Seismic intensities, “size” of earthquakes and related parameters

Abstract

The simple model of an earthquake used in Evernden, et al. (1973) was extended to the conterminous United States and observed patterns of isoseismals for major earthquakes studied in relation to the model. Regional attenuation, a known major factor controlling isoseismal patterns, was quantitatively evaluated. Incorporating this regional variation into the model results in the prediction that in terms of energy released, the San Francisco earthquake of 1906 was 50 times as large as Owens Valley 1872 and more than 100 times larger than the Charleston 1886 and New Madrid 1811 earthquakes. All of these were probably of comparable “magnitude”. Other relevant parameters are investigated. Analysis of probability of occurrence of major earthquakes in the Eastern United States suggests average annual return times of intensity X and IX of thousands of years at least. Presently unknown local conditions may lead to much greater probabilities at some localities, and the importance of developing procedures for determining regions of abnormally high risk is stressed.

Journal of Research of the U. S. Geological Survey, 1978, volume 6, issue 1

“…Another implication of a casual relation between mafic intrusives, such as dikes or sills, and earthquakes is that the source dimensions of the earthquakes are likely to be small, that is, less than about 10 km long. This is in agreement with Evernden's (1975) estimates of source dimensions of earthquakes of the eastern United States which are based upon a study of earthquake intensities. Because of low attenuation, however, high intensities may occur over large areas, and, consequently, earthquakes in the eastern United States must be considered hazardous even though they may be of smaller magnitude than those in the western United States.…”

“…Furthermore, attenuation of seismic waves generated by earthquakes in the central and southeastern United States is very low compared to the attenuation of seismic waves generated in the western United States. Low attenuation accounts for the great distances at which earthquakes are felt in the central and eastern United States (Nuttli, 1973;Evernden, 1975).…”

Assessment of regional earthquake hazards and risk along the Wasatch front, Utah

“…The magnitude of the Owens Valley event is more controversial, owing to the lack of seismographic instruments at the time. Magnitude estimates for this earthquake based on felt reports range from 8.3 (Oakeshott and others, 1972) to 7.2 (Evemden, 1975). From the surface faulting, Beanland and Clark (1987) estimate a moment magnitude of 7.5 to 7.7.…”

“…Several studies have examined Modified Mercalli intensity attenuation in broad regions of the U.S. As they pertain to evaluating attenuation along the Wasatch Front in northern Utah, all of these studies have the limitation that the regions considered are much larger than the specific region of the Wasatch Front. The studies by Everndon (1975), Howell and Schultz (1975), Chandra (1979),and Brazee (1980 all indicate a somewhat lower rate of intensity attenuation in the western mountain states than in California.…”

Some aspects of the seismic hazard associated with radioactive waste disposal

“…States. Evernden (1975) believes that the length of faulting in the east is relatively short compared with earthquakes in California and Nevada. If this hypothesis is true, fault length would not be a significant factor in estimating ground motion for earthquakes in the east.…”