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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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At least 253 records · Page 14Linked to original sources
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↗
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

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↗
USGS1976

Is there a periodicity in the occurrence of earthquakes?

Various periodicities have been suspected in earthquake activity, but none has yet been proved. In his classic text on seismology, K.E Bullen remarked that small but discernable "trigger" forces, such as tidal effects, temperature changes or barometric changes, have been thought to act as "last straw" phenomena when the earthquake would have occurred anyway.

Earthquake Information Bulletin (USGS)↗
USGS1976

Earthquake prediction; fact and fallacy

Earthquake prediction is a young and growing area in the field of seismology. Only a few years ago, experts in seismology were declaring flatly that it was impossible. Now, some successes have been achieved and more are expected. Within a few years, earthquakes may be predicted as routinely as the weather, and possibly with greater accuracy.

Earthquake Information Bulletin (USGS)↗
USGS1975

Marine terraces; datum planes for study of structural deformation

Along the earthquake-prone coastal area of north-central California, geologists are searching for criteria to establish the nature, extent, and rate of crustal movement or deformation that may be related to activity along known or postulated faults. This search has led to a study of marine terraces along the coast between San Francisco and Santa Cruz in the area that is transected by the Seal Cove-San Gregorio-Palo Colorado fault, a branch of the San Andreas fault system.

Earthquake Information Bulletin (USGS)↗
USGS1980

Children and the San Fernando earthquake

Before dawn, on February 9, 1971, a magnitude 6.4 earthquake occurred in the San Fernando Valley of California. On the following day, theSan Fernando Valley Child Guidance Clinic, through radio and newspapers, offered mental health crises services to children frightened by the earthquake. Response to this invitation was immediate and almost overwhelming. During the first 2 weeks, the Clinic's staff counseled hundreds of children who were experiencing various degrees of anxiety.

Earthquake Information Bulletin (USGS)↗
USGS1977

Remote sensing for lineaments in the Mississippi Embayment

A recurrence of an 1811-12 type earthquake in the Mississippi Valley would pose severe problems to construction in the valley. As William Stauder has stated in the preceding article, a particular difficulty in understanding the seismicity of this area is that, whereas various surface manifestations of the 1811-12 earthquakes have been well documented (for example, sandblows and sunken lands), active fault zones have never been recognized. There may be different reasons for this.

Mississippi embayment↗
USGS1975

The seismic history of the Rio Grande Rift

The Rio Grande Rift, one of the major geologic structures of the Southwest, cuts through the center of New Mexico from north to south. The rift is also referred to as the Rio Grande Trench and as the Rio Grande Trough. It extends from the northern end of the San Luis Valley in Colorado southward 725 kilometres along the course of the Rio Grande River through New Mexico to near El Paso, Tex. The Rio Grande Rift is not a single trough but a series of north-trending basins arranged en echelon and separated by narrow constrictions or channels. The rift follows the western flank of the southern Rocky Mountains and apparently was formed at the same time as the moutains.

Rio Grande↗
USGS1979

Computers at the Albuquerque Seismological Laboratory

The Worldwide Standardized Seismograph Network (WWSSN) is managed by the U.S Geological Survey in Albuquerque, N. Mex. It consists of a global network of seismographs housed in seismic observatories throughout the world. An important recent addition to this network are the Seismic Research Observatories (SRO) which combine a borehole seismometer with a modern digital data recording system.

Earthquake Information Bulletin (USGS)↗