MSc defence by Álvaro Josué Campos Ramos
Álvaro Josué Campos Ramos from El Salvador, MSc Fellow in Geophysics at University of Iceland will present his MSc project on Friday 15th May at 13:10-13:22 at University of Iceland, Askja building, room 131. The presentation will be a part of the UI series "Open seminar at Masters-day of Natural Sciences".
The title of the project is:
Seismotectonic Characterization of the Ahuachapán Geothermal Field, El Salvador, Based on 1D Velocity Modeling, Earthquake Relocation, and Focal Mechanism Analysis
Álvaro's supervisors are:
Egill Árni Guðnason, Geophysicist, ÍSOR
Gylfi Páll Hersir, Geophysicist, Independent Consultant
Dr. Halldór Geirsson, Professor, University of Iceland
His external examiner is Bryndís Brandsdóttir, Retired Research Scientist, School of Engineering and Natural Sciences, Institute of Earth Sciences, University of Iceland
Abstract
Continuous seismic monitoring is a fundamental tool for understanding the structural framework, reservoir dynamics, and fluid–rock interactions in geothermal systems. In this study, a comprehensive seismological workflow has been applied to the Ahuachapán geothermal field in El Salvador consisting of velocity modeling, non‑linear probabilistic earthquake relocation, focal mechanism analysis, and migration studies to improve the characterization of subsurface processes. A new 1D velocity model has been obtained using the VELEST software, providing a more realistic representation of local lithological heterogeneities. The updated model was implemented in the NonLinLoc software to relocate a seismic catalog from January 2023 to July 2025, comprising 1,038 events, significantly reducing horizontal and vertical uncertainties and revealing spatially coherent seismic clusters aligned with major structural trends of the geothermal field. These results also allow an estimation of the brittle–ductile transition at 5-7 km depth, constrained using a 3D electrical resistivity model. The Vp/Vs ratio derived from the 1D model shows low values (1.43-1.50) in shallow layers and near the production zone, suggesting the presence of a steam‑dominated region. Focal mechanisms computed with the SKHASH software indicate a mixture of normal‑oblique, strike‑slip, and reverse‑oblique faulting, reflecting both the extensional regional stress regime and the local reservoir‑scale variations. Migration analyses reveal changes in propagation rates and complex temporal patterns, suggesting the interplay of permeability pathways, pore‑pressure diffusion. However, a larger number of events would be required to fully constrain the dominant migration mechanism. The b‑value analysis (0.68) indicates that the geothermal field is currently under relatively high differential stress. Cross‑correlation between seismicity and injection rates during the study period does not reveal a consistent or causal relationship. The integrated workflow developed in this study strengthens the structural interpretation of the Ahuachapán geothermal system and provides a methodological foundation that can be replicated in other geothermal fields in El Salvador to improve reservoir management and a further understanding of the geothermal systems.