Synthetic seismicity distribution in Guerrero–Oaxaca subduction zone, Mexico, and its implications on the role of asperities in Gutenberg–Richter law

Marisol Monterrubio-Velasco,F Ramón Zúñiga,Quetzalcoatl Rodríguez-Pérez,Josep De La Puente,Otilio Rojas,Armando Aguilar-Meléndez

doi:10.5194/gmd-13-6361-2020

Abstract

Abstract. Seismicity and magnitude distributions are fundamental for seismic hazard analysis. The Mexican subduction margin along the Pacific Coast is one of the most active seismic zones in the world, which makes it an optimal region for observation and experimentation analyses. Some remarkable seismicity features have been observed on a subvolume of this subduction region, suggesting that the observed simplicity of earthquake sources arises from the rupturing of single asperities. This subregion has been named SUB3 in a recent seismotectonic regionalization of Mexico. In this work, we numerically test this hypothesis using the TREMOL (sThochastic Rupture Earthquake MOdeL) v0.1.0 code. As test cases, we choose four of the most significant recent events (6.5 < Mw < 7.8) that occurred in the Guerrero–Oaxaca region (SUB3) during the period 1988–2018, and whose associated seismic histories are well recorded in the regional catalogs. Synthetic seismicity results show a reasonable fit to the real data, which improves when the available data from the real events increase. These results give support to the hypothesis that single-asperity ruptures are a distinctive feature that controls seismicity in SUB3. Moreover, a fault aspect ratio sensitivity analysis is carried out to study how the synthetic seismicity varies. Our results indicate that asperity shape is an important modeling parameter controlling the frequency–magnitude distribution of synthetic data. Therefore, TREMOL provides appropriate means to model complex seismicity curves, such as those observed in the SUB3 region, and highlights its usefulness as a tool to shed additional light on the earthquake process.

Highlights

The variation in seismicity distributions for different regions is a key input for probabilistic seismic hazard analysis (PSHA), as well as for other hazard determination approaches
The SA region 1 has an area of approximately 3207 km2 (Table 1), and Fig. 4 shows the observed and the sTochastic Rupture Earthquake MOdeL (TREMOL) synthetic seismicity curves
The frequency–magnitude distribution has a significant impact on the seismic hazard assessment

Summary

Introduction

The variation in seismicity distributions for different regions is a key input for probabilistic seismic hazard analysis (PSHA), as well as for other hazard determination approaches. A characteristic earthquake model implies a non-linear earthquake frequency–magnitude distribution, highly dominated by the occurrence of a preferred size event that induces low b values, or plateaus (Schwartz and Coppersmith, 1984; Wesnousky et al, 1983). In such cases, a GR relation is not a good representation, and it is not appropriate to describe the earthquake frequency relation for those particular regions (Aki, 1984; Parsons et al, 2018). Depending on the regional tectonics, the size distribution of earthquakes could generate a “mixed” frequency–magnitude distribution (Lay et al, 1982; Dahmen et al, 2001), where the frequency–magnitude fits a GR distribution at intermediate magnitudes, but large events (associated with the characteristic earthquake) depart from a linear GR relation (Lomnitz-Adler, 1985; Dalguer et al, 2004)

Methods

Results

Discussion

Conclusion