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The April 25-26, 1992, earthquakes caused significant changes in the landscape of the Cape Mendocino region. Although fault rupture did not break through to the surface, effects on the landscape included landslides, ground cracking due to strong shaking, liquefaction features (described later in this article), and uplift along the coast. The location map on the next page shows the distribution of some of these features.
Natural disasters affect countires large and small, rich or poor, whatever their political persuasion. The toll exacted by natural calamities each year drains the human and economic resources of every nation and stands as one of the formidable barriers to national, regional, and world development. Over the last 20 years, natural disasters have killed nearly 3 million people and disrupted the lives of over 800 million others. In 2 years there were more than 50 serious natural disasters, including landslides in Italy, France, and Colombia; a typhoon in Korea; wildfires in China and the United State; a windstorm in England; grasshopper plagues in Africa's horns and the Sahel; tornadoes in Canada; devastating earthquakes in Soviet Armenia and Tadzhikistan; infestations in Africa; landslides in Brazil; and tornadoes in the United States.
Earthquakes & Volcanoes has achieved much in its 20-year history. It serves as a link with policy makers and the public. it offers a variety of information attractive to professionals: historical, culutral, and curent events, and news items not found or missed elsewhere. And the journal can anticipate an even mroe important role in the future because, with increasing concentrations of population as well as building costs, people and their constructs have become mroe vulnerable to hazards.
Tokyo, Japan's capital, has been enjoying a seismically quiet period following the 1923 Kanto earthquake of magnitude 7.9 that killed more than 140,000 people. Such a quiet period seems likely to be a repetition of the 80-year quiescence after the great 1703 Genroku earthquake of magntidue 8.2 that occurred in an epicentral area adjacent to that of the 1923 Kanto earthquake. In 1784, seismic activity immediately under the capital area revived with occasional occurrence of magnitude 6 to 7 shocks. Earthquakes of this class tended to occur more frequently as time went on and they eventually culminated in the 1923 Kanto earthquake. As more than 60 years have passed since the Kanto earthquake, we may well expect another revival of activity immediately under the capital area.
The principal hazards from earthquakes are surface faulting, ground failure, and ground shaking. In coastal areas tsunamis, or seismic sea waves, also are a potential hazard. We will consider each of these hazards briefly to assess their possible effects on the structures of man.
Past investigations by myself and others on the role of the mass media in disasters indicate that news people typically find themselves in situations of uncertainty, ambiguity, and conflicting information; the communication and transportation services that these people use in covering a story become inoperative. However, the media are expected to make sense of the disaster situation almost immediately. the difficulties of doing so were reflected by the ABC Goodyear Blimp footage of the collapsed Nimitz Freeway in Oakland, California, broadcast nationally on the evening of October 17, 1989. The televised picture showed the disastrous results of the Loma Prieta earthquake, but for an hour or more the announcer could not correctly identify what was being shown. He did not seem to realize that the upper deck of the freeway had collapsed on the lower deck, crushing vechiles and people.
Trenching studies of the San Andreas fault have been of great value to geologists in California for determining not only the prehistoric occurrences of earthquakes on the fault bu also the age of these movements. In the New Madrid seismic zone, U.S Geological Survey scientists have been trenching across suspected faults to try to assess earthquake frequency in the Central U.S. The following photographs document these trenching studies.
Cooperative research by scientists of the United States and the People's Republic of China (PRC) has resulted in important new finding concerning the fundamental characteristics of earthquakes and new insight into mitigating earthquake hazards. Much of the research is being conducted under the U.S State Department Protocol for Scientific and Technical Cooperation in Earthquake Studies between the PRC State Seismological Bureau (SSB) and the U.S Geological Survey and the National Science Foundation. Activites and prgoress accomplished under the protocol were the subject of two special sessions at the 1985 American Geophyiscal Union Fall Meeting in San Francisco, Calif.
Faulting associated with the June 28, 992, earthquake near Landers, California, broke the surface of the ground over a length of more than 70 km, the longest surface rupture in the United States since the great San Francisco quake of 1906. the strongest shaking associated with this magnitude 7.6 (M S ) earthquake, the largest in the contiguous 48 states in the last 40 years, occurred in a sparsely populated sections of the Mojave Desert more than 200 km east of Los Angeles. the earthquake began with a sudden slip on the Johnson Valley fault about 10 km southwest of Landers. The initial fault movement probably occurred at a depth of less than 10 km. Surface faulting then propagated over 70 km to the north and northeast. The faulting linked preexisting faults-some previously known and mapped and others previously unknown-into a complex, coherent rupture zone.
Data from the past 20 years indicate a strong temporal correlation between major California earthquakes and icnreased federal funding for seismology.
The Salton Sea Scientific Drilling Program (SSSDP) was the first large-scale drilling project undertaken by the U.S Continental Scientific Drilling Program. The objectives of the SSSDP were (1) to drill a deep well into the Salton Sea Geothermal Field in the Imperial Valley of California, (2) to retrieve a high percentage of core and cuttings along the entire depth of the well, (3) to obtain a comprehensive suite of geophysical logs, (4) to conduct flow tests at two depths (and to take fluid samples therefrom), and (5) to carry out several downhole experiments. These activites enabled the U.S Geological Survey and cooperating agencies to study the physical and chemical processes involved in an active hydrothermal system driven by a molten-rock heat source. This program, orginally conceived by Wilfred A. Elders, professor of geology at the University of California at Riverside, was coordinated under an inter-agency accord among the Geological Survey, the U.S Department of Energy, and the National Science Foundation.
Advances in science are memorialized; diversion are soon forgotten. Yet it is a diversion that I commemorate here: the v p /v s anomaly, the so-called seismic velocity ratio, as a method of predicting the time, place, and magnitude of an impending earthquake.
There was no warning. The British Airqays Boeing 747 was making its usual flight from Kuala Lumpur to Perth, Asutralia, that nihgt, late in June 1982. Altitude:12,000 metres (37,000 feet). Time about 23:00 UTC. Suddenly, an acrid odour began to pervade the aircraft, an eerie bluish glow lit up the edges of the wings, and in the cockpit the familiar hum of static started to break up the high-frequency communications. Then it happened.
Few studies have attempted to describe the large numbers of medals that have been struck to commemorate important seismological events. I was intrigued by these medals on the occasion of the transfer of the coin and medal collection from the Freiberg Military Academy to the special reserve of the University of Dresden. Seismic events are environmental events, so it is not surprising that mankind, in coming to terms with earthquakes, has tried to express his feelings about them in an artistic manner too. By understanding the topical importance of medals in seismological affairs, we can appreciate the hertiage of the past.
Earthquakes have been occurring in California for eons and will continue to play an important role in the evolution of California landforms. Recent California earthquakes have been of moderate size (magnitude 5.5 to less than 7), have occurred in rural or low population areas, and have therefore been important mainly to scientists and local citizens. Nevertheless, because of the loss that can result from ground shaking during an earthquake, experiments are now being planned for the Parkfield area that will improve the prediction to ground motion and the understanding of damage to small structures and pipelines.
Earthquakes have rocked the Klamath Falls in the past will continue to do so in the future. Scientists estimate the likelihood of future damaging earthquakes in an area by examining the area's past record of earthquakes and by evaluating the area's earthquake potential in relationship to its geologic setting. To supplement the historic catalog, which often covers only a short time span, they also attempt to identify prehistoric earthquakes preserved in the rocks and sediments of the area. The conclusion drawn from such studies in the Klamath Falls area is that earthquakes in the 4-6 magnitude range, which are capable of light to moderate damage, occur on the order of one or more every few decades. Even a major earthquake in the 7+ magnitude range cannot be ruled out at some future time. However, the area's historic record, which goes back only about 100 yrs, is too short to estimate the frequency of such large shocks. This article is a brief summary of the geologic setting and the historic and prehistoric record of earthquakes in Klamath Falls and the surrounding area.
Ever since 1935, when C.F Richter devised the earthquake magnitude scale that bears his name, seismologists have been able to view energy release from earthquakes in a systematic and quantitative manner. The benefits have been obvious in terms of assessing seismic gaps and the spatial and temporal trends of earthquake energy release. A similar quantitative treatment of volcanic activity is of course equally desirable, both for gaining a further understanding of the physical principles of volcanic eruptions and for volcanic-hazard assessment. A systematic volcanologic data base would be of great value in evaluating such features as volcanic gaps, and regional and temporal trends in energy release.
In late 1985 and early 1986 a comet was visible to the Earth that has been observed for over 2000 years. One of the most famous of celestial visitors, Comet Halley appeared last in 1910 and will not be seen again until the year 2061. the comet has been the focus of intense studies during the International Halley Watch. A fleet of Soviet, Japanese and European spacecraft was launched specifically for a direct encounter with the comet in March of this year; numerous ground-based astronomical observations are being made, while other investigations are being made from Earth-, Venus- and interplanetary-orbits. In short, Comet Halley will have been one of the most significant scientific occasions of the decade. In 1705 Edmund Halley, Professor of Geometry at Oxford University, collected and organized a mass of information on comets observed in 1531, 1607, and 1682, a task for which he had an uncommon genius. He was able to show that the comets had very similar orbits, and correctly drew the conclusion that they were the same object and more importantly that comets could therefore be periodic. He predicted that this comet would again be visible from the Earth in 1759. Since then it has been known as Halley's comet and it has played a significant role in the development of astronomy.