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WITHDRAWN Upper Plate Control on Earthquake Stress Drop: Comparison Between High and Low Ground Velocity Zones in Costa Rica

Description: 

WITHDRAWN Despite its small area, Costa Rica’s tectonics is highly complex and geophysically diverse. Upper plate dynamics (crustal deformation and seismicity) is strongly influenced by the interaction of four tectonic plates: The Cocos plate, the Caribbean plate, the Panama microplate and the Nazca Plate, modulating the generation of M+7 megathrusts every 40 to 50 years, the abundant microseismicity, intermediate magnitude earthquakes, Slow Slip Events, Low Frequency Earthquakes (LFEs) and Landslides. The notorious presence of sedimentary basins, a large shear zone located in the Central Valley and active volcanic chains, lead the region to a wide range of peak ground velocity (PGV) measures following the occurrence of earthquakes at short and large distances. For example, we analysed the records from 25 teleseismic events with magnitudes between 7.0 and 7.5, using a very dense broadband seismic network operated by the Volcanological and Seismological Observatory of Costa Rica (OVSICORI), we observed that the Talamanca Mountain Range, predominantly composed of well-consolidated Miocene volcanic rocks, represents an area with low PGV. In contrast, the Tilaran Range, mainly consisting of poorly consolidated Pleistocene volcanic rocks, exhibits anomalously high PGV values. Both the Talamanca Mountain Range and the Tilaran Range show clustered and well-aligned seismicity between 0 and 20 km depth that is poorly studied. Understanding the source of variability in the amplitude of ground motion across Costa Rica is essential for improving building codes, fine-tuning Ground Motion Prediction Equations (GMPEs) and characterizing which regions are more susceptible to damage from earthquakes. This on-going study explores the variability in earthquake stress drop within these two distinct regions. We seek to better understand how the mechanical properties of the rocks in the Talamanca Mountain Range and the Tilaran Range influence the earthquake rupture mechanics and radiation of wave fields at frequencies compared to those responsible for negatively affecting buildings and infrastructures.

Session: Advances in Reliable Earthquake Source Parameter Estimation [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Sonia

Student Presenter: Yes

Invited Presentation: 

Poster Number: 26

Authors