1,195 research outputs found
Earthquake research: Premonitory models and the physics of crustal distortion
Seismic, gravity, and electrical resistivity data, believed to be most relevent to development of earthquake premonitory models of the crust, are presented. Magnetotellurics (MT) are discussed. Radon investigations are reviewed
Gravity measurements in support of long-baseline geodesy
Gravity data, believed to be relevant to unknown questions of earthquake premonitory crustal processes, are discussed and presented
Time-Dependent Seismology
The time variation of crustal velocities in tectonic regions is most reasonably attributed to stress induced variations in crack porosity. The decrease in V_p/V_s before earthquakes is due primarily to a large decrease in V_p. This supports the Nur dilatancy hypothesis but not the effective stress hypothesis. New data from the San Fernando region verify the V_p drop, show that this drop cannot be entirely due to source depth effects, and give strong support to the explanation of material property, or path effect, rather than source effect variations. Calculations show that the crack-widening model works even for mid crustal depths in saturated rock. Narrow cracks of low aspect ratio are required to satisfy the velocity and uplift constraints. The recovery of velocity prior to fracture can be due to fluid flow or crack closure. The t ∼ L^2 relation does not require diffusion. Diffusion of groundwater or crack closure leads to increased pore pressure and rock weakening. Observations of gravity, conductivity, and crustal distortions along with velocities should narrow the choice of models. The crust in regions of thrust tectonics is probably always dilatant to some degree. The aftershock region is smaller than the anomalous velocity region, which in turn must be smaller than the dilatant region. A simple relationship is derived for the relative sizes of the anomalous and aftershock regions
Time-dependent gravity in southern California, May 1974 - Apr 1979
Gravity measurements were coordinated with the long baseline three dimensional geodetic measurements of the Astronomical Radio Interferometric Earth Surveying project which used radio interferometry with extra-galactic radio sources. Gravity data from 28 of the stations had a single reading standard deviation of 11 microgal which gives a relative single determination between stations a standard deviation of 16 microgal. The largest gravity variation observed, 80 microgal, correlated with nearby waterwell variations and with smoothed rainfall. Smoothed rainfall data appeared to be a good indicator of the qualitative response of gravity to changing groundwater levels at other suprasediment stations, but frequent measurement of gravity at a station was essential until the quantitative calibration of the station's response to groundwater variations was accomplished
Far infrared maps of the ridge between OMC-1 and OMC-2
Dust continuum emission from a 6 ft x 20 ft region surrounding OMC-1 and OMC-2 were mapped at 55 and 125 microns with 4 ft resolution. The dominant features of the maps are a strong peak at OMC-1 and a ridge of lower surface brightness between OMC-1 and OMC-2. Along the ridge the infrared flux densities and the color temperature decreases smoothly from OMC-1 to OMC-2. OMC-1 is heated primarily by several optical and infrared stars situated within or just at the boundary of the cloud. At the region of minimum column density between OMC-1 and OMC-2 the nearby B0.5 V star NU Ori may contribute significantly to the dust heating. Near OMC-2 dust column densities are large enough so that, in addition to the OMC-2 infrared cluster, the nonlocal infrared sources associated with OMC-1 and NU Ori can contribute to the heating
Investigation of single crystal ferrite thin films
Materials suitable for use in magnetic bubble domain memories were developed for aerospace applications. Practical techniques for the preparation of such materials in forms required for fabrication of computer memory devices were considered. The materials studied were epitaxial films of various compositions of the gallium-substituted yttrium gadolinium iron garnet system. The major emphasis was to determine their bubble properties and the conditions necessary for growing uncracked, high quality films
Far infrared and submillimeter brightness temperatures of the giant planets
The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely
Relationship of the 1979 Southern California Radon Anomaly to a possible regional strain event
During the second half of 1979, anomalously high emanation of radon was recorded at two stations of the automated radon-thoron monitoring network operated by the W. K. Kellogg Radiation Laboratory of the California Institute of Technology. The two stations exhibiting major anomalies, Kresge and Dalton Canyon, are located approximately 30 km apart on the frontal fault system of the Transverse Ranges of southern California. At Kresge the anomaly began on June 21, 1979, and continued through December 1979. At Dalton Canyon the anomaly started about 3 weeks later and also continued through December 1979. At both sites the anomalous levels of radon decreased (but did not return entirely to normal values) shortly before October 15, 1979. During the week of October 15, 1979, a 6.6-M earthquake occurred about 290 km to the southeast of the two stations, and later in that week, earthquakes of magnitude 4.2 and 4.1 occurred at Malibu and Lytle Creek. The latter two events were within 60 km of the monitors. A radon-thoron monitor at Lytle Creek recorded no long-term anomaly but did record a sharp spikelike decrease in the radon level on October 13, 1979. Coincident with our observations of anomalous radon levels, other investigators have reported anomalies or suspected anomalies in several other geodetic, geophysical, and geochemical signals from the same general region. The rapid temporal development of several of the anomalies together with the large area over which they were observed suggests that a large-scale strain event took place which may have been responsible both for the widespread anomalies and for the seismicity that occurred in the region subsequent to the onset of the anomalies
Shoreline situation report, Middlesex County, Virginia
It is the objective of this report to supply an assessment, and at least a partial integration, of those important shoreland parameters and characteristics which will aid the planners and the managers of the shorelands in making the best decisions for the utilization of this limited and very valuable resource. The report gives particular attention to the problem of shore erosion and to recommendations concerning the alleviation of the impact of this problem. In addition we \u27have tried to include in our assessment some of the potential uses of the shoreline, particularly with respect to recreational use, since such information could be of considerable value in the way a particular segment of coast is perceived by potential users
Automated radon monitoring at a hard-rock site in the southern California transverse ranges
Data are presented from 20 months of near-real-time (three samples per day) radon monitoring at a hard-rock site in the Transverse Ranges of southern California. An annual cycle is evident in the data which is attributed to thermoelastic strains in the vicinity of the borehole site. Between April 1, 1977, and October 31, 1978, there were 11 earthquakes with magnitudes ≥2.0 within 25 km of the monitoring site. Three of these events appeared to be preceded by precursory signals, four were preceded by ‘possible’ precursory signals, and four were not preceded by any apparent precursors. Before the 4.6 M Malibu earthquake of January 1, 1979, a ‘possible’ precursory signal sequence of 40–50 days' duration was observed
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