocity in the upper 30 meters of soil (Vs30) is crucial for ensuring resilient infrastructure and promoting sustainable urban development. In line with the United Nations’ Sustainable Development Goal No. 9, which advocates for resilient infrastructure, the Spatial Autocorrelation (SPAC) method provides a non-invasive, Cost-effective way to estimate Vs30, making it ideal for densely populated cities like Ponce.

This study applied the SPAC method at 10 locations across Ponce, utilizing three concentric circular arrays (or three common-base nested triangle arrays), with the largest circle having a radius of at least 30 meters. Data were recorded over a minimum of four days to capture dynamic variations in ground behavior at different times of day and week. Hierarchical Transdimensional Bayesian Inversion was then employed to analyze the coherence curves derived from the SPAC data, enabling the calculation of shear-wave velocity profiles and Vs30 values at each site. These Vs30 values were subsequently used to classify the soils according to the National Earthquake Hazards Reduction Program (NEHRP) standards.

The results revealed that most of the studied sites in Ponce are classified as soil type C or worse, indicating soils with limited energy dissipation capacity that are likely to amplify seismic waves. Interestingly, the coherency curves at bedrock sites displayed unexpected behavior, that’s why the model fits were more accurate for sites with soil layers than for bedrock, where the SPAC-derived shear-wave velocity profiles closely matched the observed data. These findings contribute to a more precise characterization of Vs30, A key parameter for estimating seismic loads buildings must withstand.

Session: Why Ignore the Structure? Soil-structure Interaction and Site Response at Local and Regional Scales [Poster]

Type: Poster

Date: 4/17/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Melissa

Student Presenter: Yes

Invited Presentation: 

Poster Number: 9

Authors