Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

358 PATA Days 2024 formed within pullapart basins as the transform fault developed in the Eocene. The rocks of the mountains both north and south of the Motagua valley are schistose gneiss, mica schist, marble, and minor amphibolite that mark complex tectonic suturing events in the Paleozoic and the Cretaceous. Serpentinite within the fault zone (Bruekner et al., 2009) may play a major in the Motagua fault rupture history and seismic potential. Fig. 4: A 10-cm contoured DEM image of the Gualán site derived from LiDAR imagery showing the linear depression formed along Motagua fault, south-facing scarp, sag pond, fluvial terraces (Qft1 and Qft2), channel offset, and location of the offset irrigation canal. The Motagua fault at the Finca Los Limones site in Gualán is marked by a linear depression across a series of fluvial terraces indicating repeated fault slip at the this location (Fig. 4). A high, south-facing fault scarp is clearly marked across the site, but a more subtle north-facing scarp also lies along the depression. A seasonal natural sag pond appears along the western side of the site. Cultural modifications include a dam across the sag and a pond on the fault, adjacent to the irrigation canal. The original canal offset measurements were reported as 93 cm while the side lines on the Gualán soccer field was offset by 89 cm (Plafker, 1976; Plafker et al., 1976). We relocated these sites in July 2021 (Fig. 5). In April 1976, a line of nail markers was placed as a reference at three sites including Gualán and a photo of new cracks developing along the ground rupture were documentd (Fig. 6). Bucknam et al. (1978) measured the offset of the Gualán canal and report three additional afterslip measurements approximately 100, 200, and 300 days after the earthquakes (Bucknam et al. 1978) with a maximum slip of 109 cm including 16 cm of afterslip. Field notes from Plafker (U.S.G.S. archive) show an annotated sketch map of the canal from October 5, 1977 which states “could not re- locate all pins at canal. Measured offset ~30 cm…Canal last required patching about 6 months earlier…abundant new cracks visible with small sinistral offsets (~2 cm). Canal offset by alinement of edges is about 121 cm.” This measurement is greater by an additional 12 cm than reported in the Bucknam et al. (1978) paper.