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The conventional inversion of surface waves depends on modal identification of measured dispersion curves, which can be ambiguous. It is possible to avoid mode-number identification and extraction by inverting the complete phase-velocity spectrum obtained from a multichannel record. We use the fast simulated annealing (FSA) global search algorithm to minimize the difference between the measured phase-velocity spectrum and that calculated from a theoretical layer model, including the field setup geometry. Results show that this algorithm can help one avoid getting trapped in local minima while searching for the best-matching layer model. The entire procedure is demonstrated on synthetic and field data for asphalt...
Categories: Publication; Types: Citation; Tags: Geophysics
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Radioactivity measurements have played an important role in geophysics since about 1935, and they have increased in importance to the present. The most important areas of application have been in petroleum and uranium exploration. Radioactivity measurements have proved useful in geologic mapping, as well as in specialized applications such as reactor-site monitoring. The technological development of the method has reached a plateau, and the future of the method for some applications will depend upon development of more sophisticated data processing and interpretation. -Author
Categories: Publication; Types: Citation; Tags: Geophysics
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In this review of developments in the field of remote sensing from a geophysical perspective, the subject is limited to the electromagnetic spectrum from 0.4 mu m to 25cm. Three broad energy categories are covered: solar reflected, thermal infrared, and microwave.-from Authorremote sensing electromagnetic spectrum solar reflected thermal infrared microwave geophysics
Categories: Publication; Types: Citation; Tags: Geophysics
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Time-dependent gravimetric measurements can detect subsurface processes long before magma flow leads to earthquakes or other eruption precursors. The ability of gravity measurements to detect subsurface mass flow is greatly enhanced if gravity measurements are analyzed and modeled with ground-deformation data. Obtaining the maximum information from microgravity studies requires careful evaluation of the layout of network benchmarks, the gravity environmental signal, and the coupling between gravity changes and crustal deformation. When changes in the system under study are fast (hours to weeks), as in hydrothermal systems and restless volcanoes, continuous gravity observations at selected sites can help to capture...
Categories: Publication; Types: Citation; Tags: Geophysics
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The presence of strong surface-wave noise in surface microseismic data may decrease the utility of these data. We implement a technique, based on the distinct characteristics that microseismic signal and noise show in the τ‐p domain, to suppress surface-wave noise in microseismic data. Because most microseismic source mechanisms are deviatoric, preprocessing is necessary to correct for the nonuniform radiation pattern prior to transforming the data to the τ‐p domain. We employ a scanning approach, similar to semblance analysis, to test all possible double-couple orientations to determine an estimated orientation that best accounts for the polarity pattern of any microseismic events. We then correct the polarity...
Categories: Publication; Types: Citation; Tags: Geophysics
Geomechanical modeling of induced seismicity source parameters and implications for seismic hazard assessment, credited to Goertz-Allmann, BP, published in 2012. Published in Geophysics, volume 78, issue 1, in 2012.
Categories: Publication; Types: Citation, Journal Citation; Tags: Geophysics
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This dataset includes the magnetotelluric (MT) sounding data collected in 2006 in the Southern San Luis Valley, Colorado. The U.S. Geological Survey conducted a series of multidisciplinary studies, including MT surveys, in the San Luis Valley to improve understanding of the hydrogeology of the Santa Fe Group and the nature of the sedimentary deposits comprising the principal groundwater aquifers of the Rio Grande rift. The shallow unconfined and the deeper confined Santa Fe Group aquifers in the San Luis Basin are the main sources of municipal water for the region. The population of the San Luis Valley region is growing rapidly and water shortfalls could have serious consequences. Future growth and land management...
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Velocities were obtained from unreversed, refracted arrivals on analog records from a 48‐channel, 3.6-km hydrophone cable (3.89 km from the airgun array to the last hydrophone array). Approximately 200 records were analyzed along 1500 km of ship track on Georges Bank, northwest Atlantic Ocean, to obtain regional sediment velocity distribution to a depth of 1.4 km below sea level. This technique provides nearly continuous coverage of refraction velocities and vertical velocity gradients. Because of the length of the hydrophone cable and the vertical velocity gradients, the technique is applicable only to the Continental Shelf and the shallower parts of the Continental Slope in water depths less than 300 m. Sediment...
Categories: Publication; Types: Citation; Tags: Geophysics
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This dataset includes the magnetotelluric (MT) sounding data collected in 2009 in and near the San Luis Basin, New Mexico. The U.S. Geological Survey conducted a series of multidisciplinary studies, including MT surveys, in the San Luis Basin to improve understanding of the hydrogeology of the Santa Fe Group and the nature of the sedimentary deposits comprising the principal groundwater aquifers of the Rio Grande rift. The shallow unconfined and the deeper confined Santa Fe Group aquifers in the San Luis Basin are the main sources of municipal water for the region. The population of the San Luis Basin region is growing rapidly and water shortfalls could have serious consequences. Future growth and land management...
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Hydrothermally altered rocks, particularly if water saturated, can weaken stratovolcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-traveled, destructive debris flows, which are the largest volcanic hazards for Mount Adams and Mount Baker. Evaluating the hazards associated with such alteration is difficult because much of the alteration is obscured by ice and its depth extent is unknown. Intense hydrothermal alteration significantly reduces the resistivity and magnetization of volcanic rock and therefore hydrothermally altered rocks are identified with helicopter electromagnetic and magnetic measurements at Mount Baker and Mount Adams. High resolution magnetic and electromagnetic...
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A hybrid fast Hankel transform algorithm has been developed that uses several complementary features of two existing algorithms: Anderson's digital filtering or fast Hankel transform (FHT) algorithm and Chave's quadrature and continued fraction algorithm. A hybrid FHT subprogram (called HYBFHT) written in standard Fortran-77 provides a simple user interface to call either subalgorithm. The hybrid approach is an attempt to combine the best features of the two subalgorithms to minimize the user's coding requirements and to provide fast execution and good accuracy for a large class of electromagnetic problems involving various related Hankel transform sets with multiple arguments. Special cases of Hankel transforms...
Categories: Publication; Types: Citation; Tags: Geophysics
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Gravity data were collected from 2006 through 2015 to assist in mapping subsurface geology in the southern San Luis Basin, northern New Mexico. This data release provides principal facts for 566 new gravity stations that were acquired to fill in gaps in the existing public gravity data coverage.
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This dataset consists of 102 magnetotelluric (MT) stations collected in 2012-2014 in the Rio Grande Rift and southern Rocky Mountains. The U.S. Geological Survey acquired these data to improve regional conductivity models of the western United States. This work is in support of studies of the effect of lithospheric modification on electrical resistivity structure and tectonic evolution of the western United States.
Categories: Data; Types: Citation, Map Service, OGC WFS Layer, OGC WMS Layer, OGC WMS Service; Tags: Carson National Forest, Colfax County, Colorado, Colorado Plateau, Dona Ana County, All tags...


map background search result map search result map Compressional velocities from multichannel refraction arrivals on Georges Bank: northwest Atlantic Ocean Magnetotelluric data, Southern San Luis Valley, Colorado, 2006: Station 2 Principal facts of gravity data in the southern San Luis Basin, northern New Mexico Magnetotelluric sounding data, station 1, Taos Plateau Volcanic Field, New Mexico, 2009 Mount Adams Electromagnetic and Magnetic Data Regional scale magnetotelluric data from the Rio Grande Rift and southern Rocky Mountains Mount Adams Electromagnetic and Magnetic Data Principal facts of gravity data in the southern San Luis Basin, northern New Mexico Compressional velocities from multichannel refraction arrivals on Georges Bank: northwest Atlantic Ocean Regional scale magnetotelluric data from the Rio Grande Rift and southern Rocky Mountains