Interaction between historical earthquakes in the seismic gap of Central Chile and the Marga-Marga crustal Fault: The seismic potential of the Valparaiso región.
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Date
2025
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Publisher
Universidad de Concepción
Abstract
The spatial distribution of earthquake ruptures along seismic segments is crucial for understanding the megathrust cycle in subduction zones. In central Chile, the segment between 32° and 34°S presents a concerning case: despite experiencing several moderate historical earthquakes, it has been identified as a seismic gap since the major 1730 event, which stands as the largest known earthquake in the region.
While subduction processes dominate plate convergence in this region, the role of continental crustal deformation adds another layer of complexity. Of particular interest is the Marga-Marga crustal fault, which runs beneath one of Vi˜na del Mar’s most populated areas.
Our research investigates the complex and poorly studied seismic history of this segment by estimating slip distributions and magnitudes for three significant events: the 1730, 1906 Valparaiso, and 1985 Algar robo earthquakes. We selected these specific events because the 1906 and 1985 earthquakes share similar deformation patterns surrounding the fault trace, which may indicate specific activation mechanisms. Ad ditionally, as we anticipate a future event with similar characteristics to the 1730 earthquake–for which no detailed fault response data exists–modeling this historical scenario provides valuable insights for future earthquake interactions. We combined historical data on vertical displacements and tsunami inundations with a stochastic approach using the logic-tree method. To enhance the reliability of our findings, we devel oped an uncertainty analysis framework that integrates clustering analysis of maximum slip locations with mean square error calculations, providing a robust assessment of historical earthquake characteristics.
Through Coulomb stress analysis using our preferred slip distributions, we found that historical subduc tion earthquakes could have triggered fault activation, a significant consideration since crustal earthquakes can produce more concentrated damage than subduction events of similar magnitude.
This comprehensive study lays the groundwork for more detailed investigations of seismic hazard in this densely populated region, particularly regarding the complex interaction between megathrust events and the Marga-Marga fault system. Our findings emphasize the need for further research to better understand the fault response to large subduction earthquakes.
Description
Tesis presentada para optar al grado de Magíster en Geofísica.
Keywords
Earthquake hazard analysis, Geophysical surveys, Fault zones