|Title||Marine controlled-source electromagnetics with geothermal purposes; central Gulf of California, Mexico|
|Publication Type||Journal Article|
|Year of Publication||2019|
|Authors||Cordoba-Ramirez F., Flores C., Gonzalez-Fernandez A., Constable S, Pena-Dominguez G., Gomez-Trevino E.|
|Type of Article||Article|
|Keywords||csem; electrical-resistivity; field; Geology; Geothermal Exploration; Guaymas Basin; Gulf of California; heat-flow; inversion; marine csem; ridge; santa rosalia; surface; system|
We acquired and interpreted data from two controlled-source electromagnetic profiles, in the Gulf of California off the coast of Santa Rosalia, Baja California Sur, Mexico. This area is interesting from the geothermal point of view due to its proximity to the Guaymas Basin, the La Reforma Caldera, and the Las Tres Virgenes volcano, the first with intense submarine hydrothermal manifestations and the final one with a geothermal field in production. The survey consisted of the deployment of 10 Ocean Bottom Electromagnetic receivers, distributed along two similar to 14 km-long profiles. These sensors recorded the two horizontal components of the electric and magnetic fields. The source consisted of a horizontal 200 m electric dipole towed behind the vessel. The processed data were inverted to estimate the subsurface distribution of electrical resistivity using a finite-element two-dimensional multi-frequency program, resulting in adequate fits between observed and calculated data. To estimate how well the models are constrained by the data, sensitivity tests were applied to the models. The tests were based on the Jacobian matrix and a perturbation analysis of selected features of the model. They show that the model in its central part is well constrained by the data down to a depth of about 2.5 km. With the perturbation approach, 16 resistivity features out of the 19 tested turned out to be well constrained by the data. The estimated resistivity distribution was compared with the information obtained from other geophysical methods (bathymetry, gravity, and 2D multi-channel seismic reflection), resulting in reasonably good correlations between them. For the first profile, we find a remarkable similarity with the current conceptual models proposed in the literature for a volcanic geothermal system, where an altered conductive clay cap overlays another with higher electrical resistivity. The second profile shows agreements with anomalies detected with echo-sounder bathymetry suggesting the existence of hydrothermal manifestations. (C) 2019 Elsevier B.V. All rights reserved.