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Map of the Motagua Fault and our trench site
Picture: Christoph GrütznerThe Motagua Fault in Guatemala is part of the North American–Caribbean plate boundary. On 4 February 1976, rupture occurred during an M7.5 earthquake, in which 23,000 people were killed. Surface ruptures extending over 230 km were generated by the event. Despite the evident seismic hazard, the earthquake history of the fault has remained largely unknown. In a new studyExternal link, evidence for five surface-rupturing earthquakes within the past 1,300 years is presented. Paleoseismological trenching, geomorphological observations, and archaeological information from nearby sites were used to reconstruct the seismic history of the left-lateral Motagua Fault.
A paleoseismological trench was excavated at La Laguna near the western end of the 1976 surface rupture, where the strike-slip fault bends to the left. This bend results in local extension and introduces a vertical component of slip. At La Laguna, the 1976 event is characterized by the largest recorded displacement, exceeding 3 m of lateral slip and more than 80 cm of vertical offset.
Photomosaic of the trench walls and the trench logs.
Graphic: Christoph GrütznerAt the trench site, two dry stone walls are observed to be laterally offset: one by 3.4 m, as documented in 1976, and another by 4.8 m. This suggests that two earthquakes are recorded by the latter wall. Evidence for at least two events is also preserved by the fault scarp, as it is 1.2 m high, whereas the 1976 displacement was only ~80 cm.
A 7 m-long, 2 m-deep trench was excavated by hand, and the main fault zone was identified along with several colluvial wedges. These wedges are sedimentary features that are formed on the hanging wall of a fault when the vertical scarp created by an earthquake rapidly collapses after the event. Charcoal pieces and pottery sherds were collected, which helped to constrain the timing of past surface-rupturing earthquakes. In total, five events—including the 1976 earthquake—are inferred to have occurred over the past 1,300 years.
To further refine the earthquake chronology, excavation reports from the archaeological sites of Quiriguá and Mixco Viejo, two major Maya sites located along the fault trace, were examined. Evidence such as collapsed structures, phases of intensive repair, building reinforcements, and broader societal changes is interpreted as indicating episodes of strong seismic activity. Three earthquakes are inferred to have occurred between the 8th and 13th centuries, and two between the 18th and 20th centuries, separated by an approximately 600-year interval without surface ruptures on the Motagua Fault. A macroseismic database was also consulted to identify historical earthquakes that could correspond to the penultimate event; several 18th-century earthquakes are considered plausible candidates.
An average recurrence interval of approximately 250–330 years for major earthquakes on the Motagua Fault is indicated by the results. However, earthquake recurrence is found to be highly irregular: some events are separated by less than 250 years, whereas others are divided by gaps of up to 600 years. A similar pattern has been documented for the Polochic Fault based on seismite records. The causes of this variability remain uncertain but may involve interactions between the Motagua and Polochic Faults, or periods of aseismic slip or fault creep.
The new study is available open access here: https://www.nature.com/articles/s43247-026-03271-yExternal link
The work by Christoph Grützner is financed by DFG project 529303576 “Active tectonics of the Caribbean-North American plate boundary in GuatemalaExternal link”. Tina Niemi has NSF Grant OISE-2153715 for the Guatemala GeoHazards IRES program.
In a recent review paper with a contribution of Christoph Grützner, Clark et al. summarize 50 years of research since the 1976 earthquake: https://pubs.geoscienceworld.org/ssa/bssa/article/doi/10.1785/0120250268/725778/A-Fiftieth-Year-Retrospective-on-the-1976-Mw-7-5External link