Resumen

HERNANDEZ MADRIGAL, Víctor Manuel et al. Active faults in Zamora, Michoacán, Mexico: impact and monitoring. Invest. Geog [online]. 2024, n.115, e60915.  Epub 18-Mar-2025. ISSN 2448-7279.  https://doi.org/10.14350/rig.60915.

Subsidence due to groundwater overexploitation is one of the phenomena that most affects urban areas in Mexico located on unconsolidated deposits, as is the case in Zamora. This city, located in the northwestern part of the state of Michoacán on lacustrine and fluvial-lake sediments, is internationally recognized for its high production and processing of strawberries. This economic activity demands large volumes of high quality water, which has led to intense groundwater extraction. Subsidence in Zamora began to manifest itself in 2008 through surface and active geological faults, which, despite causing serious damage to infrastructure, had not been adequately studied. The objectives of this work are to map these structures for the first time and on a large scale; to quantify the rate of deformation and level of impact; and to analyze the relationship between the generation process of surface faults associated with differential subsidence and the fault system of regional tectonic origin and the trajectory of ancient tributaries. For this purpose, deformations in the urban infrastructure associated with differential subsidence were identified; a GPS monitoring system was implemented on ground control points strategically located on both fault blocks; the Degree of Urban Impact (GIU) was calculated from spatial relationships of intersection and proximity between the affected strip, fault axis and urban property; and the cartographic overlap between the surface faulting, current urban area, regional fault system, and trajectories of surface runoff from colonial times was evaluated. The results show that the city of Zamora is affected by four surface faults: “Centro”, “Colegio”, “Porvenir” and “Campestre”. The first two, older, present GIU of 0.36 and 0.42, respectively; maximum subsidence rate of 15.2 mm/year with a decelerating trend; and general NW-SE direction with a concave trajectory towards the south where the subsided block is located. The “Porvenir” fault with GIU of 0.31, has a WNW-ESE semi-concave trajectory towards the north where its down-dropped block is located, and maximum subsidence rate of 9.3 mm/year also in deceleration. In these three faults, the location of the sunken block and the scarp trajectory are not congruent with the geometry of the regional faulting, but with the ancient trajectory of the Duero river and Los Espinos channel (Centro and Colegio faults), and of the El Calvario drainage (El Porvenir fault), so their structural control is associated with paleochannels and their conditioning factors with fluvial deposits from pre-Hispanic and colonial times. In contrast, the Campestre surface fault, which is the youngest of all and also the one that has the greatest impact on the housing infrastructure (GIU=0.45), has a south-falling block and a WNW-ESE direction coincident with the Villa Fuerte deep fault and the geometry of the northern edge of the largest regional subsidence in the Zamora Valley. The active regional subsidence in combination with paleochannels that are very common in a valley of frequent floods such as the Zamora Valley, with graben-like basement geometry and intense groundwater extraction, is an important conditioning factor for the development of active and dynamic surface faults where they are generated and/or reactivated, develop, and “die” or stabilize. The mapping, degree of urban impact and rate of subsidence of the active faults of Zamora will allow the establishment of public policies aimed at planning the urban and agro-industrial growth of the region with a focus on disaster risk reduction.

Palabras llave : Duero river; sinking; faults; affectation; subsidence.

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