The widespread use of personal microcomputers by private citizens and the public recognition of seismic hazard following the Loma Prieta Earthquake suggest a new method of monitoring seismological phenomena in the San Francisco Bay Area. It is technically feasible (estimated cost $500-1000) to build a self-contained digital seismic data acquisition unit (SDAU) that would utilize the modem and other resources of a home computer to communicate seismic information to a central processing/archival system (CPAS) minicomputer located at the U. S. Geological Survey in Menlo Park, California. There are approximately 100,000 home microcomputers within a 100 km radius of Menlo Park. If 1% of these users were to participate in the program described here, and if half of those regularly generated reliable data, the resulting array would have an average inter-station spacing of ~10 km. Station density, proportional to population density, would be significantly higher than this value in more developed areas where information about site response is correspondingly more important. The SDAU would digitize seismic signals from a 3-component FBA sensor buried immediately outside the residence and scan these timeseries in realtime for seismic events which, when detected, would be stored in RAM. The rugged construction and built-in battery backup of the SDAU would allow it to operate as a strong-motion accelerometer in the event of catastrophic ground motion. In normal operation, a post-processor would analyze the event timeseries for P- and S-wave phase times, peak amplitudes, durations, etc., and these event parameters would be routinely transmitted by the host microcomputer to the CPAS via telephone. The CPAS, similar to a telephone switching/accounting computer system, would be equipped with ~100 input lines and would maintain an archive of all user calls, i.e., a history of each station. A clock correction to the internal clock of each SDAU would be recorded by the CPAS whenever the host microcomputer uploaded event parameters. Crucial to the success of the proposed data acquisition scheme would be an effective USGS/SDAU-users group which provided software/hardware support and published a monthly newsletter that summarized the results of the array's operation and gave recognition to users distinguished by the completeness and reliability of their data. The integrity of the dataset would be maintained by its redundancy and by its current and comprehensive station history. The high spatial density of stations would permit the use of simple methods of analysis, e.g., tomography and spectral amplitude ratios, and provide a set of seismic observations which approached the scale of geologic observations. In an age characterized by a growing awareness of the fragile and necessary connection between humanity and the Earth and simultaneously by a decline in funding for seismological research, the proposed scheme could provide an unprecedented dual vision of seismic source processes and micro-regional site response which are both critical to the community of the San Francisco Bay Area.

EOS (Transactions, American Geophysical Union) Vol. 71, No. 43, p. 1469, 23 Oct 1990.