Friese A.,German Research Center for Geosciences |
Kallmeyer J.,German Research Center for Geosciences |
Kitte J.A.,German Research Center for Geosciences |
Martinez I.M.,Institute Geofisica |
And 2 more authors.
Limnology and Oceanography: Methods | Year: 2017
Subsurface exploration relies on drilling. Normally drilling requires a drilling fluid that will infiltrate into the drill core. Drilling fluid contains non-indigenous materials and microbes from the surface, so its presence renders a sample unsuitable for microbiological and many other analyses. Because infiltration cannot be avoided, it is of paramount importance to assess the degree of contamination to identify uncontaminated samples for geomicrobiological investigations. To do this, usually a tracer is mixed into the drilling fluid. In past drilling operations a variety of tracers have been used, each has specific strengths and weaknesses. For microspheres the main problem was the high price, which limited their use to spot checks or drilling operations that require only small amounts of drilling fluid. Here, we present a modified microsphere tracer approach that uses an aqueous fluorescent pigment dispersion with a similar concentration of fluorescent particles as previously used microsphere tracers. However, it costs four orders of magnitude less, allowing for a more liberal use even in large operations. Its applicability for deep drilling campaigns was successfully tested during two drilling campaigns of the International Continental Drilling Program (ICDP) at Lake Towuti, Sulawesi, Indonesia, and Lake Chalco, Mexico. Quantification of the tracer requires only a fluorescence microscope or a flow cytometer. The latter allowing for high-resolution data to be obtained directly on-site within minutes and with minimal effort, decreasing sample processing times substantially relative to traditional tracer methods. This approach offers an inexpensive, rapid, but powerful alternative technique for contamination assessment during drilling campaigns. © 2017 Association for the Sciences of Limnology and Oceanography.
Rivera-Rios A.M.,Institute Geofisica |
Rivera-Rios A.M.,University of Adelaide |
Flores-Marquez E.L.,Institute Geofisica
Journal of Geophysics and Engineering | Year: 2012
This paper presents an algorithm based on the generalized Hough transform (GHT) to enhance geological structures in a 2D profile image constructed from ground-penetrating radar data. The proposed algorithm is applied over an edge representation image of the radargram; its local application (in Windows) allows us to identify structures and to obtain a global image delimiting the subsurface structures of interest. To show and validate the program, it was applied to two experimental cases: the first one is a profile of volcanic stratigraphic structures, and the second one consists of three buried pipes. The GHT algorithm enhances the main geological structures for both examples. Due to the use of a monostatic antenna in the case of buried pipes, a proper velocity analysis could not be done. As a consequence, the radargram remained under-migrated leaving some traces of diffraction hyperbola tails. These traces were detected by the GHT; therefore, a robust algorithm was designed to adjust a circle over these hyperbola traces. This secondary algorithm is called 'circular structure determination'. © 2012 Sinopec Geophysical Research Institute.
Calvo-Rathert M.,Polytechnic University of Mozambique |
Morales-Contreras J.,Institute Geofisica |
Goguitchaichvili A.,Institute Geofisica
Geochemistry, Geophysics, Geosystems | Year: 2016
Sixteen Miocene, Pleistocene, and historic lava flows have been sampled in Lanzarote (Canary Islands) for paleointensity analysis with both the Coe and multispecimen methods. Besides obtaining new data, the main goal of the study was the comparison of paleointensity results determined with two different techniques. Characteristic Remanent Magnetization (ChRM) directions were obtained in 15 flows, and 12 were chosen for paleointensity determination. In Thellier-type experiments, a selection of reliable paleointensity determinations (43 of 78 studied samples) was performed using sets of criteria of different stringency, trying to relate the quality of results to the strictness of the chosen criteria. Uncorrected and fraction and domain-state corrected multispecimen paleointensity results were obtained in all flows. Results with the Coe method on historical flows either agree with the expected values or show moderately lower ones, but multispecimen determinations display a large deviation from the expected result in one case. No relation can be detected between correct or anomalous results and paleointensity determination quality or rock-magnetic properties. However, results on historical flows suggest that agreement between both methods could be a good indicator of correct determinations. Comparison of results obtained with both methods on seven Pleistocene flows yields an excellent agreement in four and disagreements in three cases. Pleistocene determinations were only accepted if either results from both methods agreed or a result was based on a sufficiently large number (n>4) of individual Thellier-type determinations. In most Pleistocene flows, a VADM around 5 ×1022 Am2 was observed, although two flows displayed higher values around 9×1022 Am2. © 2016. American Geophysical Union.
Perez-Crespo V.A.,National Autonomous University of Mexico |
Arroyo-Cabrales J.,Laboratorio Of Arqueozoologia M En C Ticul Alvarez Solorzano |
Alva-Valdivia L.M.,Institute Geofisica |
Morales-Puente P.,National Autonomous University of Mexico |
Cienfuegos-Alvarado E.,National Autonomous University of Mexico
Geological Magazine | Year: 2012
Values for δ13C and δ18O obtained from molar samples from three individuals pertaining to Glyptotherium sp. from Cedral (San Luis Potosí, México) are provided and are utilized to infer general aspects of glyptodont diet and habitat. On average this animal showed a C3/C4 mixed diet, with a high consumption of C4 plants. Comparisons of the δ13CVPDB and δ 18OVPDB values for glyptodonts with horses, mastodons, mammoths and tapirs from the same locality show that glyptodonts from Cedral lived in an open habitat. © Copyright Cambridge University Press 2011.
Velasco Herrera V.M.,Institute Geofisica |
Mendoza B.,Institute Geofisica |
Velasco Herrera G.,National Autonomous University of Mexico
New Astronomy | Year: 2015
Total solar irradiance is the primary energy source of the Earth's climate system and therefore its variations can contribute to natural climate change. This variability is characterized by, among other manifestations, decadal and secular oscillations, which has led to several attempts to estimate future solar activity. Of particular interest now is the fact that the behavior of the solar cycle 23 minimum has shown an activity decline not previously seen in past cycles for which spatial observations exist: this could be signaling the start of a new grand solar minimum. The estimation of solar activity for the next hundred years is one of the current problems in solar physics because the possible occurrence of a future grand solar minimum will probably have an impact on the Earth's climate. In this study, using the PMOD and ACRIM TSI composites, we have attempted to estimate the TSI index from year 1000 AD to 2100 AD based on the Least Squares Support Vector Machines, which is applied here for the first time to estimate a solar index. Using the wavelet transform, we analyzed the behavior of the total solar irradiance time series before and after the solar grand minima. Depending on the composite used, PMOD (or ACRIM), we found a grand minimum for the 21st century, starting in ∼2004 (or 2002) and ending in ∼2075 (or 2063), with an average irradiance of 1365.5 (or 1360.5) Wm -2±1σ=0.3 (or 0.9) Wm-2. Moreover, we calculated an average radiative forcing between the present and the 21st century minima of ∼-0.1 (or -0.2) Wm-2, with an uncertainty range of -0.04 to -0.14 (or -0.12 to -0.33) Wm-2. As an indicator of the TSI level, we calculated its annual power anomalies; in particular, future solar cycles from 24 to 29 have lower power anomalies compared to the present, for both models. We also found that the solar activity grand minima periodicity is of 120 years; this periodicity could possibly be one of the principal periodicities of the magnetic solar activity not so previously well recognized. The negative (positive) 120-year phase coincides with the grand minima (maxima) of the 11-year periodicity. © 2014 Elsevier B.V. All rights reserved.
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 | Year: 2010
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.
Brudzinski M.R.,Miami University Ohio |
Hinojosa-Prieto H.R.,Miami University Ohio |
Schlanser K.M.,Miami University Ohio |
Cabral-Cano E.,Institute Geofisica |
And 3 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2010
The Oaxaca subduction zone is an ideal area for detailed studies of plate boundary deformation as rapid convergent rates, shallow subduction, and short trench-to-coast distances bring the thermally defined seismogenic and transition zones of the plate interface over 100 km inland. Previous analysis of slow slip events in southern Mexico suggests that they may represent motion in the transition zone, defining the downdip edge of future megathrust earthquakes. A new deployment consisting of broadband seismometers distributed inland along the Oaxaca segment provide the means to examine whether nonvolcanic tremor (NVT) signals can also be used to characterize the boundary between the seismogenic and transition zones. In this study, we established that NVT exists in the Oaxaca region based on waxing and waning of seismic energy on filtered day-long seismograms that were correlated across neighboring stations and were further supported by appropriate relative time moveouts in record sections and spectrograms with narrow frequency bands. Eighteen prominent NVT episodes that lasted upwards of a week were identified during the 15 months analyzed (June 2006 to September 2007), recurring as frequently as every 2-3 months in a given region. We analyze NVT envelope waveforms with a semiautomated process for identifying prominent energy bursts, and analyst-refined relative arrival times are inverted for source locations. NVT burst epicenters primarily occur between the 40-50 km contours for depth of the plate interface, except in eastern Oaxaca where they shift toward the 30 km contour as the slab steepens. NVT hypocenters correlate well with a high conductivity zone that is interpreted to be due to slab fluids. NVT is more frequent, shorter in duration, and located further inland than GPS-detected slow slip, while the latter is associated with a zone of ultra-slow velocity interpreted to represent high pore fluid pressure. This zone of slow slip corresponds to approximately 350°C-450°C, with megathrust earthquakes, microseismicity, and strong long-term coupling occurring immediately updip from it. This leaves NVT primarily in a region further inland from the thermally defined transition zone, suggesting that transition from locking to free slip may occur in more than one phase. Copyright 2010 by the American Geophysical Union.
Vazquez C. G.,National Autonomous University of Mexico |
Solis C. B.,National Autonomous University of Mexico |
Solleiro-Rebolledo E.,National Autonomous University of Mexico |
Goguitchaichvili A.,Institute Geofisica |
Morales C. J.J.,Institute Geofisica
Quaternary International | Year: 2016
In the Maya Lowlands region, along the Usumacinta River, Late Pleistocene-Holocene profiles exhibit sedimentary characteristics and soil formation processes, as a result of environmental conditions and human-environmental interactions. Here, we report a comprehensive environmental magnetic investigation on paleosols and sediments at the Tierra Blanca archaeological site which shows clear evidences of human occupation. The pedogenetical magnetic properties were characterized by rock magnetism studies to determine the composition, concentration and domain size distribution of magnetic minerals. The Late Pleistocene paleosols were formed under the influence of a humid climate, as shown by the presence of recent fine hematite formation, directly related to reduction-oxidation processes during Gleysol development. The transition from early to middle Holocene was obtained from a paleovertisol, dated as 2.34-2.3 ka, which showed a marked heterogeneity in its magnetic parameters due to continuous argilloturbation processes. The environmental conditions retrieved, indicate the presence of a drought period around 5.5 ka. The upper two paleosols were less developed and seems to be strongly affected by human activities during the Maya Classic period, dated between 1.14 and 0.97 ka. These soils were formed under more humid conditions, and yielded a magnetic mineralogy (hematite-magnetite-maghemite) due to incipient weathering and anthropic disturbance. © 2016 Elsevier Ltd and INQUA.
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 | Year: 2011
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.
Nelson C.E.,Consulting Geologist |
Proenza J.A.,University of Barcelona |
Lewis J.F.,George Washington University |
Lopez-Kramer J.,Institute Geofisica
Geologica Acta | Year: 2011
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.