Skip to main content
USGS - science for a changing world
Advanced Search

Filters: Tags: geophysics (X) > Categories: Publication (X)

203 results (36ms)   

View Results as: JSON ATOM CSV
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
thumbnail
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
thumbnail
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
thumbnail
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
thumbnail
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
thumbnail
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
thumbnail
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
thumbnail
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
thumbnail
High-resolution aeromagnetic data acquired over the Albuquerque basin show widespread expression of faults that offset basin fill and demonstrate that the aeromagnetic method can be an important hydrogeologic and surficial mapping tool in sediment-filled basins. Aeromagnetic expression of faults is recognized by the common correspondence of linear anomalies to surficial evidence of faulting across the area. In map view, linear anomalies show patterns typical of extensional faulting, such as anastomosing and en echelon segments. Depths to the tops of faulted magnetic layers showing the most prominent aeromagnetic expression range from 0 to 100 m. Sources related to subtler fault expressions range in depths from 200...
Categories: Publication; Types: Citation; Tags: Geophysics
thumbnail
Using sounding curves based upon geologic models for a survey site, the latest measurement time for central induction transient soundings can be estimated for a given transmitter moment. Detectability limits are plotted on the apparent resistivity-time plots. Sounding points at earlier times than the limit are detectable, while those at later times are not. This procedure can be used during survey design to determine if features of the sounding necessary to the resolution of the geologic problem are detectable. Field measurements have shown that the method adequately predicts the latest measurement time.
Categories: Publication; Types: Citation; Tags: Geophysics
thumbnail
The utility of the seismoelectric method relies on the development of methods to extract the signal of interest from background and source-generated coherent noise that may be several orders-of-magnitude stronger. We compare data processing approaches to develop a sequence of preprocessing and signal/noise separation and to quantify the noise level from which we can extract signal events. Our preferred sequence begins with the removal of power line harmonic noise and the use of frequency filters to minimize random and source-generated noise. Mapping to the linear Radon domain with an inverse process incorporating a sparseness constraint provides good separation of signal from noise, though it is ineffective on noise...
Categories: Publication; Types: Citation; Tags: Geophysics


map background search result map search result map Compressional velocities from multichannel refraction arrivals on Georges Bank: northwest Atlantic Ocean Compressional velocities from multichannel refraction arrivals on Georges Bank: northwest Atlantic Ocean