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USGS1992

Historical seismicity

The North Coast region of California in the vicinity of Cape Mendocino is one of the state's most seismically active areas, accounting for 25 percent of seismic energy release in California during the last 50 years. the region is located in a geologically dynamic are surrounding the Mendocino triple junction where three of the Earth's tectonic plates join together ( see preceding article by Sam Clarke). In the historic past the North Coast has been affected by earthquakes occurring on the San Andreas fault system to the south, the Mendocino fault to the southwest, and intraplate earthquakes within both the Gorda and North American plates. More than sixty of these earthquakes have caused damage since the mid-1800's. Recent studies indicate that California's North Coast is also at risk with respect to very large earthquakes (magnitude >8) originating along the Cascadia subduction zone. Although the subduction zone has not generated great earthquakes in historic time, paleoseismic evidence suggests that such earthquakes have been generated by the subduction zone in the recent prehistoric past.

California↗

USGS1990

Historical activity at Campi Flegrei caldera, southern Italy

According to the biography of the 6th century Italian lawyer Antonion Castaldo, the swarm of earthquakes that had bothered the inhabitants of Pozzuoli and Naples all summer long ended abruptly on the eve of St. Michael (September 29) in the year 1538. Castaldo recalled that the end of this swarm was heralded by a very large earthquake followed immediately by loud thunder, sounding like bombardment from heavy guns. This was the beginning of a week-long eruption in Campi Flegrei, a volcanic caldera located along the west coast of southern Italy near Naples. This event has been the only eruption of Campi Flegrei in almost 4,000 years. It was preceded by a few decades of sporadic earthquakes swarms and noticeable uplift of the shoreline and was followed by 430 years of quiescence. Signs of renewed activity was first recognized in late 1969. Since then, the caldera center rose as much as 3 meters, and several hundred earthquakes were felt from 1983 to 1984 by people living in Campi Flegrei. These earthquakes extensively damaged buildings in Pozzuoli, located in the center of Campi Flegrei, and prompted the evacuation of 40,000 people. The uplift and the earthquakes stopped in December 1984, and no significant activity has occurred since. We cannot forecast whether the activity since 968 will culminate in another eruption or whether Campi Flegrei will remain quiet for several hundred more years. This article summarizes the historical recorded of activity in Campi Flegrei, which, with varying degrees of reliability, spans 2,000 years, and emphasizes that further scientific studies of this caldera will improve our understanding of the behavior of longquiescent volcanic system.

Earthquakes & Volcanoes (USGS)↗

USGS1988

Measuring contemporary crustal motions; NASA’s Crustal Dynamics Project

In the early and middle 1970's, two new space-based geodetic techniques became available that offered unprecedented accuracy in the measurement of distances over long baselines. As described below, Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) provided a capability to determine in relatively short periods of time the inter-site distance between two observing stations to a level of several centimeters, even if they were separated by thousands or tens of thousands of kilometers. During the 1980's the two techniques have evolved to the point where baselines can now be routinely measured to a level below one centimeter. This is a tenfold improvement in about ten years. Perhaps more important than providing the measurement capability are the consequences of this capability when applied over a few years: the motion of any one site with respect to another can be monitored at the level of better than a cm/yr. This has made possible, for the first time, direct measurement of the motion of the Earth's tectonic plates and of the deformation of its crust in active plate boundary regions. Because such measurements have the potential for providing important information on the mechanisms that drive plates and cause them to slip during earthquakes, a coordinated federal program for the application of this space technology to crustal dynamics and earthquake research was established in 1979. The participating agencies were the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), the United States Geological Survey (USGS), the National Science Foundation (NSF), and the Defense Mapping Agency. NASA formed the Crustal Dynamics Project to further develop the SLR and VLBI techniques, to implement global networks of stations with the cooperation of many different countries, and to conduct measurements of plate motions and regional deformations. this project has grown into an international effort to collect information directly relevant to understanding the threat of the earthquake hazard as well as fundamental research about the crust and upper mantle. In this article we describe briefly the two space geodetic techniques and how they are used by the Crustal Dynamics Project, show some of the very exciting results that have emerged at the halfway point in the project's life, describe the availability and utilization of the data being collected, and consider what the future may hold when measurement accuracies eventually exceed even those now available and when other international groups become more heavily involved.

Earthquakes & Volcanoes (USGS)↗

USGS1992

Elevation changes

The magnitude 7.1 mainshock on April 25, 992, caused substantial changes in the elevation of the Earth's surface in the Cape Mendocino region. Precise measurements of such elevation changes aid in long-term emergency planning and are needed for engineering design and the maintenance of roads, bridges, and waterways. Such measurements also enable researchers to estimate the attitude and slip of the causative fault. Elevation changes, as well as horizontal displacements of the Earth's surface, are an expected consequence of dip-slip displacement on earthquake faults. the rock surrounding and overlying the fault is forced to stretch and bend to accommodate fault slip. Slip in the case of the April 25 mainshock is thought to have occurred on a gently inclined plane dipping to the northeast at a small angle (see article on preliminary seismological results in this issue).The associated fault-plane solution implies that rock overlying the fault plane (the hanging-wall block west and south of the epicenter) rose and shifted to the northeast. The map on the next page shows the location of the epicenter and approximate extent of uplift and subsidence derived from estimates of the geometry, location. and slip on the buried fault plane.

California↗

USGS1983

Research in seismology and earthquake engineering in Venezuela

Venezuela has been affected by destructive earthquakes for the past four centuries. According to entries in the national seismic catalog, there have been about 180 earthquakes which have caused some type of damage to the country. The most catastrophic earthquake occurred on March 26, 1812, on the Bocono fault system and caused widespread destruction in the cities of Merida and Caracas and claimed an estimated 30,000 lives. After the July 29, 1967, damaging earthquake (with a moderate magnitude of 6.3) caused widespread damage to the northern coastal area of Venezuela and to the Caracas Valley, the Venezuelan Government decided to establish a Presidential Earthquake Commission. This commission undertook the task of coordinating the efforts to study the after-effects of the earthquake. The July 1967 earthquake claimed numerous lives and caused extensive damage to the capital of Venezuela. In 1968, the U.S Geological Survey conducted a seismological field study in the northern coastal area and in the Caracas Valley of Venezuela. the objective was to study the area that sustained severe, moderate, and no damage to structures. A reported entitled Ground Amplification Studies in Earthquake Damage Areas: The Caracas Earthquake of 1967 documented, for the first time, short-period seismic wave ground-motion amplifications in the Caracas Valley. Figure 1 shows the area of severe damage in the Los Palos Grantes suburb and the correlation with depth of alluvium and the arabic numbers denote the ground amplification factor at each site in the area. the Venezuelan Government initiated many programs to study in detail the damage sustained and to investigate the ongoing construction practices. These actions motivated professionals in the academic, private, and Government sectors to develops further capabilities and self-sufficiency in the fields of engineering and seismology. Allocation of funds was made to assist in training professionals and technicians and in developing new seismological stations and new programs at the national level in earthquake engineering and seismology. A brief description of the ongoing programs in Venezuela is listed below. these programs are being performed by FUNVISIS and by other national organizations listed at the end of this article.

Earthquake Information Bulletin (USGS)↗

USGS1976

Tragedy at Kilauea

The following article is a reconstruction of events surrounding the deaths of a party of Hawaiian warriors in 1790 on Kilauea Volcano. It suggests that they were killed by a very hot, ash-free, base-surge cloud that rushed from the volcano. Much more recently than that, in the early morning hours of November 29, 1975, the largest earthquake in more than 100 years struck the southern part of the Island of Hawaii, causing widespread faulting and subsidence, an eruption at the summit of Kilauea Volcano, the loss of at least one life, and widespread damage to property. The effects of this earthquake are still being analyzed by the staff of the Geological Survey's Hawaiian Volcano Observatory, but preliminary results indicate that much of the south flank of Kilauea Volcano moved seaward in an abrupt, slump-like manner. The eruption that followed was small by the usually Kilauea standards and is regarded as a leakage of lava from the volcano's underground reservoir system in response to the effects of the earthquake. A more detailed account of these events will be included in a future issue of the Earthquake Information Bulletin.

Hawaii↗

USGS1985

The basin and range viewed from Borah Peak, Idaho.

In 1883, the brilliant geologist G. K. Gilbert wrote an article for the Salt Lake Tribune, "A theory of earthquakes of the Great Basin," which began: There are many geologists who are very wise, but even they do not understand the forces which produce mountains. And yet it must be admitted, not only that mountains have been made, but that some mountains are still rising (Gilbert, 1884). Today, more than a hundred years later, Borah Peak has proved to be among those mountains still rising. During the 28 October 1983 M=7 Borah Peak, Idaho, earthquake, the Lost River Range that Borah Peak caps was lifted 20-30 cm relative to distant points, and was tilted downward away from the range-bounding Lost River fault. The downthrown side of the fault, which subsided as much as 120 cm, was also tilted down toward the fault. The similarity between the earthquake deformation and the cumulative deformation preserved by the dip of strata is striking; it tends to confirm Gilbert's notion that Basin-and-Range topography is built by repeated slip events on normal faults that bound the range. The U.S Geological Survey had just published a preliminary volume of 40 research papers on the Borah Peak earthquake, focusing on the surface faulting, seismology, geodesy, hydrology, and geology of the earthquake and tis setting (Stein and Bucknam 1985). Also included is a field guide to the spectacular earthquake landforms, such as sruface rupture, exploratory trench excavations, sand blows, and landslides.

Idaho↗

USGS2001

Water quality in the eastern Iowa basins

This article summarizes major findings about nutrients in surface and groundwater in the eastern Iowa basins (see map) between 1996 and 1998. The data were collected as part of the U.S. Geological Survey (USGS) National Water-Quality Assessment Program (NAWQA). Water quality is discussed in terms of local and regional issues and compared with conditions found in all 36 National NAWQA study areas assessed to date. Findings are explained in the context of selected national U.S. Environmental Protection Agency (EPA) benchmarks, such as those for drinking water quality and the protection of aquatic organisms. The Eastern Iowa Basins Study Unit includes the Wapsipinicon, Cedar, Iowa, and Skunk River basins and covers approximately 19,500 square miles in eastern Iowa and southern Minnesota. More than 90 percent of the land in the study unit is used for agricultural purposes. Forested areas account for only 4 percent of the land area.

Iowa, Minnesota↗

USGS1987

Failure of a massive earthquake-induced landslide dam in Papua New Guinea

In many areas of the world, landslides dams are both interesting natural phenomena and significant hazards. A few of the these natural blockages attain heights that rival or exceed those of the largest manmade dams. A landslide dam in its natural state differs from a constructed embankment dam in that it is composed of a heterogeneous mass of poorly consolidated earth debris and has no channeled spillway or other protected outlet for its impoundment. Having no outlet, landslide dams upon overtopping very commonly fail by breaching due to erosion by the overflowing stream. Some of the world's largest and most devastating floods have occurred because of the failure of large landslide dams (Schuster and Costa, 1986). This article discusses the recent occurrence of a large earthquake-induced landslide that dammed the Bairaman River in the interior of the island of New Britian, Papua New Guinea, and the subsequent overtopping and failure of this landslide dam.

New Britain↗

USGS1978

Predicting earthquakes along the major plate tectonic boundaries in the Pacific

In an article in the last issue of the Earthquake Information Bulletin ("Earthquakes and Plate Tectonics," by Henry Spall), we saw how 90 percent of the world's earthquakes occur at the margins of the Earth's major crustal plates. however, when we look at the distribution of earthquakes in detail, we see that a number of nearly aseismic regions, or seismic gaps, can be found along the present-day plate boundaries. Why is this? And can we regard these areas as being more likely to be the sites for future larger earthquakes than those segments of the plate boundaries that have ruptured recently.

Earthquake Information Bulletin (USGS)↗

USGS1978

Geodimeter measurements and the Southern California uplift

Modern surveying instruments, such as geodimeters, are capable of measuring distances in the range of 1 to 30 kilometers with remarkable precision. Indeed, the present limitation upon the precision of measurement is not the resolution of the instruments themselves but rather the uncertainty introduced by variations in the velocity of light in the atmosphere between the two endpoints of the measured distance. This capability in precise distance measurement can be applied to earthquake studies by using repeated distance measurements to determine changes in the distance between monuments located along the major faults. Such measurements have been made along the San Andreas fault since late 1959, and, as a result, a wealth of data on crustal deformation in that area is now available. In fact, geodimeter measurements of this type furnish a more stable measure of secular strain (change in the ratio of length to length) than any continuously recording strain meter. The superiority of the geodimeter measurement stems principally from the long base line measured which averages over local inhomogeneities (cracks and joints in the rock, inclusions, and so forth). This article describes the important features of the measurement technique as well as some results for the region of the southern California uplift.

California↗

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)↗

USGS1992

Surface effects of the earthquakes

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.

California↗

USGS1993

Precisely locating the Klamath Falls, Oregon, earthquakes

The Klamath Falls earthquakes on September 20, 1993, were the largest earthquakes centered in Oregon in more than 50 yrs. Only the magnitude 5.75 Milton-Freewater earthquake in 1936, which was centered near the Oregon-Washington border and felt in an area of about 190,000 sq km, compares in size with the recent Klamath Falls earthquakes. Although the 1993 earthquakes surprised many local residents, geologists have long recognized that strong earthquakes may occur along potentially active faults that pass through the Klamath Falls area. These faults are geologically related to similar faults in Oregon, Idaho, and Nevada that occasionally spawn strong earthquakes. In this article we present preliminary results of a close-in, instrumental study of the Klamath Falls earthquake sequence, carried as a cooperative effort by scientists from the U.S Geological Survey (USGS) and universities in Washington, Orgeon, and California. In addition to obtaining much mroe accurate earthquake locations, this study has improved our understanding of the relationship between seismicity and mapped faults in the region.

Oregon↗

USGS1993

Historic and prehistoric earthquakes near Klamath Falls, Oregon

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.

Oregon↗

USGS1993

Volcanic gases create air pollution on the Island of Hawai’i

In a handful of molten magma weighing about a pound, there is less than a tenth of an ounce, by weight, of idssolved gas-roughly the same weight as a pinch of table salt. Yet this tiny amount of gas produces spectacular lava foundations hundreds of meters high (see accompanying photograph). The fountain occurs as magma reaches the surface, because dissolved volcanic gases exolve and expand tremendously as pressure on the magma is released. Anyone who has shaken a bottle of soda and opened it quickly has received the full value of this basic principle of physics. Gases are dissolved in magma at depth, where pressures within Earth's crust are very great-many thousands of pounds per square inch. As the magma rises to the surface and erupts, the pressure decreases, and gas is released. The main gases dissolved in magma are water vapor, carbon dioxide, and sulfur gases, with lesser amounts of others, such as hydrogen, carbon monoxide, hydrochloric acid, and hydrofluoric acid. In our pinch-of-salt-to-a-handful-of-magma illustration above, most of the "pinch" is water vapor, followed by lesser amounts of carbon dioxide and sulfur gases with a few "grains" of hydrogen and other acid gases. The current eruption of Kilauea produces large quantities of volcanic gases that contribute to "volcanic air pollution." In this article we discuss the nature of the gases released from Kilauea, hoe we study them, and what happened to the gases in the environment after they are released.

Hawaii↗

USGS1990

Perspectives on earthquake hazards in the New Madrid seismic zone, Missouri

A sequence of three great earthquakes struck the Central United States during the winter of 1811-1812 in the area of New Madrid, Missouri. they are considered to be the greatest earthquakes in the conterminous U.S because they were felt and caused damage at far greater distances than any other earthquakes in U.S history. The large population currently living within the damage area of these earthquakes means that widespread destruction and loss of life is likely if the sequence were repeated. In contrast to California, where the earthquakes are felt frequently, the damaging earthquakes that have occurred in the Easter U.S-in 155 (Cape Ann, Mass.), 1811-12 (New Madrid, Mo.), 1886 (Charleston S.C) ,and 1897 (Giles County, Va.- are generally regarded as only historical phenomena (fig. 1). The social memory of these earthquakes no longer exists. A fundamental problem in the Eastern U.S, therefore, is that the earthquake hazard is not generally considered today in land-use and civic planning. This article offers perspectives on the earthquake hazard of the New Madrid seismic zone through discussions of the geology of the Mississippi Embayment, the historical earthquakes that have occurred there, the earthquake risk, and the "tools" that geoscientists have to study the region. The so-called earthquake hazard is defined by the characterization of the physical attributes of the geological structures that cause earthquakes, the estimation of the recurrence times of the earthquakes, the estimation of the recurrence times of the earthquakes, their potential size, and the expected ground motions. the term "earthquake risk," on the other hand, refers to aspects of the expected damage to manmade strctures and to lifelines as a result of the earthquake hazard.

New Madrid seismic zone↗

USGS1993

The October 12, 1992, Dahshur, Egypt, Earthquake

Cairo and northeastern Egypt experienced a rare, damaging earthquake on October 12, 1992. The earthquake, which measured 5.9 on the Richter magnitude scale, was centered near the village of Dahshur, about 18 km south of Cairo. The computed hypocentral depth of the earthquake, about 25 km, is consistent with the fact that fault rupture associated with the earthquake did not reach the surface. Despite its relatively moderate size, the earthquake caused many casualties and heavy damage. These losses included more than 500 fatalities, more than 6,500 injuries, and about 8,300 damaged or destroyed buildings. The Foreign Broadcast Service estimated monetary losses directly attributable to the earthquake at $300 million. We were part of an international reconnaissance team that investigated the Dahsur earthquake. This article summarizes our findings and points out how even a relatively moderate sized earthquake can cause widespread damage and a large number of casualities.

Earthquakes & Volcanoes (USGS)↗