34-1 Mechanical interactions between extensional and strike slip faults in the Paso Inferior Accommodation Zone, Sierra Cucapá

Session: Recent Advances in the Gulf of California Oblique Rift: Offshore and Onshore Studies // Avances Recientes en el Rift Oblicuo del Golfo de California: Estudios Marinos y Terrestres (Posters)

Poster Booth No.: 1

Presenting Author:

Iris Gauna Sauceda

Authors:

Gauna Sauceda, Iris Lucia¹, Fletcher, John M.², Hinojosa Corona, Alejandro ³, Rösler, Boris⁴, Spelz, Ronald M.⁵, Carranza Chávez , Francisco J⁶

(1) Depto. de Geología, CICESE, Ensenada, Baja California, Mexico, (2) Depto. de Geología, CICESE, Ensenada, Baja California, Mexico, (3) Depto. de Geología, CICESE, Ensenada, Baja California, Mexico, (4) Depto. de Sismología, CICESE, Ensenada, Baja California, Mexico, (5) Universidad Autónoma de Baja California, Ensenada, Baja California, Mexico, (6) Depto. de Electrónica y Telecomunicaciones, CICESE, Ensenada, Baja California, Mexico,

Abstract:

The Laguna Salada region, located in the northeastern Baja California Peninsula, is a tectonic domain within the Gulf of California extensional province. It has undergone significant deformation associated with transtensional shear between the Pacific and North American plates. This region has been widely studied because it contains two major extensional fault systems with opposing senses of tectonic transport, separated by the strike-slip Laguna Salada fault.

The Paso Inferior accommodation zone, located northwest of the Sierra Cucapá, is juxtaposed between two distinct extensional fault systems with opposing polarities of tectonic transport. In this study, we compile new and previously published structural data to characterize the geometry and kinematics of faults in the region. Detailed mapping enabled the identification of cutoff lines and piercing points, which were used to document a pronounced northward-decreasing gradient in finite offset along the Borrego fault, ranging from ~6 to ~1.5 km. This long-term slip pattern on the Borrego fault was replicated during the 2010 Mw 7.2 El Mayor–Cucapah earthquake, when rupture was diverted from the northern Borrego fault and transferred to the Paso Superior fault. Despite kinematic variations among the analyzed faults, all exhibit subparallel T-axis orientations trending ENE, demonstrating that a single seismic event can activate faults with variable orientations.

Observed slip directions were compared with theoretical slip directions calculated using the proposed regional stress tensor (S_V = 280/90, S_H = 355/0, S_h = 85/0, and Φ = 0.9), revealing low angular misfit. These results indicate that the geometry and kinematics of the analyzed faults are analogous to those of other fault systems within the Gulf of California extensional province, and that the fault network cutting the Sierra Cucapá accommodates part of the three-dimensional deformation associated with the plate boundary.

At present, the west-directed system controls subsidence of the Laguna Salada basin and greatly outpaces slip on faults of the east-directed system, which commonly form antithetic structures relative to the existing topography. Detailed mapping has identified beheaded strands of west-directed faults that have been transported eastward into the Sierra Cucapá across faults of the east directed system. These structural relationships indicate episodic accelerations and decelerations of extensional fault systems with opposing senses of tectonic transport as they interact along their line of juxtaposition.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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