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Evaluation of Regional High-Frequency Path Attenuation in Central Mexico Subjected to Subduction Earthquakes and the Potential Impacts on Hazard

Description: 

Attenuation relations play an important role in seismic hazard analysis. In 2020 as part of Next Generation of Attenuation Equation for Subduction Earthquakes (NGA-Sub), global and regional ground motion models have been developed. In this study we evaluated NGA-Sub relation for Central America and Mexico (CAM) in wealth of five decades of Mexican strong-motions database (Instituto de Ingenieria, UNAM). Our initial evaluation of the high frequency ground motions of few of the past subduction-interface earthquakes against the published GMPEs suggested possible systematic bias in the median GMPEs for simulating the expected PGA and Sa0.3 ground motions of subduction zones on stiff sites in Mexico. To further study the issue, we selected strong motion time-history recorded at rock stations for some of damaging historical subduction earthquakes since 1980 to present. Typical misfit analysis was used to compare the recorded ground-motion on sites with reported stiff site conditions with the NGA-Sub for CAM median predicted relations. To avoid the impacts of source effects and possible nonlinear high frequency site effects, the study was limited to the stations at large source-to-site distances. The results of the misfit analysis indicate systematic under estimation of PGA and Sa0.3s both across Central Mexico and along coastal stations compared to the recent GMPEs. The results indicate an even larger bias for the Hill Zone stations within the Mexico City region compared to rock/stiff soil stations across inland and coastal areas, corroborating studies suggesting special high frequency GM amplification within Hill zones due to impedance contrast of low-velocity volcanic rocks overlying higher velocity limestones.

We will present the details of the misfit analysis and our findings on the scale of the bias. We also will present the impact of the GMPE bias in high frequency on regional hazard and risk assessment for low-rise structures in the Mexico City.

Session: Advances in Probabilistic Seismic Hazard Analysis and Applications [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Christine J. Ruhl

Student Presenter: No

Invited Presentation: No

Authors