Fault interactions and subsurface deformation in the Mexicali Valley: Implications for seismic hazard assessment at the México-USA border

This study investigates both previously known and unidentified subsurface deformation structures in the northwesternmost sector of the Mexicali Valley, México, near the international border with the USA. Several subsurface structures, including the Michoacán fault, have been identified between the Imperial-Laguna Salada fault zones by analyzing seismic reflection profiles, and their locations have been correlated with seismicity patterns. This study highlights the northward extension of the Michoacán fault beyond the border with the United States. While the trace of this fault has been reported elsewhere, some evidence has associated the existing deformation with a distinct, previously unknown structure; herein, named the Progreso Fault. The Dixieland Fault (USA) is not observed in México; however, the interaction of these faults plays a significant role in the regional seismic activity. Slip is distributed throughout the sector and is not concentrated on specific faults such as the Michoacán or Imperial. Faults with different orientations located between the Michoacán and Imperial Fault zones represent the potential northern limit of the Cerro Prieto Pull-Apart Basin. Additionally, several sub-basins have been identified in the study area. Although the two-dimensional seismic imagery used in this study does not allow for slip rate calculations on the faults, the observed structures provide valuable information about displacement and subsurface deformation in the region. The structures reported here contribute to the SCEC Community Fault Model (CFM), which integrates seismic reflection and other geological and geophysical data to define fault geometries. The CFM serves as a key input for physics-based fault system modeling and probabilistic seismic hazard assessments, including the Uniform California Earthquake Rupture Forecast (UCERF3). Consequently, the findings will aid in understanding regional fault interactions, providing essential constraints for future research and facilitating a better understanding of seismic hazards in the México-USA border region.