Controls of fault-system complexity and friction on seismicity in the El Salvador Fault Zone: results from physics-based earthquake cycle simulations

Paleoseismological evidence along the El Salvador Fault Zone (ESFZ) suggests the potential occurrence of earthquakes exceeding M_w7, raising critical questions about the seismic hazard of this complex strike-slip fault system in Central America. Here, we present the first application of physics-based earthquake cycle modelling to this region, aiming to assess whether such large events are physically plausible and to explore how fault-system complexity and frictional properties control seismicity patterns.

We perform long-term earthquake simulations using the MCQsim code (Zielke and Mai, 2023) on three alternative 3D fault models of the ESFZ, characterized by increasing structural complexity. Fault geometries, slip rates, and rakes are constrained using published geodetic, geological, and geomorphological data. A systematic sensitivity analysis explores the role of the critical slip distance (D_c) and the dynamic friction coefficient (μ_d) into the simulated seismicity statistics. Synthetic seismic catalogues are analysed, globally and segment-by-segment, in terms of maximum magnitude, interevent times, and frequency-magnitude distributions. 

Preliminary results, illustrated here for the simplest fault model and based on 10,000-year-long simulations for a systematic sensitivity analysis, indicate that maximum earthquake magnitudes strongly depend on frictional properties, while the critical slip distance mainly controls seismicity rates. Earthquakes exceeding M_w 7 are obtained only for low dynamic friction, associated with larger stress drops and more energetic ruptures. Increasing D_c reduces the number of small and moderate events, leading to longer interevent times and frequency–magnitude distributions that tend toward a characteristic earthquake behaviour. 

Ongoing work focuses on validating preferred synthetic catalogues for the different fault system complexity against instrumental seismicity and paleoseismological constraints in the ESFZ, including frequency-magnitude relations, recurrence intervals, magnitude-slip scaling, and rupture characteristics of the 2001 M_w6.6 earthquake. Overall, this study provides new insights into fault segment interaction, rupture jumping, and stress transfer along the ESFZ, contributing to improved seismic hazard assessment and supporting emergency management strategies in El Salvador and the broader Central American region.