Earthquakes in Albuquerque country
— Stuart A. Northrop

New Mexico experienced more than a thousand earthquakes during the period 1849-1975 (Northrop, 1976). Of these, about one-half can be regarded as definitely recorded and the remainder as less definitely or vaguely recorded. The first earthquakes reported in New Mexico occurred at Socorro in 1849. Instrumental studies did not begin until 1959-60 (Sanford and Holmes, 1961a, b) and fairly complete instrumental records are available only after 1962. Thus, we have noninstrumental data from 1849 to the present (a century and a third) compared to instrumental data from 1962 to the present.

Seismograph stations were installed at Denver, Colorado and at Tucson, Arizona about 1909. The first permanent seismograph station in New Mexico was installed in 1960 near the campus of New Mexico Institute of Mining and Technology (Sanford and Holmes, 1961b). In 1961-62, the U.S. Coast and Geodetic Survey established its seismo-logical laboratory (now the U.S. Geological Survey, Albuquerque Seis-mological Laboratory) southeast of Albuquerque and began operating this and other stations at Las Cruces, New Mexico, and at Tucson and Payson, Arizona. The Los Alamos Scientific Laboratory installed a network of stations in the vicinity of Albuquerque in 1976 (Sanford and others, 1981, p. 9).

Most of New Mexico's earthquakes recorded prior to 1962 were located in the Rio Grande rift zone along the Rio Grande Valley, with a notable concentration from Albuquerque to Socorro. Many of these occurred in swarms: Socorro (1849-50), Sabinal and Jarales (1893), Socorro (1904 and 1906), and Belen (1935). Since 1962, many earth-quakes have been instrumentally located throughout New Mexico beyond the rift zone.

This paper reviews the earthquake history of the Albuquerque-Belen area. The area covers one degree of latitude from 34.5° to 35.5° N and one degree of longitude from 106° to 107° W. The map (fig. 1) measures about 91 km east-west and 111 km north-south. Total area is about 10,100 km'. I am indebted to Professor Allan R. Sanford of the New Mexico Institute of Mining and Technology for a critical reading of the manuscript.