The HYPO71 Earthquake Location Program
W. H. K. Lee, J. C. Lahr, and C. M. Valdes
HYPO71 is a computer program for determining hypocenter, magnitude, and first motion pattern of local earthquakes, and was first released in 1971. It is perhaps the first earthquake location program that achieved worldwide usage, as evidenced by the fact that about 1,000 copies of the HYPO71 manual were requested and distributed (Lee, 1990). It is included here for historical documentation.
Although Geiger (1912) introduced an earthquake location procedure based on the least squares in 1910, it was not a practical procedure until digital computers become common in the 1960s. In the early 1960s, many seismologists around the world wrote earthquake location programs based on the Geiger's method, such as HYPOLAYR (Eaton, 1969) which included a listing of the source code. For ease of routine data processing of a large regional seismic network, the HYPO71 program was written with an emphasis on a simple user interface for batch processing. The original HYPO71 program was dated December 21, 1971, and a user's manual was released (Lee and Lahr, 1972).
In order to generalize HYP071 for worldwide usage and to correct a few programming "bugs", the program HYP071 was revised on November 25, 1973, and a note on "Revisions of HYP071" was released on January 30, 1974. In 1975, all reprints of the original HYP071 manual were exhausted, so the authors took this opportunity to release a revised manual, called HYP071 (Revised) (Lee and Lahr, 1975). When the personal computers were introduced in the early 1980s, a version of the HYP071 program called HYPO71PC, was released by Lee and Valdes (1985). This version was also published in the IASPEI Software Library (see Chapter 85.2 by Lee). Since the HYPO71 program was written in standard Fortran, it could be compiled on most of the computers with hardly any changes.
The distribution files for HYPO71 are on this web site.
Eaton, J. P. (1969). HYPOLAYR, a computer program for determining hypocenters of local earthquakes in an earth consisting of uniform flat layers over a half space, Open File Report, U.S. Geological Survey, 155 pp.
Geiger, L. (1912). Probability method for the determination of earthquake epicenters from the arrival time only (translated from Geiger's 1910 German article), Bulletin of St. Louis University, 8(1), 56-71.
Lee, W. H. K. (1990). Replace the HYPO71 format?, Bull. Seism. Soc. Am. 80, 1046-1047.
Lee, W. H. K. and J. C. Lahr (1972). HYP071: A computer program for determining hypocenter, magnitude, and first motion pattern of local earthquakes, Open File Report, U. S. Geological Survey, 100 pp.
Lee, W. H. K. and J. C. Lahr (1975). HYP071 (Revised): A computer program for determining hypocenter, magnitude, and first motion pattern of local earthquakes, U. S. Geological Survey Open File Report 75-311, 113 pp.
Lee, W. H. K. and C. M. Valdes (1985). HYP071PC: A personal computer version of the HYPO71 earthquake location program, U. S. Geological Survey Open File Report 85-749, 43 pp.
Lee, W. H. K., R. E. Bennett, and K. L. Meagher (1972). A method of estimating magnitude of local earthquakes from signal duration, Open File Report, U. S. Geological Survey, 28 pp.
W. H. K. Lee