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At least 91 records · Page 5Linked to original sources
USGS1991

The nature of earthquake prediction

Earthquake prediction is inherently statistical. Although some people continue to think of earthquake prediction as the specification of the time, place, and magnitude of a future earthquake, it has been clear for at least a decade that this is an unrealistic and unreasonable definition. the reality is that earthquake prediction starts from the long-term forecasts of place and magnitude, with very approximate time constraints, and progresses, at least in principle, to a gradual narrowing of the time window as data and understanding permit. Primitive long-term forecasts are clearly possible at this time on a few well-characterized fault systems. Tightly focuses monitoring experiments aimed at short-term prediction are already underway in Parkfield, California, and in the Tokai region in Japan; only time will tell how much progress will be possible.

Earthquakes & Volcanoes (USGS)↗
USGS1990

Volcanology and mineral deposits

Traditionally, volcanologists have focused on forecasting, observing, and interpreting events, processes, and products of eruptions at active volcanoes. Such work involves drama, beauty, fascination scientific problems, and the socially important aim of reducing risks to life and property. In contrast, old volcanic regions, which host many of the world's major hydrothermal-vein, porphyry, and massive-sulfide ore deposits, have been studied mainly by economic geologists, regional stratigraphers, and structural geologists who have limited familiarity with the complexities of volcanic processes. Such "dead" volcanoes, ranging in age from a few million million years (tertiary) to a few billion years (Precambrian), are commonly incompletely and discontinuously preserved due to rapid erosion of originally high-standing volcanic edifices. They can be difficult to date reliably, especially in terms of the time scales of individual volcanic events, and are variably hydrothermally altered-impeding high-resolution petrologic and geochemical studies. Many volcanologists, geochemists, and geophysicists who work on active volcanoes accordingly have been reluctant to become involved in studies of such less tractable rocks.

Earthquakes & Volcanoes (USGS)↗
USGS1987

Devastating tsunami inspires efforts to reduce future tsunami destruction

The beacon from landmark Scotch Cap lighthouse pierced the moonless night of April 1, 1946, in Alaska's remote Aleutain Island chain. In the reinforced concrete lighthouse, five men were engaged in various support operations connected with the maintenance of the 80,000 candlepower beam. Perched atop a building constructed 5 years earlier on a bluff 32 feet above sea level, the proud new light rose a total of 92 feet above the swirling restless seas. On a cliff behind the lighthouse, a second building housed the Coast Guard radio-direction-finding station.

Alaska↗
USGS1988

Volcanoes can generate devastating waves

Explosions. Noxious gases. Lava fountains and flows. Avalanches of superheated pyroclastics. Although volcanic eruptions can cause all these frightening phenomena, it is often the power of the sea that causes many volcano-related deaths. this destruction comes from tsunamis (huge volcano-generated waves) Roughly one-fourth of the deaths occurring during volcanic eruptions have been the result of tsunamis. Moreover a tsunami can transmit the volcano's energy to areas well outside the reach of the eruption itself.

Earthquakes & Volcanoes (USGS)↗
USGS1989

NEIC; the National Earthquake Information Center

Mexico was hit by one of the most devastating earthquakes in its history on September 19, 1985 at 7:18 a.m. MDT time. this earthquake, which was centered about 380 kilometers west-southwest of Mexico City, had a surface-wave magnitude of 8.1. In less than a minute, seismic waves from this earthquake had traveled to Mexico City. At this early hour, people were beginning to get ready for the day's work. Without warning, buildings in some sections of the city began to shake violently. A few minutes later, 412 buildings had collapsed and another 3,124 were badly damaged (figure 1). Most communication systems linking Mexico City to the rest of the world were damaged or rendered inoperable. At least 9,500 people were killed, 30,000 were injured and 100,000 were left homeless by this earthquake. According to some unconfirmed reports, the death toll from this earthquake may have been as high as 35,000. this earthquake is estimated to have seriously affected an area of 825,000 square kilometers, caused between 3 and 4 billion dollars in damage, and been felt by 20 million people.

Earthquakes & Volcanoes (USGS)↗
USGS1992

Correlation between atmospheric precipitation and recent explosions at Mount St. Helens, Washington

Scientists attribute the recent small explosion-like seismic signals at Mount St. Helens to either the geyser-like flashing of superheated groundwater to steam or the release of magmatic gas from the cooling magma system, or both. The contribution of magmaic gas in these events is not currently known. If meteoric water from rain or melting snow is the source, however, we might expect these events to occur most frequently during the rainy season, perhaps even during or immediately following individual storms.

Washington↗
USGS1987

Picture windows of opportunity

We hate to say that we need a moderate earthquake every once in a while, but experience shows that it surely helps to sell all kinds of seismic safety programs It took the 933 Long Beach earthquake to get the Field Act passed in California requiring the strengthening of our public schools. It took the 197 San Fernando earthquake for Los Angeles to enact a retrofit ordinance requiring reinforcement of demolition of our 8,000 unreinforced masonry buildings, and the 1985 Mexico City earthquake to shorten its compliance period. It took the 1983 Coalinga earthquake to get the State of California to require the identification of unreinforced masonry buildings in risk areas throughout the state.

Earthquakes & Volcanoes (USGS)↗
USGS1993

Where lava meets the sea; Kilauea Volcano, Hawaii

Active volcanoes on the island of Hawai'i provide scientists with exceptional opportunities to observe volcanic phenomena at close range. Such an opportunity occurred on November 24, 1992, when geologists from the Hawaiian Volcano Observatory (HVO) witnessed spectacular explosive interactions between lava and seawater on the southeast coast of the island. As seawater invaded submarine conduits transporting milten lava, large steam explosions produced glowing fountains of lava that rose as high as 100m into the air and built a 7.5-m-high mound of volcanic ejecta called a littoral cone (see cover paragraphs). Seaside explosions of the type and magnitude of the event on November 24, 1992, are infrequent. the observation of this event represents a rare opportunity to enhance our understanding of the birth of littoral cones and the nature of explosive activity when lava enters the ocean.

Hawaii↗
USGS1992

Preliminary seismological results

On April 25 and April 26, 992, three earthquakes with magnitude (M) equal to or greater than 6.6 occurred near Cape Mendocino, California. the sequence began with a relatively shallow earthquake (M=7.1) on Saturday, April 25, at 11:06 a.m. local time. The two most most powerful aftershocks has magnitudes of 6.6 and 6.7. They occurred at 00:41 a.m. and 4:18 a.m. local times, respectively, on Sunday, April 26. The mainshock had a focal depth of about 10 km and the hypocenters of the strong afterschokcs were about 20 km deep. During the next three weeks, approximately 1500 aftershocks were recorded by the seismographic networks of the U.S Geological Survey. Some 200 of these events had M ≥3.0.

California↗
USGS1990

Communicating risk information and warnings

Major advances have occurred over the last 20 years about how to effectively communicate risk information and warnings to the public. These lessons have been hard won. Knowledge has mounted on the finding from social scientific studies of risk communication failures, successes and those which fell somewhere in between. Moreover, the last 2 decades have borne witness to the brith, cultivation, and blossoming of information sharing between those physical scientists who discover new information about risk and those communcation scientists who trace its diffusion and then measure pbulic reaction.

Earthquakes & Volcanoes (USGS)↗
USGS1987

Three volcanoes erupt in Alaska

Alaska has over 40 historically active volcanoes and normally averages one eruption a year. Alaskan volcanoes were unusually active in 1986. Augustine, Pavlof, and Akutan volcaneos all erupted vigorously; at one time in April, all three were erupting.

Alaska↗
USGS1988

Otto W. Nuttli; a memorial

With the death of Otto W. Nuttli from cancer on February 9, 1988, the Seismological Society of America lsot one of its most respected and beloved members.

Earthquakes & Volcanoes (USGS)↗
USGS1991

Mid-continent earthquake zones; lessons from New Madrid, Missouri

Many seismically active regions occur throughout the world as concentrated zones surrounded by the relatively stable crust of shields or platforms. Examples occur in central and eastern North America, northeastern Brazil, Australia, Norway, Svalbard, Greenland, and other places. Some of these zones, such as those at New Madrid, Missouri, and in the St. Lawrence Valley on the Canadian border, extend over relatively large areas and are marked by a high level of seismicity. Others, such as that near Anna Ohio, are smaller, and the level of activity is lower. Some zones are occasinoally sites for major earthquakes which, if they are in populated regions, can cause widespread destrucion and loss of life.

Missouri↗
USGS1992

Small explosions interrupt 3-year quiescence at Mount St. Helens, Washington

On December 11, 1989, geologists working in the crater at Mount St. Helens discovered two thin layers of ash separated by fresh snow-clear evidence that at least two small explosions had occurred recently. The explosions were neither seen nor heard, but on December 7 scientists suspected that a small ash-producing explosion had occurred when seismometers near the volcano recorded a long explosion-like signal, and titlt and displacement meters showed minor deformation of the dome. There were no other large seismic signals to account for the second ash layer, which was most likely associated with one of several smaller signals in early December. The December ash-producing explosions were the first eruptive activity at Mount St. Helens since October 1986. There have been at least five more ash-producing explosions since December 1989, all without recognized seismic or other geophysical precursors. The ash from these explosions appears to be pulverized pieces of dacite dome. The absence of glass shards in the ash suggests that no new magmatic material was ejected. Several of the explosions were accompanied by snow and rock avalanches, pyroclastic flows, ballistic showers, and debris flows. These ash-producing explosions are part of a series of at least 28 explosion-like seismic events that began on August 24, 989. Seismic signals from these events resemble those associated with confirmed ash-producing explosions in April-May 1986. Yet not all of the 1989-1991 events produced ash plumes. Excellent visual observations during four of the events indicated that neither a steam nor ash plume was generated. There is little information about the other events because they occurred when the mountain was not visible, nor was there physical evidence of ashfall or surface changes when scientists visited the crater days to weeks alter. Considerable deformation of the north side of the dome occurred during the series of explosion-like seismic events. Sections of the dome slumped northward and two new vents were formed. However, monitoring the changes associated with individual events was often impossible because several key electronic-distance-meter (EDM) targets and tiltmeters were destroyed by the series of events.

Washington↗
USGS1991

Don’t fence us in

When I was a graduate student around 1950 I used to read the entire Bulletin of the Seismological Society of America. it was a pwoerful and inspiring educational experience, with an effect quite different from that of the more usual process of looking up a few articles in the chain of references in a subject of current interest. Reading the entire journal reveals how ideas, techniques, and seismologists appear and evolve. It is likely the best substitute for a firsthand personal experience with the early development of the field. And in spite of, or perhaps because of, the missteps, the wasted effort, and the lack of sophistication that those first volumes reveal, the reader can sense the opportunity and be inspired by the vibrancy of the young subject.

Earthquakes & Volcanoes (USGS)↗