USGS Science⌕ Search

Geology topics

D. H. Oppenheimer

Publications and source records attributed to D. H. Oppenheimer.

14 recordsLinked to original sources
USGS2011

A Geo-referenced 3D model of the Juan de Fuca Slab and associated seismicity

We present a Geographic Information System (GIS) of a new 3-dimensional (3D) model of the subducted Juan de Fuca Plate beneath western North America and associated seismicity of the Cascadia subduction system. The geo-referenced 3D model was constructed from weighted control points that integrate depth information from hypocenter locations and regional seismic velocity studies. We used the 3D model to differentiate earthquakes that occur above the Juan de Fuca Plate surface from earthquakes that occur below the plate surface. This GIS project of the Cascadia subduction system supersedes the one previously published by McCrory and others (2006). Our new slab model updates the model with new constraints. The most significant updates to the model include: (1) weighted control points to incorporate spatial uncertainty, (2) an additional gridded slab surface based on the Generic Mapping Tools (GMT) Surface program which constructs surfaces based on splines in tension (see expanded description below), (3) double-differenced hypocenter locations in northern California to better constrain slab location there, and (4) revised slab shape based on new hypocenter profiles that incorporate routine depth uncertainties as well as data from new seismic-reflection and seismic-refraction studies. We also provide a 3D fly-through animation of the model for use as a visualization tool.

British Columbia, California, Oregon, Washington↗
USGS2005

The seismic project of the National Tsunami Hazard Mitigation Program

In 1997, the Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS), and the five western States of Alaska, California, Hawaii, Oregon, and Washington joined in a partnership called the National Tsunami Hazard Mitigation Program (NTHMP) to enhance the quality and quantity of seismic data provided to the NOAA tsunami warning centers in Alaska and Hawaii. The NTHMP funded a seismic project that now provides the warning centers with real-time seismic data over dedicated communication links and the Internet from regional seismic networks monitoring earthquakes in the five western states, the U.S. National Seismic Network in Colorado, and from domestic and global seismic stations operated by other agencies. The goal of the project is to reduce the time needed to issue a tsunami warning by providing the warning centers with high-dynamic range, broadband waveforms in near real time. An additional goal is to reduce the likelihood of issuing false tsunami warnings by rapidly providing to the warning centers parametric information on earthquakes that could indicate their tsunamigenic potential, such as hypocenters, magnitudes, moment tensors, and shake distribution maps. New or upgraded field instrumentation was installed over a 5-year period at 53 seismic stations in the five western states. Data from these instruments has been integrated into the seismic network utilizing Earthworm software. This network has significantly reduced the time needed to respond to teleseismic and regional earthquakes. Notably, the West Coast/Alaska Tsunami Warning Center responded to the 28 February 2001 Mw 6.8 Nisqually earthquake beneath Olympia, Washington within 2 minutes compared to an average response time of over 10 minutes for the previous 18 years. ?? Springer 2005.

Natural Hazards↗
USGS2004

Remotely triggered seismicity on the United States west coast following the Mw 7.9 Denali fault earthquake

The M w 7.9 Denali fault earthquake in central Alaska of 3 November 2002 triggered earthquakes across western North America at epicentral distances of up to at least 3660 km. We describe the spatial and temporal development of triggered activity in California and the Pacific Northwest, focusing on Mount Rainier, the Geysers geothermal field, the Long Valley caldera, and the Coso geothermal field. The onset of triggered seismicity at each of these areas began during the Love and Raleigh waves of the M w 7.9 wave train, which had dominant periods of 15 to 40 sec, indicating that earthquakes were triggered locally by dynamic stress changes due to low-frequency surface wave arrivals. Swarms during the wave train continued for ∼4 min (Mount Rainier) to ∼40 min (the Geysers) after the surface wave arrivals and were characterized by spasmodic bursts of small ( M ≤ 2.5) earthquakes. Dynamic stresses within the surface wave train at the time of the first triggered earthquakes ranged from 0.01 MPa (Coso) to 0.09 MPa (Mount Rainier). In addition to the swarms that began during the surface wave arrivals, Long Valley caldera and Mount Rainier experienced unusually large seismic swarms hours to days after the Denali fault earthquake. These swarms seem to represent a delayed response to the Denali fault earthquake. The occurrence of spatially and temporally distinct swarms of triggered seismicity at the same site suggests that earthquakes may be triggered by more than one physical process.

North America↗
USGS2002

Comments on potential geologic and seismic hazards affecting Mare Island, Solano County, California

This report was prepared in response to a written request from the City of Vallejo, California, to the U.S. Geological Survey (USGS). By letter of October 4, 2002, the City requested that the USGS "provide advice to the City’s LNG Health and Safety Committee on its review of a potential liquid natural gas project" on the southern portion of Mare Island. The City specifically requested that the USGS advise the committee on potential hazards including fault rupture, earthquake ground motion, soil failure during earthquakes, tsunami and seiche, and landslides. The City requested that the USGS: (1) comment on these hazards, (2) describe its degree of confidence in its opinions, and (3) describe the scope of additional studies that will be needed if the City enters into an agreement with project sponsors. Advice was also requested on the selection of the safe shutdown and operating basis earthquakes as specified in the NFPA 59A standard (NFPA, 2001). This review of published reports and other publicly available information indicates that all of the hazards on which the USGS was asked to comment should be considered for the proposed project on the southern portion of Mare Island. Available information differs greatly for each of these potential hazards, and adequate understanding for design will require detailed site-specific investigations.

California↗
USGS1994

Earthquakes in California and Nevada

Each year seismic networks record more than 30,000 earthquakes with magnitudes (M) as small as 1.0 in California and Nevada. Historic accounts indicate more than 360 earthquakes of M ≥5.5 have occurred in this region between 1836 and 1994. This map depicts the recent and historic seismicity in three ways. The small red dots represent epicenters of earthquakes between 1 January 1980 and 31 January 1994. The black circles depict all known epicenters of M≥5.5 earthquakes since 1836. A number adjacent to an epicenter location refers to an entry in the table "Known M≥6.5 Earthquakes since 1836." The hachured regions indicate the surface projection of fault rupture for significant earthquakes as inferred from geologic observations of surface deformation and estimates of subsurface faulting from geophysical methods. Tightly spaced hachures represent vertical, strike-slip faults, and wider spaced hachures designate slipping faults.

California, Nevada↗
USGS1979

Abnormal P-wave delays in The Geysers-Clear Lake Geothermal area, California

Large teleseismic delays, exceeding 1 second, are found near Mount Hannah in the Clear Lake volcanic field and in the steam-production area at The Geysers. The delays are superimposed on a general delay field of about 0.5 second extending over the volcanic rocks and the steam reservoir. It is postulated that a magma chamber under the surface volcanic rocks with a core of severely molten rock beneath Mount Hannah and a highly fractured steam reservoir probably underlain by partially molten rock at The Geysers are responsible for the observed delays. Both zones extend to depths of 20 kilometers or more.

California↗