Title: An Overview of Seismological Studies Carried Out in Costa Rica at Teleseismic, Regional, and Local Scales.
Abstract: This talk compiles several research projects conducted at OVSICORI, covering scales ranging from teleseismic and regional studies to detailed near-field analyses.
At the teleseismic scale, we document for the first time in the modern seismological era the dynamic triggering of microseismicity in Costa Rica. Using OVSICORI’s broadband seismic stations, to look for teleseismic events with dynamic stresses higher than 1.1 kPa from 2010 to February 2023. We identified a total of 25 events, with two prominent examples of instantaneous triggering during the arrival of surface waves: the 7.55 Mw Swan Islands earthquake in 2018 and the 7.8 Mw Turkey earthquake in 2023. Our results show that dynamically triggered seismicity primarily occurs in northern volcanic regions and along the southern Pacific subduction zone, indicating the presence of weakened fault zones in these areas.
At the regional scale, we analyzed Peak Ground Velocity (PGV) distributions resulting from the passage of surface waves from the previously mentioned 25 teleseismic events. Our findings revealed distinct high and low PGV zones across the country. Overlaying shallow seismicity data onto these PGV patterns, we observed clear clusters of seismic activity within these zones. This leads us to investigate whether fundamental differences exist in earthquake source parameters between regions of high and low PGV. Our ongoing research aims to understand the variability in earthquake stress drop and how rock mechanical properties influence rupture mechanics and the frequency content of seismic waves, particularly those affecting buildings and infrastructure.
In near-field investigations, we are actively monitoring a landslide in the Aguas Zarcas River, San Carlos, located in north-central Costa Rica. This landslide covers approximately 30 hectares, affecting an additional 40 hectares downstream, with an estimated volume of 10 million cubic meters. Classified as a complex, high-velocity rockslide resembling volcanic debris avalanches, this landslide has been continuously monitored since May 2024 through a deployment of nine Smart Solo seismic nodes. Over 1500 low-frequency earthquakes (LFEs) with seismic moment magnitudes Mw < 1.0 have been identified, indicating that the landslide is still active, and its deformation is modulated by gravitational forces and the slow deformation of the unstable mass. This scenario resembles a slow slip event, generating repeating earthquake families. By using landslides as natural laboratories, we can better understand near-field stick-slip processes and rate-and-state friction laws.
Biography: Sonia Hajaji Salgado is a geologist from Costa Rica who recently completed her bachelor’s degree. She has been working for two years as an ad-honorem student at OVSICORI, under the mentorship of Dr. Esteban Chaves. In 2025, Sonia officially joined OVSICORI as a seismologist, focusing her research on earthquake physics. Her primary interests include observational seismology, earthquake rupture dynamics, seismic source characterization, subduction zone processes, and the intriguing relationship between seismic and aseismic phenomena. Sonia’s recent projects have covered diverse topics such as the dynamic triggering of earthquakes in Costa Rica, understanding the influence of upper plate structures on earthquake stress drop in high and low ground-velocity zones, landslide monitoring, microseismicity studies in densely populated areas using nodal arrays, and exploring oceanic dynamic processes.
To join virtually: Zoom
Contact: soniahajaji@gmail.com
Recording: Zoom Recording (will be available within a week after the seminar)