Four large earthquakes in the last 1700 years on the Motagua Fault, Guatemala

The sinistral strike-slip Motagua Fault in Guatemala is part of the North American-Caribbean plate boundary system. A magnitude 7.5 earthquake that occurred on the fault in 1976 caused 230 km of surface rupture, up to 3 m surface offset, and the demise of ca. 23,000 people. Knowledge of earlier large earthquakes on this fault is largely lacking, hampering our understanding of the tectonic regime and the associated hazards for a largely vulnerable population. We used historical archives, aerial and satellite imagery, shallow geophysics, drone lidar surveys, and field mapping to identify a site that holds a geological record of past movements of the fault. In a paleoseismological trench at La Laguna (Sanarate), we found evidence for four surface-rupturing earthquakes. A small bend in the fault trace causes localized oblique-slip motion on the fault, leading to vertically offset strata and colluvial wedge formation in the hanging wall. Radiocarbon dating, optically stimulated luminescence, and archaeological findings of Mayan ceramics and obsidian blades show that the earthquakes occurred in the last ca. 1700 years. This implies a recurrence interval of 400-500 years along this part of the plate boundary.