Scientific teams analyze earthquake hazards of the cascadia subduction zone
[No abstract available]
Eos, Transactions, American Geophysical Union↗
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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.
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Conserving coastal wetlands despite sea-level rise
Abstract not supplied at this time
Eos, Transactions, American Geophysical Union↗
Imperfect science: Uncertainty, diversity, and experts
Seismic safety issues related to nuclear reactors in the eastern United States pose special challenges to the Earth and engineering sciences, given the severe consequences that can attend even very infrequent earthquakes. To deal with low-probability, potentially damaging ground motions, two major probabilistic seismic hazard analyses were conducted in the 1980s for nuclear reactors in the eastern United States, that part of the country east of the Rocky Mountains. The first study was performed by the Lawrence Livermore National Laboratory (LLNL) [ Bernreuter et al ., 1989] and was supported by the U.S. Nuclear Regulatory Commission (USNRC). The second was commissioned by the Seismicity Owners Group of the Electric Power Research Institute (EPRI) , [1989]. These studies generally agreed in terms of median hazard estimates, but mean hazard estimates at individual sites varied considerably, in several cases by 2 orders of magnitude or more.
Eos, Transactions, American Geophysical Union↗
Aftershocks: Are they earthquakes or afterthoughts?
We tend to view aftershocks as after-thoughts in their scientific as well as societal importance. The media often ask seismologists: “Was it just an aftershock?” with the “just” implying that aftershocks present little cause for concern. Seismologists themselves tend to dismiss the importance of events that follow a large mainshock. Even appreciable aftershocks typically generate only a fraction of the scientific interest and investigation that the mainshock does. However, consideration of recent earthquake sequences suggests that aftershocks can be even more damaging than mainshocks in some cases. That is, although the aftershocks are still, by definition, smaller events, they could be even more damaging by virtue of proximity to population centers or other circumstances.
Eos, Transactions, American Geophysical Union↗
Toward a comprehensive catalog of global historical seismicity
The United States Geological Survey (USGS) and the Colorado School of Mines (CSM) have initiated a project to locate more accurately all earthquakes recorded by instruments during the period 1900 to 1963. Seismicity for this period (hereafter referred to as historical seismicity, following Lee et al . [1988]) is still poorly understood, even for basic parameters such as earthquake locations (see Figure 1). In some cases this is the result of inherent limitations in the distribution, response characteristics, and timing of the instruments. However, locations for most of the pre-1964 earthquakes are poorly determined simply because modern data analysis techniques have yet to be applied to the available arrival-time observations, which are mainly preserved as printed bulletins and not in a computer-ready digital format. The arduous task of hand-entering these data has prevented the systematic analysis and relocation of historical seismicity.
Eos, Transactions, American Geophysical Union↗
Streams in Catskill Mountains still susceptible to acid rain
Precipitation in North America has become less acidic over the past 2 decades because of reduced power plant emissions and compliance with the Clean Air Act Amendments [ Sirois , 19937rsqb;. The 1990 Clean Air Act Amendments were developed to reduce the acidity of sensitive surface waters, which are primarily in upland forested environments, where acidified waters and associated high aluminum concentrations are toxic to many species of aquatic flora and fauna [ Schindler et al. , 1989]. Our studies show that in spite of less acidic precipitation, the buffering capacity of streams in upland forests of the Catskill Mountains in southeastern New York has not increased in recent years. These data suggest that long-term leaching by acid rain has lowered exchangeable calcium ion concentrations in the soil in upland areas, where the underlying, slow-weathering bedrock provides an inadequate supply of cations to neutralize acidity.
New York↗
Major improvements in progress for Southern California Earthquake Monitoring
Major improvements in seismic and strong-motion monitoring networks are being implemented in southern California to better meet the needs of emergency response personnel, structural engineers, and the research community in promoting earthquake hazard reduction. Known as the TriNet project, the improvements are being coordinated by the California Institute of Technology (Caltech), the U.S. Geological Survey (USGS), and the California Division of Mines and Geology (CDMG) of the state's Department of Conservation. Already the ambitious instrument and system development project has started to record and disseminate ground motions from a spatially dense and robust network of high quality seismographs.
Eos, Transactions, American Geophysical Union↗
[Book Review] The Dead Sea, the lake and its setting, edited by T. Niemi, Z. Ben-Avraham, J. Gat
Review of The Dead Sea, the Lake and its Setting. Tina M. Niemi, Zvi Ben-Avraham, and Joel R. Gat (Editors). Oxford Monographs on Geology and Geophysics No. 36. Oxford University Press, N.Y. 286 pp. ISBN 0-19-508703-8, 1997. $75.
Eos, Transactions, American Geophysical Union↗
Satellite radar interferometry measures deformation at Okmok Volcano
The center of the Okmok caldera in Alaska subsided 140 cm as a result of its February– April 1997 eruption, according to satellite data from ERS-1 and ERS-2 synthetic aperture radar (SAR) interferometry. The inferred deflationary source was located 2.7 km beneath the approximate center of the caldera using a point source deflation model. Researchers believe this source is a magma chamber about 5 km from the eruptive source vent. During the 3 years before the eruption, the center of the caldera uplifted by about 23 cm, which researchers believe was a pre-emptive inflation of the magma chamber. Scientists say such measurements demonstrate that radar interferometry is a promising spaceborne technique for monitoring remote volcanoes. Frequent, routine acquisition of images with SAR interferometry could make near realtime monitoring at such volcanoes the rule, aiding in eruption forecasting.
Eos, Transactions, American Geophysical Union↗
Seismic survey probes urban earthquake hazards in Pacific Northwest
A multidisciplinary seismic survey earlier this year in the Pacific Northwest is expected to reveal much new information about the earthquake threat to U.S. and Canadian urban areas there. A disastrous earthquake is a very real possibility in the region. The survey, known as the Seismic Hazards Investigation in Puget Sound (SHIPS), engendered close cooperation among geologists, biologists, environmental groups, and government agencies. It also succeeded in striking a fine balance between the need to prepare for a great earthquake and the requirement to protect a coveted marine environment while operating a large airgun array.
Washington↗
Debating complexity in modeling
Complexity in modeling would seem to be an issue of universal importance throughout the geosciences, perhaps throughout all science, if the debate last year among groundwater modelers is any indication. During the discussion the following questions and observations made up the heart of the debate. As scientists trying to understand the natural world, how should our effort be apportioned? We know that the natural world is characterized by complex and interrelated processes. Yet do we need to explicitly incorporate these intricacies to perform the tasks we are charged with? In this era of expanding computer power and development of sophisticated preprocessors and postprocessors, are bigger machines making better models? Put another way, do we understand the natural world better now with all these advancements in our simulation ability? Today the public's patience for long-term projects producing indeterminate results is wearing thin. This increases pressure on the investigator to use the appropriate technology efficiently. On the other hand, bringing scientific results into the legal arena opens up a new dimension to the issue: to the layperson, a tool that includes more of the complexity known to exist in the real world is expected to provide the more scientifically valid answer.
Eos, Transactions, American Geophysical Union↗
Airborne laser study quantifies El Niño-induced coastal change
Winter storms during the 1997–1998 El Niño caused extensive changes to the beaches and cliffs of the west coast of the United States, a NASA-NOAA-USGS investigation using a scanning airborne laser has found. For example, near Pacifica in central California, the cliff eroded locally as much as 10–13 m landward during the El Niño winter, at least 40 times the long term average erosion rate. However, only several hundred meters away the cliff was stable. This variability in cliff response may be related to differences in local beach changes where an accreting beach protected part of the cliff and an eroding beach exposed another part to attack by waves.
Pacific Coast↗
Water, population pressure, and ancient Indian migrations
A preliminary report on environmental factors relating to some prehistoric Indian migrations in the lower San Juan Valley region, northeastern Arizona
Arizona↗
The U.S. Geological Survey's gravity program in the Rocky Mountain and Basin Range areas
Most of the gravity surveys of the U.S. Geological Survey have been support programs in connection with regional geologic structural studies, ground-water investigations, and heavy-metals exploration. Many of the studies were undertaken in conjunction with geological mapping and mineral investigations by the Survey's project geologists. Gravity data often complement aeromagnetic surveys to identify the sources of potential-field anomalies; other gravity data have been used to supplement high-resolution seismic and electrical investigations [ Mattick , 1967]. Geochemical follow-up has been fruitful in western Montana [ Mudge et al, 1967].
Arizona, Colorado, Idaho, Montana, Nevada, New Mex↗
IASH Commission of Snow and Ice meeting: Paris, France, September 3-5, 1969
The IASH Commission of Snow and Ice met jointly with the Working Group on Glaciology of the Special Committee on Antarctic Research (SCAR). Five technical guides have been prepared by the Commission of Snow and Ice for major IHD projects and have been in press at Unesco for more than a year and a half. They should be published by December 1969. A sixth guide, on Sea, Lake and River Ice, was approved for publication, and two other guides (Avalanche Classification and Part 2 of Combined Heat, Ice, and Water Balances) have been distributed in first or second draft form. They should be ready for approval by the next meeting of the officers of the Commission. Even though these guides have not yet been officially published, they have served as instruction and coordination media for a large number of glacier and seasonal snow cover projects in many nations during the first part of the International Hydrological Decade.
Eos, Transactions, American Geophysical Union↗
A progress report: Water conservation by removal of phreatophytes
Evapotranspiration from the flood plain of a major river depletes the water contributed from upstream areas of the watershed. This depletion can be significant in arid regions where water supplies are inadequate. Phreatophyte control offers a method of reducing the evapotranspiration and thus increases the water available to downstream users. This control is achieved by removing the woody phreatophytes and replacing them with grasses having a lower consumptive use.
Arizona↗
International symposium on hydrometry
Approximately 520 engineers and scientists from 55 countries attended the International Symposium on Hydrometry held at Koblenz, Federal Republic of Germany, from September 13 through 22, 1970. The symposium was convened by Unesco and organized in cooperation with the World Meteorological Organizations (WMO), Unesco, the National Committee for the International Hydrological Decade of the Federal Republic of Germany, and the International Association of Scientific Hydrology (IASH). The symposium was organized within the framework of the International Hydrological Decade (IHD). After a welcoming speech by J. Wallner, Chairman of the Organizing Committee, the opening address was presented by S. Dumitrescu, the representative of Unesco. Introductory statements were then delivered by T. Palas, the representative of WMO; by L.J. Tison, the representative of IASH; and by K. Wittock, the representative of the Government of the Federal Republic of Germany.
Eos, Transactions, American Geophysical Union↗
Investigations at active volcanoes
The field of volcanology has expanded greatly in the years 1967–1970, and work on active volcanoes has kept pace with this expansion. I have restricted this summary and the accompanying bibliography to studies by U.S.‐based investigators of active or potentially active volcanoes. I have been immeasurably aided in writing this summary by communications from R. Citron of the Smithsonian Institution Center for Short‐Lived Phenomena, W. Melson and T. Simkin of the Smithsonian Institution, A. McBirney of the Center for Volcanology, University of Oregon, R.B. Forbes of the University of Alaska, and R.W. Decker of Dartmouth College.
Eos, Transactions, American Geophysical Union↗