The Santa Lucía River Basin Trough is located in the southern sector of the Eastern Republic of U... more The Santa Lucía River Basin Trough is located in the southern sector of the Eastern Republic of Uruguay and has an area of almost 6,000 km2. In this work, the depth to the basement in the SW sector of the Santa Lucia Basin (SLB) was determined, using geophysical methods of exploration. The interest of exploring this geological basin is to determine its depth, recognizing the possible existence of deep aquifers, and the feasibility of hydrothermalism. For this reason were acquired, processed, inverted, and interpreted 10 magnetotelluric (MT) soundings. A 3D inversion based on the ModEM code was performed, and a 2D inversion (NLCG) of the invariant determinant along a profile that crosses the study area was carried out; their comparison yields similar resistivity and structural models results. The resistivity modeling was complemented with a Bouguer anomaly map created from a gravimetric database of 157 stations. Our geophysical results indicate that the Santa Lucia trough deepens toward the E-NE, reaching sedimentary thicknesses that may exceed 950 m. Outside the studied sector, its depth increases according to the gravity minimum, toward the NE of the area. Therefore, sandy or deep fractured episodes could harbor hot springs, whose temperature, considering the normal geothermal gradient of 30 °C/km, would approximately be in the range of 36–40 °C.
SUMMARY In this study, we investigated correlations between electromagnetic and seismic signals o... more SUMMARY In this study, we investigated correlations between electromagnetic and seismic signals of the 2017 February 15 Veracruz, Mexico, earthquake (Mw = 4.8). We carried out a time–frequency misfit analysis based on the continuous wavelet transform in order to compare electric, magnetic and seismic records accurately. This analysis was performed for horizontal and vertical components separately. Our results from time–frequency misfit and goodness-of-fit criteria confirm the general similarity between seismic and electromagnetic signals both in frequency and time. Additionally, we studied the behaviour of peak amplitudes of seismoelectromagenetic records as a function of magnitude and distance. Our observations are in good agreement with previous studies, confirming scaling with magnitude and attenuation with distance. Radiated seismic energy estimations were performed with two methods: integration of velocity records and empirical Green function, respectively. Estimated energy magnitudes (4.35 < Me < 4.98) are consistent with reported seismic magnitudes for this event. We propose a method for determining electric and magnetic coseismic energies based on the concept of energy flux as implemented in the frequency domain by the integration of electromagnetic records. The calculated energies showed that the radiated seismic energy is much higher than the electric and magnetic energies.
Abstract Cuenca de la Independencia (CI) is a semi-arid basin in Central Mexico, subdivided into ... more Abstract Cuenca de la Independencia (CI) is a semi-arid basin in Central Mexico, subdivided into four administrative hydrogeological regions, and comprised of two hydrogeological units: a granular aquifer of lacustrine origin overlying a fractured acidic igneous aquifer. Although many geophysical soundings were carried out within the basin, no geophysical data exceeding 500 m of depth has ever been reported; the actual conceptual models were generated only from shallower geophysical studies, geological and hydrogeochemical mapping. We performed a geophysical survey in CI to determine the geometry of the hydrogeological units through Audio-Magnetotellurics (AMT), Time Domain Electromagnetics (TDEM), and Vertical Electrical Soundings (VES). Since the acquired data set from the different applied geophysical methods are multidimensional and band-limited, some well-known empirical relations between the applied methods were used to improve the subsurface imaging, turning data into broadband-integrated and space-time scaled into the MT frequency domain. We present a methodology on how to handle this integrated information through a 2-D inversion approach. The results reveal that, even though there are two hydrogeological units, they could not be vertically distinguished, thus is not possible to refute the previous idea of direct vertical communication between the two aquifers. Moreover, a clear lateral transition in resistivity models was not found, so the administrative division of CI would only obey political-administrative purposes.
Abstract Detachment of the Baja California peninsula from the North American plate altered the cr... more Abstract Detachment of the Baja California peninsula from the North American plate altered the crustal region between them, including an extension of the crust between the peninsula and Mexico's mainland. In the SE portion of this region Bahia de Banderas, a 60-km indentation in the littoral of Mexico, is a boundary region across which significant changes in topography, seismicity, seismic attenuation, trench subduction angle, continental platform width, geomagnetic field, and crustal thickness have been documented. Here we identify two additional, major discontinuities: one in gravity and the second in the regional electrical resistivity to 50-km depth, both associated with the region in which the crust changes from extended to un-extended. Under the former, we ratify and extend the presence of the oceanic slab obtained elsewhere with seismological determinations. Plate rollback is also reported in the boundary region. Gravity and electrical resistivity models locate the NW and SE limits of the rolled-back portion of the oceanic slab; within this region, we identify upwelling asthenospheric material. Bahia de Banderas region represents a major tectonic discontinuity, implying the existence of a continental sliver prolonging ~160 km into the San Blas basin north of the bay, the Tres Marias sliver, independent from the Jalisco block, in which crustal fragmentation processes appear to be still in progress. We argue that this sliver is tectonically different from the Jalisco block since at least the late Miocene, when extensional tectonics stretched and thinned its corresponding crust and lithosphere.
The Santa Lucía River Basin Trough is located in the southern sector of the Eastern Republic of U... more The Santa Lucía River Basin Trough is located in the southern sector of the Eastern Republic of Uruguay and has an area of almost 6,000 km2. In this work, the depth to the basement in the SW sector of the Santa Lucia Basin (SLB) was determined, using geophysical methods of exploration. The interest of exploring this geological basin is to determine its depth, recognizing the possible existence of deep aquifers, and the feasibility of hydrothermalism. For this reason were acquired, processed, inverted, and interpreted 10 magnetotelluric (MT) soundings. A 3D inversion based on the ModEM code was performed, and a 2D inversion (NLCG) of the invariant determinant along a profile that crosses the study area was carried out; their comparison yields similar resistivity and structural models results. The resistivity modeling was complemented with a Bouguer anomaly map created from a gravimetric database of 157 stations. Our geophysical results indicate that the Santa Lucia trough deepens toward the E-NE, reaching sedimentary thicknesses that may exceed 950 m. Outside the studied sector, its depth increases according to the gravity minimum, toward the NE of the area. Therefore, sandy or deep fractured episodes could harbor hot springs, whose temperature, considering the normal geothermal gradient of 30 °C/km, would approximately be in the range of 36–40 °C.
SUMMARY In this study, we investigated correlations between electromagnetic and seismic signals o... more SUMMARY In this study, we investigated correlations between electromagnetic and seismic signals of the 2017 February 15 Veracruz, Mexico, earthquake (Mw = 4.8). We carried out a time–frequency misfit analysis based on the continuous wavelet transform in order to compare electric, magnetic and seismic records accurately. This analysis was performed for horizontal and vertical components separately. Our results from time–frequency misfit and goodness-of-fit criteria confirm the general similarity between seismic and electromagnetic signals both in frequency and time. Additionally, we studied the behaviour of peak amplitudes of seismoelectromagenetic records as a function of magnitude and distance. Our observations are in good agreement with previous studies, confirming scaling with magnitude and attenuation with distance. Radiated seismic energy estimations were performed with two methods: integration of velocity records and empirical Green function, respectively. Estimated energy magnitudes (4.35 < Me < 4.98) are consistent with reported seismic magnitudes for this event. We propose a method for determining electric and magnetic coseismic energies based on the concept of energy flux as implemented in the frequency domain by the integration of electromagnetic records. The calculated energies showed that the radiated seismic energy is much higher than the electric and magnetic energies.
Abstract Cuenca de la Independencia (CI) is a semi-arid basin in Central Mexico, subdivided into ... more Abstract Cuenca de la Independencia (CI) is a semi-arid basin in Central Mexico, subdivided into four administrative hydrogeological regions, and comprised of two hydrogeological units: a granular aquifer of lacustrine origin overlying a fractured acidic igneous aquifer. Although many geophysical soundings were carried out within the basin, no geophysical data exceeding 500 m of depth has ever been reported; the actual conceptual models were generated only from shallower geophysical studies, geological and hydrogeochemical mapping. We performed a geophysical survey in CI to determine the geometry of the hydrogeological units through Audio-Magnetotellurics (AMT), Time Domain Electromagnetics (TDEM), and Vertical Electrical Soundings (VES). Since the acquired data set from the different applied geophysical methods are multidimensional and band-limited, some well-known empirical relations between the applied methods were used to improve the subsurface imaging, turning data into broadband-integrated and space-time scaled into the MT frequency domain. We present a methodology on how to handle this integrated information through a 2-D inversion approach. The results reveal that, even though there are two hydrogeological units, they could not be vertically distinguished, thus is not possible to refute the previous idea of direct vertical communication between the two aquifers. Moreover, a clear lateral transition in resistivity models was not found, so the administrative division of CI would only obey political-administrative purposes.
Abstract Detachment of the Baja California peninsula from the North American plate altered the cr... more Abstract Detachment of the Baja California peninsula from the North American plate altered the crustal region between them, including an extension of the crust between the peninsula and Mexico's mainland. In the SE portion of this region Bahia de Banderas, a 60-km indentation in the littoral of Mexico, is a boundary region across which significant changes in topography, seismicity, seismic attenuation, trench subduction angle, continental platform width, geomagnetic field, and crustal thickness have been documented. Here we identify two additional, major discontinuities: one in gravity and the second in the regional electrical resistivity to 50-km depth, both associated with the region in which the crust changes from extended to un-extended. Under the former, we ratify and extend the presence of the oceanic slab obtained elsewhere with seismological determinations. Plate rollback is also reported in the boundary region. Gravity and electrical resistivity models locate the NW and SE limits of the rolled-back portion of the oceanic slab; within this region, we identify upwelling asthenospheric material. Bahia de Banderas region represents a major tectonic discontinuity, implying the existence of a continental sliver prolonging ~160 km into the San Blas basin north of the bay, the Tres Marias sliver, independent from the Jalisco block, in which crustal fragmentation processes appear to be still in progress. We argue that this sliver is tectonically different from the Jalisco block since at least the late Miocene, when extensional tectonics stretched and thinned its corresponding crust and lithosphere.
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