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New Publication Sheds Light on Earthquake Hazards in the San Francisco Bay Region
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![[alt text]](velocity-structure.jpg)
Under San Francisco Bay: This illustration from the cover of Professional Paper 1658 shows the upper-crustal seismic-velocity structure of the San Francisco Bay region, as determined from analysis of seismic waves generated by local earthquakes and controlled sources. Warm colors (yellow, orange) indicate slower velocities, cool colors (green, blue, purple) indicate faster velocities. (Differences in seismic velocity typically indicate differences in rock type.) Red lines denote surface fault traces. Lateral changes in seismic velocity correlate with faults at depth and result from rock units of different lithologies being offset by faults. Yellow spheres show locations of some of the earthquake hypocenters used in analysis. View southeastward from near San Francisco.
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A new publication from the U.S. Geological Survey (USGS) presents research findings about crustal structure, the locations of earthquake faults, and liquefaction processes in the San Francisco Bay region. Entitled "Crustal Structure of the Coastal and Marine San Francisco Bay Region, California," USGS Professional Paper 1658 is a compilation of eight chapters by a total of 26 authors, with 145 pages and two large maps.
Part of the introduction is quoted here:
"The San Francisco Bay region is home to about 7 million people, ranking fifth among population centers in the United States. Most of these people live on the coastal lands along San Francisco Bay, the Sacramento River delta, and the Pacific coast. The region straddles the tectonic boundary between the Pacific and North American Plates and is crossed by several strands of the San Andreas Fault system. These faults, which are stressed by about 4 cm of relative plate motion each year, pose an obvious seismic hazard.
"We have many ways to study earthquake faults. Where faults break the land surface, we may learn valuable information needed for hazard assessment, such as cumulative offset, slip rate, and earthquake history. However, many of the major faults in the region are partly submerged beneath San Francisco and Monterey Bays. Although this situation poses problems in gathering observational data for hazard assessment, bay-region waterways provide an opportunity to study fault-zone structure by using marine subsurface-imaging techniques, which are easier and cheaper than equivalent studies on land.
"In 1993, the [USGS] launched a 5-year project aimed at unearthing the basic science of the submerged San Andreas strike-slip fault system in the San Francisco Bay region with its many interacting strands. Primary project goals were structural, such as to discover how the San Andreas and Hayward Faults are connected or related at depth, to learn how the complex of faults in the San Andreas stepover zone on the Golden Gate platform functions, and to locate previously unknown faults. This volume thus contains mostly structural information about the San Francisco Bay region, much of it gathered through exploratory geophysical experiments."
The volume presents a wealth of information derived from various sources, including earthquake tomography, seismic-reflection data, aeromagnetic data, ground-penetrating-radar tomography, microfossil analysis, and study of the historical record of a small tsunami generated by the great 1906 San Francisco earthquake.
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Feb. / Mar. 2003
in this issue:
cover story:
Competitive Edge of Invasive Species
Lake Mead Work Continues
Dolphin Rescue
London Interns Tour St. Pete
Congressional Briefing on Gas Hydrates
Volcanic Ash and Aviation Safety
Science Mentoring
Coastal Vulnerability
Lidar Data and Technology
International Deep-Sea Corals Workshop
Northeastern Coastal Ecosystems and Resources Workshop
Shinn Wins 2002 Shoemaker Distinguished Achievement Award
Coastal and Marine Scientists Win 2002 Shoemaker Product Excellence Awards
Behrendt and Poag Elected AAAS Fellows
Normark Awarded Keen Medal
A Tribute to Joe Newell
Marine Geophysics Pioneer Honored
Celebrating Careers of Five Retirees
Manheim Lectures on Trends in Scientific and Technological Innovation
San Francisco Bay Earthquake Hazards
Effectivenes of Marine Reserves in Central California
Human Influence on Diatom Productivity and Sedimentation in Chesapeake Bay
Feb. / Mar. Publications List
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U. S. Department of the Interior | U.S. Geological Survey
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