Characterization of seismicity and precursor monitoring in northern Baja California using RESNOM data

Abstract

Northern Baja California, Mexico, is part of the boundary between the Pacific and North American plates, and the relative motion between these plates causes seismicity that has attained a recorded magnitude M7.3. This seismicity represents a hazard for towns and cities located in this area and, in order to be able to contribute to the hazard estimation, we propose to establish monitoring of possible precursors to major earthquakes.We will use data from the RESNOM seismological network, operated by CICESE, to monitor the area between longitudes −117.4° and −114.5°, and latitudes 30.5° and 33.2°.Since the study area presents a complex array of seismogenic regions, we define three regions for monthly precursor monitoring, based on long-term epicentral spatial distributions, together with geological and tectonic considerations. We propose monthly monitoring because it is a good tradeoff between useful temporal definition and having enough events for evaluation of statistical measures.We are monitoring monthly two types of measures, those that can be directly evaluated from data for each month (number of events/day, released seismic moment/day, and average magnitude and depth), and measures requiring more processing and larger amounts of data (direct clustering, clustering from apparent velocities, Poisson entropy, and fractal dimensions D0, D1, and D2).We estimate that coverage is adequate from 2005 to date (June 2023), and monitoring of data over this period suggests that, for two of the regions, it may be possible to identify precursory activity before earthquakes with magnitudes M≥7.0 and, possibly M≥6.0. The third region, however, needs improved network seismographic coverage for monitoring to be effective. There are not enough recorded strong and major earthquakes to be able to estimate reliability for precursory signals yet.Monitoring will continue indefinitely and may evolve to consider more or different measures and/or regions. We hope that this monitoring may help in identifying regions of interest for detailed observation and, eventually, to help in the estimation of seismic hazard in northern Baja California.