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William F. Isherwood

Publications and source records attributed to William F. Isherwood.

5 recordsLinked to original sources
USGS1978

Principal facts for gravity observations in the Coso Hot Springs area, California

Gravity observations were made at 292 locations in the Coso Hot Springs area, California (figs. 1 and 2). The field work was completed during June 1976 by William F. Isherwood and Jerry H. Hassemer using LaCoste-Romberg Gravity Meters G-131 and G-159. The purpose of the gravity survey is to provide background geophysical data to evaluate the geothermal potential of the area. The present survey fills in gaps of coverage on previous gravity maps of the region (Nilsen and Chapman, 1971, and Chapman and others, 1971).

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USGS1976

Gravity and magnetic studies of the Geysers-Clear Lake geothermal region, California, USA

Gravity and magnetic fields in The Geysers-Clear Lake region are interpreted in relation to the known geology and other available geophysical data. New gravity data provide additional detail with the area of geothermal steam production. Computer techniques were used for removal of the regional gravity field, anomaly enhancement, and modeling subsurface structures. The gravity field was separated into three components: (1) a regional field presumed to be due to deep crustal structure related to the continental margin; (2) a residual gravity low of approximately 30 mgal centered over Mount Hannah and having an approximate diameter of 20 km, which is caused, according to our model, by a magma chamber whose top lies within 10 km of the surface; and (3) a closed residual low over the original steam production field. This low is probably related to effects within 1.5 km of the surface and was modeled as a steam-saturated reservoir structure. Local magnetic highs correlate with surface outcrops of serpentinite and relief on the volcanic rocks. Upward continuation of the aeromagnetic data suggests that the serpentinite body along the Collayomi fault may extend to a depth of more than 3 km near Boggs Mountain, but that other serpentinite bodies are probably more shallow. A long-wavelength magnetic high (centered at ~39°03'N 122°33'W) and a magnetic low (centered at ~38&deg:43'N 122°47'W) give half-width depth estimates of about 10 km. The center of the Mount Hannah gravity low lies in an area between these features and appears devoid of deep magnetic expression.

California↗
USGS1975

Gravity and magnetic studies of The Geysers-Clear Lake geothermal region, California

In order to explore for economic steam reservoirs, it is important to know the complete, three-dimensional geology which governs such a system. The Geysers-Clear Lake region California (figure 1), has the world's largest production of commercial power from a dry steam geothermal reservoir. This paper describes gravity and magnetic field analysis at The Geysers which defines a possible deep geologic structure and heat source.

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