RESEARCH ON EARTHQUAKE PREDICTION AND RELATED AREAS AT COLUMBIA UNIVERSITY

Abstract

This paper reviews work at Columbia University on earthquake prediction and related subjects. A series of small earthquakes was triggered by high-pressure fluid injection in western New York near the town of Dale in 1971. The fluid pressures observed at which the earthquakes were turned on and off is similar to that calculated by the Hubbert-Rubey theory. The hydraulic diffusivity was estimated as 1 to 2 times 105 cm2·sec-1. This value is very similar to that obtained for earthquakes related to fluid injection at Denver and Rangely, Colorado and Matsushiro, Japan. In each one of these four cases of earthquakes related to fluid injection fluids appear to have been injected into a major fault zone. Since the hydraulic diffusivities are nearly the same as those estimated from plots of earthquake precursory times and the length of the rupture zones squared, it seems likely that fluids play an important role in the precursory phase of earthquakes. The Lamont group has been making a major study of intraplate earthquakes in New York State and vicinity for the past 7 years. This has included installing a network of about 35 short-period seismograph stations that are telemetered to Lamont. The network recorded the earthquakes from western New York related to fluid injection as well as two swarms of earthquakes at Blue Mountain Lake of which the larger events have been preceded by changes in seismic velocity. Thus far very little has been known about intraplate earthquakes in eastern North America even though a number of damaging shocks of that type have occurred in the last 300 years. An understanding of these shocks has become important since most of the nuclear power reactors in the United States are located in the eastern one third of the country. Two northwesterly trending zones of seismic activity in South Carolina and in New England appear to be situated along the landward continuation of two major fracture zones that were active in the early opening of the Atlantic. Similar zones of seismic activity and of relatively young alkalic rocks are found in similar locations in Brazil, western and southern Africa and southern Australia. Networks of telemetered seismograph stations were installed by the Lamont group about three years ago in the northeast Caribbean, the Alaska Peninsula and eastern Aleutians, northern Pakistan, and around the Nurek Dam in the U.S.S.R In the Aleutians the seismic zone is remarkably thin and is relatively simple. In the region of continent-continent collision in northern Pakistan the downgoing seismic zone is more complicated and appears to consist of at least two zones of activity that extend to depths of about 70km. A major seismic gap for great earthquakes appears to be present along the northern Antillean arc in the Caribbean where underthrusting is of the more typical variety, that is perpendicular to the arc. Another seismic gap appears to exist north of Puerto Rico where the region has not had a great earthquake in at least 400 years. The tectonics of that region is more complicated since slip occurs very nearly parallel to the arc and consists of thrust faulting along nearly horizontal planes. Although the direction of slip is in accord with the overall motion of the Caribbean plate with respect to the Americas plate, the overall mechanics of slip is not well understood. Hence, it is difficult to say with certainty whether the region never has great earthquakes or if the region is a seismic gap in which a great earthquake will eventually occur. Tiltmeters, tide gauges, and other means of monitoring crustal deformation are being employed in two test areas in the Caribbean and on the Alaska Peninsula by the Lamont group.