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Vergnolle M.,Joseph Fourier University | Vergnolle M.,French National Center for Scientific Research | Walpersdorf A.,Joseph Fourier University | Kostoglodov V.,National Autonomous University of Mexico | And 4 more authors.
Journal of Geophysical Research: Solid Earth

The world's largest observed Slow Slip Events (SSE) occurred in 2001-2002 and 2006 in the Guerrero subduction zone, Mexico. Using an improved GPS processing that accounts for time-varying atmospheric phenomena as well as oceanic, atmospheric and hydrologic loading corrections, the 11 year GPS position time series in Guerrero show a noise reduction of ∼50% with respect to previous studies. Thanks to the improved position time series and, in particular, the simultaneous analysis of the three-dimensional GPS observations, we can provide new information about SSEs in the studied area. First, we detect seven nonperiodic anomalous displacements with subcentimeter amplitude, but no quasi-annual anomalies as proposed previously. The displacements seem to occur simultaneously with the observed peaks of non-volcanic tremor activity in the area. Second, we refine the characteristics of the two major SSEs in terms of timing, duration, and cumulative displacements, and highlight the complex surface spatiotemporal evolution of the displacements during these SSEs. In particular, we observe a clear initiation phase for the 2006 SSE as well as ending phases for both large SSEs. The ending phase shows a strong deceleration of the anomalous displacements with respect to the main displacement phase already observed, for the 2001-2002 and 2006 SSEs. The duration of the SSEs increases by 30-40% including the initiation and ending phases. For the 2006 SSE, the main displacement phase also shows spatiotemporal complexity. Our results demonstrate the need for improved three-dimensional GPS processing technique in order to undertake detailed studies of SSEs. Copyright 2010 by the American Geophysical Union. Source

Briseno-Ruiz J.V.,National Autonomous University of Mexico | Herrera-Zamarron G.D.S.,Institute Geofisica | Junez-Ferreira H.E.,National Autonomous University of Mexico
Tecnologia y Ciencias del Agua

It is essential to measure groundwater levels for long periods of time in order to estimate groundwater availability and its evolution. However, economic resources are a limitation to gathering enough data to estimate the evolution of these levels with certainty. Therefore, methods are required to design groundwater monitoring networks so as to effectively use the economic resources available for monitoring. The Herrera and Pinder method (Herrera, 1998) for the optimal design of groundwater quality sampling networks, applied by Herrera et al. (2001) and by Herrera and Pinder (2005), has several advantages: it allows for optimally selecting both monitoring positions and monitoring times; the information from the monitoring network enables obtaining estimates in space and time and; the method uses a flow and transport model that synthesizes knowledge about the characteristics of the aquifer, the groundwater flow dynamics and the groundwater quality problem, as well as knowledge about the laws of physics. This work tests, for the first time, a modification of the original method for the design of groundwater level monitoring networks. A synthetic case is presented in which the network is designed for a single time, assuming steady-state flow. The results indícate that the methodology proposed by Herrera and Pinder has good prospectsfor successful application to the optimal design of groundwater level monitoring networks. Source

Perez-Crespo V.A.,National Autonomous University of Mexico | Schaaf P.,National Autonomous University of Mexico | Solis-Pichardo G.,National Autonomous University of Mexico | Arroyo-Cabrales J.,Laboratorio Of Arqueozoologia M En C Ticul Alvarez Solorzano | And 2 more authors.
Geological Magazine

By using strontium isotopic ratios of dental enamel from molars, we were able to reconstruct the migration context for three individuals of a Columbian mammoth population (Mammuthus columbi) around Laguna de las Cruces, San Luis Potosí, central México. A three-step leaching procedure was applied to eliminate secondary Sr contributions in the molar enamel. One of the studied individuals showed 87Sr/86Sr ratios similar to those obtained from soils and plants from Laguna de las Cruces and was identified as local, whereas the other two mammoths had different molar 87Sr/86Sr values, indicative of migration and mobility contexts. ©Cambridge University Press 2016. Source

Kundu B.,National Geophysical Research Institute | Legrand D.,Institute Geofisica | Gahalaut K.,National Geophysical Research Institute | Gahalaut V.K.,National Geophysical Research Institute | And 5 more authors.

A 6 day duration earthquakes swarm occurred in the Andaman Sea, 31 days after the giant 2004 Sumatra-Andaman earthquake (Mw 9.2). The swarm occurred less than 100 km from the eastern edge of the 2004 earthquake rupture and is the most energetic ever recorded in the world. The earthquakes swarm appear to have occurred on en echelon fault system bounded by the two main right-lateral strike-slip faults, namely, the Seulimeum Strand of Sumatra Fault system (SEU) and the West Andaman Fault (WAF). At the beginning of the swarm, earthquakes with predominantly strike-slip focal mechanisms occurred which were followed by earthquakes with predominantly normal faulting focal mechanisms having significant deviatoric component. High b value, presence of double slope in the Gutenberg-Richter relation, presence of monogenetic submarine volcanoes in the region of the swarm and the earthquake focal mechanisms suggest that the swarm was of volcano-tectonic origin and fluid flow played an important role in its occurrence. Indeed, our modeling suggests that it was triggered by the 2004 Sumatra-Andaman earthquake through poroelastic relaxation of the coseismic stresses. © 2012. American Geophysical Union. All Rights Reserved. Source

Nelson C.E.,Consulting Geologist | Proenza J.A.,University of Barcelona | Lewis J.F.,George Washington University | Lopez-Kramer J.,Institute Geofisica
Geologica Acta

The Greater Antilles host some of the world's most important deposits of bauxite and lateritic nickel as well as significant resources of gold and silver, copper, zinc, manganese, cobalt and chromium. Beginning in Jurassic time, sedimentary exhalative base metal deposits accumulated in marine sedimentary rift basins as North and South America drifted apart. With the onset of intraoceanic subduction during the Early Cretaceous, a primitive (tholeiitic) island arc formed above a southwesterly-dipping subduction zone. Podiform chromite deposits formed in the mantle portion of the supra-subduction zone, directly above subducted Proto-Caribbean oceanic lithosphere. Within the nascent island arc, bimodal-mafic volcanogenic massive sulfide deposits formed in a fore-arc setting; mafic volcanogenic massive sulfide deposits formed later in mature back-arc basins. The Pueblo Viejo gold district, with five million ounces in production and twenty million ounces in mineable reserves, formed at 108-112Ma, in an apical rift or back-arc setting. By Late Cretaceous time, calc-alkaline volcanism was well established along the entire length of the Greater Antilles. Volcanogenic massive sulfide deposits including shallow submarine deposits characteristic of the primitive island arc gave way to porphyry copper and epithermal precious metal deposits typical of the mature island arc. Oblique collision of the Greater Antilles with North America began in the Late Cretaceous in Cuba and migrated eastward. Orogenic gold and tungsten deposits that formed during the collision event are preserved in ophiolites and in metamorphic core complexes. Since the Eocene, regional tectonism has been dominated by strike-slip motion as the North American continent moved westward relative to the Caribbean Plate. Large nickel-cobalt laterite deposits were formed when serpentinites were exposed to weathering and erosion during the mid-Tertiary. Bauxite deposits were derived from the weathering of volcanic ash within a carbonate platform of Eocene to Miocene age. Source

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