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At least 343 records · Page 19Linked to original sources
USGS1971

Results from the apollo-12 passive seismic experiment

The objective of the passive seismic experiment is to measure vibrations of the lunar surface produced by all natural and artificial sources of seismic energy and to use these data to deduce the internal structure and composition of the moon, the nature of forces which may cause deformation of the moon and moonquakes, and the numbers and masses of meteoroids striking the lunar surface. The ALSEP* seismometers can magnify lunar surface vibrations 10 million times. No instrument can operate on earth with this sensitivity, because weather and man produce too much seismic noise. To obtain answers to the above questions, seismic data must be combined with data from laboratory measurements of the physical and chemical properties of surface rocks, and many other geophyiscal and geochemical measurements. Thus far, we have had the opportunity to record data from two lunar seismic stations which were installed by the astronauts during Apollo misions and 12. The combined recording time from the stations is presently over 12 months, but there was no overlap to permit recording of the same event at two stations.

Earthquake Information Bulletin (USGS)↗
USGS1978

Water-level monitoring in the area of the Palmdale Uplift, Southern California

Abnormal behavior of water levels in wells has been observed prior to a number of earthquakes. For instance, water-level minima have been noted in the Cienega Winery well before earthquakes on the San Andreas fault. Abnormal water-level fluctuations were used in conjunctions with other precursors to predict the February 4, 1975, Haicheng earthquake in northeastern China. That such changes should occur prior to earthquakes is not surprising. Ground water that occupies the void spaces in porous rocks or alluvium can be expected to rise in wells when an aquifer is squeezed and fall when it is distended. COnfined aquifers, in particualr, have been found to be highly sensitive to Earth strain changes.

California↗
USGS1981

Two examples of seismic zonation in the San Francisco Bay region

The science of earthquakes in complex, requiring data and research in seismology, geology, soil mechanics, geophysics, hydrology, and engineering. Nevertheless, if earthquake hazards are to be reduced, earth science information must be translated from scientific and technical language into a form that can be effectively used by planners and decisionmakers. Out of the need to use earth science information in local and regional planning and decisionmaking came an experimental program-the San Francisco Bay Region Environment and Resources Planning Study. the study, begun in 1970, was jointly supported by the U.S Geological Survey and the U.S Department of Housing and Urban Development. The Association of Bay Area Governments and the planning firm of William Spangle and Associates, Inc., participated in the study and provided a liaison and communication link with other regional agencies and with local governments. Since 1975, the composition of the core group within the U.S Geological Survey concerned with seismic zonation has evolved to include seismoloists and engineers concerned with probabilistic approaches to earthquake damage and a planner to assist in the information transfer from scientists and engineers to city, county, and regional planning staffs. Three events have encouraged communities to attempt seismic zonation: passage of the Alquist Priolo Act by the California Legislature requiring special studies in zones encompassing potentially and recently active faults, preparation and adoption of seismic safety plan elements by cities and counties as required by California statute, and further development of a seismic zonation method. The method has four steps: postulating an earthquake of a given size and location; grouping geological materials with similar physical properties; predicting effects of the postulated earthquakes for each geologic unit by type of hazard of failure, namely surface rupture, ground shaking, flooding, liquefaction potential, and landsliding; and combining geologic effects by zones on the map (fig. 1). Examples of seismic zonation at various scales by cities and counties in the San Francisco Bay region show that scientific information can be used effectively in avoiding earthquake hazards and mitigating damage. Six examples were presented at the Second International Conference on Microzonation in 1978 and reprinted in a Survey Circular on the progress on seismic zonation. The method has been used in California by the cities of Mountain View, Novator, and San Francisco and the counties of Marin, Santa Clara, and San Mateo to develop zones which were used as a basis for their general plans, seismic safety plans, development policies or odrinances. Two of these examples, a city and a county, are described here.

California↗
USGS1985

Reducing losses from earthquakes through personal preparedness

Actions to reduce earthquake hazards can be divided into five phases:two occur before the event, one during the event, and two after the event. The phases are: (1) Mitigation techniques taken anywhere from 1 to 20 years before the event, (2) preparedness measures taken 1 to 20 weeks before the event, (3) response during the actual event, (4) recovery operations over 1 to 20 weeks, and (5) reconstruction activities taken from 1 to 20 years. The magnitude of the earthquake and the resources available to communities and individuals will very these times. A prerequisite to personal preparedness is familiarity with and concern about the other hazard-reduction phases. Strengthening the structure of the home, storing water, and showing family members how to shut off utility-supply lines are only a part of personal preparedness. Equally important are other phases such as picking up children from an evacuated school, securing heavy objects at the work palce as well as in the home, and retrofitting the commuter-highway overpasses needed to reunite a family.

Earthquake Information Bulletin (USGS)↗
USGS1978

Radon emanation on the San Andreas Fault

Radon is a radioactive gas with a half-life of 3.8 days. (Half-life is the time required for the substance to lose half of its radioactivity by decay.) It is itself produced by the decay of uranium. Radon is constantly emanated from the Earth into the atmosphere. Many cases are known where anomalously large amounts of radon have been given off along active faults. THe radon emanation has shown variations with time that are related to changing atmospheric conidtions and possibly to nearby seismic activity.

California↗
USGS1984

Stalking the next Parkfield earthquake in Central California

Looking southeast from Middle Mountain toward Gold Hill, it is a subtle furrow in the grassy knolls of the Cholame Valley of California's Coast Range. To geophysicists, this 19-mile section of the San Andreas fault midway between San Francisco and Los Angeles is the most well understood, most intensely monitored fault in the world. As such, it is also the most likely place for American earthquake researchers to become earthquake predictors. The present understanding of the fault has already prompted speculations that the next moderate Parkfield earthquake will strike in early 1988, give or take a few years. Perhaps more importnat, the next rupture of the Parkfield section of the fault could get out of hand and create a much larger earthquake.

California↗
USGS1982

Volcanic hazard alert issued for the Long Valley-Mono Lake area of California

The ski resort of Mammoth Lakes, nestled against the east front of the Sierra Nevada just east of Yosemite National Park, knows about natural hazards. It is still being shaken by an unusual sequence of earthquakes that started in 1978 and included four earthquakes of magnitude 6 within 48 hours of each other in May 1980. An earthquake hazard watch is still in effect.

California↗
USGS1980

The Southern California uplift revisited

The earthquake that struck Livermore, east of San Francisco, on January 24 was the second moderate earthquake to have occurred in the San Francisco Bay area in 5 months. It raised familiar questions. Does this mean that the "Big One" is coming? Is the theater of heightened concern now in northern California.

California↗
USGS1984

Likelihood of volcanic eruption at Long Valley, California, is reduced

A relatively low level of earthquake activity as well as reduced rates of ground deformation over the past year have led U.S Geological Survey scientists to conclude that the likelihood of imminent volcanic activity at Long Valley, California, is reduced from that of mid-1982 through 1983.

California↗
USGS1983

Seismology in Chile

The Department of Geology and Geophysics, which is under the faculties of Mathematics and Physical Sciences of the University of Chile, is the organization that is responsible for the Seismological Service of Chile and for installing,operating, and maintaining the seismological stations as well as all the strong-motion stations in Chile.

Earthquake Information Bulletin (USGS)↗
USGS1980

The size of earthquakes

How we should measure the size of an earthquake has been historically a very important, as well as a very difficult, seismological problem. For example, figure 1 shows the loss of life caused by earthquakes in recent times and clearly demonstrates that 1976 was the worst year for earthquake casualties in the 20th century. However, the damage caused by an earthquake is due not only to its physical size but also to other factors such as where and when it occurs; thus, figure 1 is not necessarily an accurate measure of the "size" of earthquakes in 1976. the point is that the physical process underlying an earthquake is highly complex; we therefore cannot express every detail of an earthquake by a simple straightforward parameter. Indeed, it would be very convenient if we could find a single number that represents the overall physical size of an earthquake. This was in fact the concept behind the Richter magnitude scale introduced in 1935.

Earthquake Information Bulletin (USGS)↗
USGS1978

Tiltmeter studies in earthquake prediction

Our knowledge is still very limited as to the way in which the Earth's surface deforms around active faults and why it does so. By far the easiest method of providing clues to the mechanisms involved is to record the associated pattern of tilt of the Earth's surface. tilt measurements give us a means of monitoring vertical displacements or local uplift of the crust. The simplest type of tiltmeter is a stationary pendulum (fig. 1). As the Earth's surface distorts locally, the pendulum housing is tilted while, of course, the pendulum continues to hang vertically (that is, in the direction of the gravity vector). The tilt angle is the angle through which the pendulum housing is tilted. The pendulum is the inertial reference (the force of gravity remains unchanged at the site), and tilting of the instrument housing represents the moving reference frame. We note in passing that the tiltmeter could also be used to measure the force of gravity by using the pendulum in the same way as Henry Kater did in his celebrated measurement of g in 1817.

Earthquake Information Bulletin (USGS)↗
USGS1978

Tectonomagnetic effects

Measurements of the actual stress within the Earth and its changes with time are very difficult. It is much easier to monitor the direct effects of this stress, such as ground strain, or the indirect effects, such as changes in resistivity, strain, changes in seismic velocity or changes in magnetic field, and so forth. The latter technique is one of the more promising methods for monitoring substantial volumes of the Earth's crust near active faults with only a few instruments. It derives from the piezomagnetic properties of rocks (that is, the change in rock magnetization and, therefore, local magnetic field due to a change in applied stress). AS stress and strain fields along active faults vary, these variations should be reflected in changing local magnetic fields. In particular, rapidly changing fields might be expected to occur just before a large earthquake. We know that earthquakes result from the sudden release of elastic strain, the end product, most likely, of a long period of gradual stress accumulation in the crust. At the U.S Geological Survey, our magnetic fields studies have two main directions. First, a determination of the magnetic behavior accompanying shallow earthquakes (seismomagnetic effects). Second, a long-term monitoring of the magnetic field in the vicinity of an active fault to detect magnetic changes due to general tectonic activity, particularly that which ultimately leads to earthquakes. These magnetic changes are generally termed "tectonomagnetic effects."

Earthquake Information Bulletin (USGS)↗
USGS1978

Continuous strain measurements near the San Andreas Fault

Changes in the state of stress in the Earth's crust produces corresponding changes in the state of strain and may result, as a consequence, in damaging earthquakes. Monitoring ground strain can, therefore, help us in understanding how stress changes occur and when they are likely to lead to this kind of abrupt release of seismic energy.

California↗
USGS1980

A grassroots movement in Glendora, California

DeLaine Morgan is a teacher at Sandburg Junior High School in Glendora, Calif. Because of her efforts, the Glendora Unified School District is establishing an earthquake preparedness program in each of the District's schools. The following interview relates how this program got started and what individuals can do to get earthquake preparedness programs started in their own communities.

California↗