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

146 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 Guatemala, Central America, ERT, Geophysics, Paleoseismology (1) Earth and Environmental Sciences, School of Science and Engineering, University of Missouri-Kansas City, Kansas City, MO U.S.A. (2) Institute of Geological Sciences, Friedrich-Schiller Universität Jena, Jena, Germany (3) Ingeotecnia, Ciudad de Guatemala, Guatemala (4) Centro de Estudios Superiores de Energía y Minas, Facultad de Ingeniería, Universidad de San Carlos de Guatemala, Guatemala (5) Millennium Institute on Volcanic Risk Research—Ckelar Volcanoes, Antofagasta, Chile Dollens, Aleigha (1) Niemi, Tina (1) Torres Ewert, Ivana (1,5) Lee, Jejung (1) Grützner, Christoph (2) Pérez Arias, Carlos (3) Flores Beltetón, Omar (4) ELECTRICAL RESISTIVITY TOMOGRAPHY IMAGING OF THE MOTAGUA FAULT ALONG THE 1976 EARTHQUAKE RUPTURE IN GUATEMALA A B S T R A C T The Motagua fault is a sinistral, strike-slip fault that forms part of the North American-Caribbean plate boundary. A 230-km- long segment of the Motagua Fault ruptured in the 1976 M7.5 Guatemala earthquake. We collected Electrical Resistivity Tomography (ERT) data using the Wenner array method at three locations (La Laguna, Gualán, and Estanzuela) where the 1976 ground rupture was exactly located using historical photographs and an extant offset canal. The data were processed using RES2DINV software to develop an inverse model with topographic corrections. At La Laguna and Gualán, the Motagua fault is defined by a 20-30 m wide zone with either a high or low resistivity, respectively. At Estanzuela, the fault appears buriedwith low resistivity sag pond material tilted toward the south. While the historical photographs of the 1976 rupture define a single, narrow rupture mole track, the subsurface data indicate additional parallel strands of the fault accommodate the deformation. I N T R O D U C T I O N The transform plate boundary that separates the North American and Caribbean plates is located in Guatemala. The Motagua fault is a left-lateral, strike- slip fault that accommodates part of the motion acrossthisboundary.OnFebruary4,1976,aM7.5earthquakeoccurred with a nearly continuous surface rupture of approximately 230 km (Plafker, 1976). This event was catastrophic to the communities and the economy of Guatemala, causing an estimated 23,000 casualties and leaving nearly one million people homeless (Espinosa, 1976). Despite the devastating impact of the 1976 earthquake, the long-term seismic potential of the Motagua fault is not fully understood.