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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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Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field values and locations. This dataset presents latitude, longitude, altitude, and magnetic-field values.
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Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field values and locations. This dataset presents latitude, longitude, altitude, and magnetic-field values.
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Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field values and locations. This dataset presents latitude, longitude, altitude, and magnetic-field values.
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Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field values and locations. This dataset presents latitude, longitude, altitude, and magnetic-field values.
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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
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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


map background search result map search result map Preliminary gravity inversion model of Frenchman Flat Basin, Nevada Test Site, Nevada Aeromagnetic data for Saddle Mountain, Idaho Aeromagnetic data for Sherbrooke-Lewiston, New Hampshire Aeromagnetic data for Amargosa-Death Valley, California Aeromagnetic data for Adirondack Mountains North, New York Survey Part 2 of 2 Aeromagnetic data for Southeast Ohio, Ohio Aeromagnetic data for San Jose, California Compressional velocities from multichannel refraction arrivals on Georges Bank: northwest Atlantic Ocean Aeromagnetic data for Saddle Mountain, Idaho Preliminary gravity inversion model of Frenchman Flat Basin, Nevada Test Site, Nevada Aeromagnetic data for San Jose, California Aeromagnetic data for Adirondack Mountains North, New York Survey Part 2 of 2 Aeromagnetic data for Sherbrooke-Lewiston, New Hampshire Aeromagnetic data for Amargosa-Death Valley, California Aeromagnetic data for Southeast Ohio, Ohio Compressional velocities from multichannel refraction arrivals on Georges Bank: northwest Atlantic Ocean