In the north Baja California and western Sonora region exists an important set of geologic faults, some of which extend southeast through the Gulf of California. These faults, which are part of the main border between the Pacific and North America tectonic plates, generate earthquakes of $Mw$ slightly over 7.0. An example of this is the $Mw$ 7.2 El Mayor–Cucapah earthquake of 4 April 2010. This and other past earthquakes caused severe damage and much concern among the inhabitants at both sides of the Mexico–US border. The Northwest Mexico Seismic Network (RESNOM) is a subnetwork of Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California (CICESE’s) network. RESNOM was designed to collect digital information from local and regional earthquakes that occur in the northern Baja California–western Sonora region. Although the design and installation of the network began in 1977, effective seismic monitoring began in June 1980. Through the years, RESNOM evolved from short‐period to broadband seismometers, accelerographs, and Global Positioning System (GPS) receivers collocated at each site. A description of this subnetwork and of some of the results obtained are presented here.

We have analyzed all available continuous Global Positioning System (cGPS) and campaign‐mode GPS data from northern Baja California, Mexico, covering the 1993.1–2010.1 period to obtain a consistent interseismic velocity field to derive a continuous strain‐rate field. The analysis shows concentrations of high strain rate along the Imperial/Cerro Prieto fault system extending from the Salton Sea to the Gulf of California, with strike‐slip faulting consistent with principal strain axes direction within the area of largest historical and instrumental seismic release. We translated the strain rate into geodetic moment accumulation rate to evaluate the potential of seismic activity of the region and compare with the actual seismic release of historical and instrumental earthquake catalog. Comparison of regional moment accumulation rate based on geodesy ($M˙0g=6.3±1.3×1018N·m/yr$) to the corresponding moment release rate by earthquakes ($M˙0s=2.7±0.8×1018N·m/yr$) highlights a moment rate deficit equivalent to an $Mw$ 7.5–7.8 earthquake. As part of this accumulated moment was released by the recent 2010 $Mw$ 7.2 El Mayor–Cucapah earthquake, these results can provide input constraints on earthquake forecasts for the northern Baja California fault system.

In this work, we investigate the April 4, 2010, M_w 7.2 El Mayor Cucapah (EMC) earthquake. Existing studies modeled the EMC area as an elastic half‐space in a homogeneous or vertically layered structure, which, along with differences in data and inversion methodologies, led to considerable variability in the resultant fault slip models. To investigate the EMC earthquake more realistically, we first examine how published coseismic fault slip models have approached the problem and what are their findings, then we select the optimal geometry and slip of one most recent and comprehensive coseismic fault slip model, obtained through analytical inversions, and adapt them in a three‐dimensional finite element numerical environment where we assess the effects of topography and material heterogeneities. Numerically optimized slip models are obtained via joint inversion of GPS, interferometric synthetic aperture radar, and subpixel offset data sets. We find the effect of topography to be negligible while the inclusion of material heterogeneities enhances the slip at depth, as might be expected where the medium has higher rigidity, and better fits the displacements at both near and far field, especially around the Salton Sea area. The match with geodetic data is significantly improved when the fault slip is increased at the fault planes close to the epicenter and deeper at the southernmost plane, with respect to the slip of the chosen analytical model. Our findings suggest that this earthquake was associated with a higher and more spatially concentrated slip than previously thought implying a greater stress drop at depth.

The Cerro Prieto basin, a tectonically active pull-apart basin, hosts significant geothermal resources currently being exploited in the Cerro Prieto Geothermal Field (CPGF). Consequently, natural tectonic processes and anthropogenic activities contribute to three-dimensional surface displacements in this pull-apart basin. Here, we obtained the Cerro Prieto Step-Over 3D surface velocity field (3DSVF) by accomplishing a weighted least square algorithm inversion from geometrically quasi-orthogonal airborne UAVSAR and RADARSAT-2, Sentinel 1A satellite Synthetic Aperture-Radar (SAR) imagery collected from 2012 to 2016. The 3DSVF results show a vertical rate of 150 mm/yr and 40 mm/yr for the horizontal rate, where for the first time, the north component displacement is achieved by using only the Interferometric SAR time series in the CPGF. Data integration and validation between the 3DSVF and ground-based measurements such as continuous GPS time series and precise leveling data were achieved. Correlating the findings with recent geothermal energy production revealed a subsidence rate slowdown that aligns with the CPGF’s annual vapor production.

El Mayor-Cucapah earthquake Mw 7.2 on April 4, 2010, occurred on Mexicali Valley near the international border between California, USA and Baja California, Mexico. The objective of this paper was to examine GPS as a complementary tool for seismic studies and to estimate earthquake seismic moment and Mw. For this purpose the capabilities of high-rate GPS (5 Hz) data located in the northern part of the seismic rupture has been explored to obtain the kinematic coseismic displacements. GPS data were processed using Precise Point Positioning method with GIPSY-OASIS II software, then applying the Fast Fourier Transform to the position time series, spectral parameters, seismic moment and Mw were calculated. A good agreement was found in terms of signal correlation of the GPS displacements, by comparing strong-motion seismic records integrated to displacement, using filtering parameters for two sets of instruments. Kinematic GPS displacement spectra clearly shows the low frequency displacement spectral level (~0.2 Hz) when compared with double integration of strong-motion data. It is easy to calculate the static coseismic motion from GPS data, however it is very difficult to calculate it from strong-motion data. A simple earthquake source model is suitable for the GPS dataset used in this work, estimated on Mw=7.19±0.13, was in according with Mw 7.2 obtained in other studies of the El Mayor-Cucapah earthquake.