Electrical resistivity tomography imaging of the Motagua Fault in Guatemala
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Abstract
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 two locations (Gualán and Estanzuela) where the 1976 ground rupture was exactly located using historical photographs and an offset concrete irrigation canal. The data were processed using RES2DINV software to develop an inverse model with topographic corrections. At Gualán, the Motagua fault is defined by a 7-m-wide low-resistivity zone. At Estanzuela, a low resistivity zone represents the northern faultcontrolled margin of the sag depression. While the historical photographs of the 1976 fault rupture define a single, narrow rupture mole track, ERT data indicate parallel fault strands and distributed shear in the subsurface. Aseismic slip (creep) along multiple fractures may also play a role in producing the low resistivity zones along the Motagua fault. The ERT data in this study indicate the presence of inactive borderline structures and distributed shear near the fault zone, extending beyond the main active fault strand.
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Introduction -- Methodology -- Gualán -- Estanzuela -- Discussion -- Conclusion
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M.S. (Master of Science)