Geomorphic and paleoseismic evidence for active faulting along La Venta Fault, Guerrero, Mexican subduction Forearc

Understanding the potential earthquake activity of unknown active faults is crucial for assessing seismic hazards in subduction forearcs. Despite advancements, our knowledge of earthquakes on crustal faults away from plate boundaries, particularly in forearcs, remains incomplete. This study addresses this gap by utilizing paleoseismic records, conducting a lidar flight to develop a DTM in the highly vegetated mountains, remote and field mapping geomorphological features, performing a geophysical survey including electric resistivity, and excavating a paleoseismic trench, and dating with radiocarbon and optically stimulated luminescence, along the central section of the La Venta Fault, named Agua del Perro, in the Guerrero sector of the Mexican subduction Forearc. The trench revealed two-three rupturing events over the last 9000 years. The surface expression of this fault is subtle, characterized by a gentle scarp, minor stream offsets, and a shutter ridge. Our data show evidence of surface fault rupturing with lateral displacement of up to ~50 cm per event and vertical displacement of up to 25 cm. The most recent event occurred around the 14th century CE, registering a magnitude of Mw 6.6–6.8. Given the fault's location, our findings suggest a significant seismic risk to local communities along the fault and populations in larger cities like Chilpancingo, Acapulco, and Mexico City. The study also highlights potential damage to infrastructure, such as the La Venta Dam, and associated hazards, including flooding and rock falls. Regardless of the lack of time-limited instrumental seismicity, our results undoubtedly confirm the Holocene activity and seismogenic potential of the Agua del Perro section of the La Venta Fault. It emphasizes the importance of recognizing the potential hazard posed by crustal intraplate faults away from plate boundaries in the forearc mountains. Our findings underscore the significance of enhancing instrumental monitoring networks by incorporating remote sensing and field studies. This approach is crucial for identifying and characterizing active faults, especially in challenging environments like the one studied. • Paleoseismic evidence confirms Holocene activity along the Agua del Perro section of the La Venta Fault. • Trench excavation reveal 2–3 earthquakes on La Venta Fault in the last 9000 years. • Surface fault features include gentle scarp, minor offsets, pressure and shutter ridges. • Surface displacements of up to ~50 cm (lateral) and ~ 25 cm (vertical) were identified, indicating Mw 6.6–6.8 earthquakes. • Emphasized the need to enhance monitoring networks with remote sensing and field studies.