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D. C. Ross

Publications and source records attributed to D. C. Ross.

17 recordsLinked to original sources
USGS1983

Summary of workshops concerning regional seismic source zones of parts of the conterminous United States, convened by the U.S. Geological Survey, 1979-1980, Golden, Colorado

Workshops were convened by the U.S. Geological Survey to obtain the latest information and concepts relative to defining seismic source zones for five regions of the United States. The zones, with some modifications, have been used in preparation of new national probabilistic ground motion hazard maps by the U.S. Geological Survey. The five regions addressed are the Great Basin, the Northern Rocky Mountains, the Southern Rocky Mountains, the Central Interior, and the northeastern United States. Discussions at the workshops focussed on possible temporal and spatial variations of seismicity within the regions, latest ages of surface-fault displacements, most recent uplift or subsidence, geologic structural provinces as they relate to seismicity, and speculation on earthquake causes. Within the Great Basin region, the zones conform to areas characterized by a predominance of faults that have certain ages of latest surface displacements. In the Northern and Southern Rocky Mountain regions, zones primarily conform to distinctive structural terrane. In the Central Interior, primary emphasis was placed on an interpretation of the areal distribution of historic seismicity, although geophysical studies in the Reelfoot rift area provided data for defining zones in the New Madrid earthquake area. An interpretation of the historic seismicity also provided the basis for drawing the zones of the New England region. Estimates of earthquake maximum magnitudes and of recurrence times for these earthquakes are given for most of the zones and are based on either geologic data or opinion.

Circular↗
USGS1976

Fission-track ages of sphene and apatite of granitic rocks of the Salinian block, Coast Ranges, California

Fission-track ages have been determined on apatite and sphene from granitic rocks of the Salinian block, California Coast Ranges. The 26 age determinations on sphene range between 68 and 93 m.y. The 24 age determinations on apatite have a greater variation, ranging from 3 to 74 m.y. None of the fission-track ages appear to reflect times of intrusion. The Pinnacles volcanic field of Miocene age apparently has thermally affected apatite ages in the central Gabilan and eastern Santa Lucia Ranges. Reduced apatite ages in the area between the Farallon Islands and the Monterey Peninsula may also be the result of Miocene volcanic activity, but the evidence is less conclusive. Fission-track ages on sphene correlate closely with previously determined potassium-argon ages on hornblende and biotite but show an unexplained "bimodal" age distribution, the ages in the Gabilan and Santa Lucia Ranges being slightly, but consistently, lower (avg 75 m.y.) than the ages for terrane to the north and south (avg 85 m.y.) The overall pattern of the sphene and apatite fission-track ages, distinctly different from that of the central Sierra Nevada, may be a "fingerprint" of correlative value in locating the parent terrane of the "ripped-off" Salinian block.

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