A premier field-based slip rate and total offset estimate for the Motagua Fault, Guatemala

The Motagua Fault in Guatemala is the southern one of two sinistral strike-slip faults that make up the North American-Caribbean plate boundary system. Both faults are known to produce large earthquakes, the most recent one being a magnitude 7.5 on the Motagua Fault that caused severe damages to the infrastructure of the country and about 23,000 deaths. Together both faults accommodate ca. 20 mm of slip per year. At present, the Motagua Fault is more active than the Polochic Fault to the north, taking up most of the slip, while in the past the contrary was the case. However individual slip rate estimates thus far are very vague and mainly based on GPS measurements. At the Río El Tambor site southwest of Cabañas, multiple river terraces are laterally offset by the Motagua Fault. We used optically stimulated luminescence and radiocarbon dating on these terraces to provide the first field-based estimate for the slip rate of the Motagua Fault. Additionally, we used satellite imagery, drone lidar surveys, and historical data to map and systematically evaluate offsets on geomorphic markers. These indicate that the total offset on the Motagua Fault is at maximum ca. 20 km and thus, the switch of the high slip rate from the Polochic to the Motagua Fault probably did not happen earlier than in the Pleistocene.