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Results for “Geological Society of America Memorials”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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3 recordsLinked to original sources
USGS2016

Memorial to Robert Leland Smith 1920-2016

Robert L. Smith, renowned volcanologist and distinguished scientist with the U.S. Geological Survey (USGS), was a world authority on ash-flow tuffs, silicic volcanism, and caldera structures. Bob died peacefully in Sacramento, California, June 17, 2016, a few days short of his ninety-sixth birthday. His publications on ash flows and their deposits brought about an international revolution in understanding of explosive silicic volcanism and, in his fifty-year career, he profoundly influenced USGS programs and countless scientists.

Geological Society of America Memorials↗
USGS2020

Memorial to Jack B. Epstein 1935-2020

Jack Burton Epstein, a career geologist with the U.S. Geological Survey (USGS) passed away in May 2020 at his home in Great Falls, Virginia. His career and contributions to the USGS spanned more than 60 years from his time as a summer field assistant while attending college, through 40 years as a research geologist, and more than 15 years as an emeritus scientist. Jack was born December 27, 1935 in Brooklyn, New York and attended CUNY- Brooklyn College where he received his Bachelor of Science degree in geology in 1956. He earned his Master of Science degree in 1958 from the University of Wyoming, and his doctorate degree in geology in 1970 from The Ohio State University. His master’s thesis was geologic mapping of the Fanny Peak quadrangle, Black Hills of Wyoming and South Dakota, and his Ph. D. dissertation focused on the geology of the Stroudsburg quadrangle and adjacent areas, Pennsylvania and New Jersey.

Geological Society of America Memorials↗
USGS2006

Modeling and validation of a 3D velocity structure for the Santa Clara Valley, California, for seismic-wave simulations

A 3D seismic velocity and attenuation model is developed for Santa Clara Valley, California, and its surrounding uplands to predict ground motions from scenario earthquakes. The model is developed using a variety of geologic and geophysical data. Our starting point is a 3D geologic model developed primarily from geologic mapping and gravity and magnetic surveys. An initial velocity model is constructed by using seismic velocities from boreholes, reflection/refraction lines, and spatial autocorrelation microtremor surveys. This model is further refined and the seismic attenuation is estimated through waveform modeling of weak motions from small local events and strong-ground motion from the 1989 Loma Prieta earthquake. Waveforms are calculated to an upper frequency of 1 Hz using a parallelized finite-difference code that utilizes two regions with a factor of 3 difference in grid spacing to reduce memory requirements. Cenozoic basins trap and strongly amplify ground motions. This effect is particularly strong in the Evergreen Basin on the northeastern side of the Santa Clara Valley, where the steeply dipping Silver Creek fault forms the southwestern boundary of the basin. In comparison, the Cupertino Basin on the southwestern side of the valley has a more moderate response, which is attributed to a greater age and velocity of the Cenozoic fill. Surface waves play a major role in the ground motion of sedimentary basins, and they are seen to strongly develop along the western margins of the Santa Clara Valley for our simulation of the Loma Prieta earthquake.

California↗