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

354 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E PATA Days 2024 K E Y W O R D S seismic hazards , Central America, transform fault, ground rupture, aseismic slip (1) Earth and Environmental Sciences, University of Missouri- Kansas City, Kansas City, MO U.S.A. (2) Department of Geosciences & Geological and Petroleum Engineering, Missouri University of Science and Technology, Rolla, MO U.S.A. (3) Department of Geological Sciences, University of Missouri, Columbia, MO U.S.A. (4) California State University of Fullerton, Fullerton, CA U.S.A. (5) Centro de Estudios Superiores de Energía y Minas, Facultad de Ingeniería, Universidad de San Carlos de Guatemala, Guatemala (6) Institute of Geological Sciences, Friedrich-Schiller Universität Jena, Jena, Germany (7) Ingeotecnia, Ciudad de Guatemala, Guatemala *Email: niemit@umkc.edu Tina M. Niemi (1) Trenton McEnaney (2) Francisco Gómez (3) Kenneth Álvarez (4) Jonathan Obrist Farner (2) Omar Flores Beltetón (5) Aleigha Dollens (1) Christoph Grützner (6) Jeremy Maurer (2) Carlos Pérez Arias (7) LIDAR, PALEOSEISMIC TRENCH, AND ERT DATA ACROSS THE 1976 EARTHQUAKE RUPTURE OF THE MOTAGUA FAULT AT GUALÁN, GUATEMALA A B S T R A C T The 1976 Guatemalan earthquake ruptured the left-lateral, strike-slip Motagua fault along the plate boundary separating the North American and Caribbean plates. Using maps, photos, 35 mm slides, and field notes from the U.S.G.S. archive of George Plafker, we relocated portions of the 1976 ground rupture and created a digital database. These data helped us to identify potential paleoseismic research sites. Two unmanned aerial system campaigns collected LiDAR data at six sites. Here, we report on relocation of a concrete irrigation canal that was offset by 93 cm in the 1976 earthquake at the Finca Los Limones site located 1.5 km east of Gualán and LiDAR, electrical resistivity tomographic (ERT), and paleoseismic trench data at the site. A microslope map derived from the LiDAR data highlight the vertical walls of the canal and shows that the canal is now offset by 1.65-1.80 m representing addition aseismic slip. The geomorphic expression of the fault at the site shows evidence of repeated fault slip including the presence of a sag pond, a linear depression, fault scarp, and offset channel and fluvial terraces. ERT data show that the fault zone has two narrowly spaced strands that are confirmed from trenching. A trench at the base of the 5-m-high fault scarp shows development of multiple inset fissures filled with dark brown, organic-rich soil. Dating of the paleoseismic record at this site has been difficult due to a lack of radiocarbon samples but down- warping and folding of buried soil surfaces show repeat rupture along the fault trace. Aseismic and coseismic slip along the fault trace may complicate how paleoearthquakes are defined along the Motagua fault.