Abstract

A portable array for numerical data acquisition (PANDA) was designed and built in-house at the Center for Earthquake Research and Information (CERI), Memphis State University. The design goal was a transportable set of instruments that could record high-quality seismic data. By making modifications to traditional seismic network technology and using a super-microcomputer workstation for digital data acquisition, this array provides a set of reliable and cost-effective instruments for the collection and analysis of high-resolution seismic data. The field equipment and central recording system are designed to overcome several major limitations in existing seismic network technologies, such as low dynamic range, single-component recording, lack of a common time base between stations, topographic constraints in radio telemetry, and lack of field processing capabilities. PANDA overcomes these limitations. To increase the dynamic range and record full three-component data, each PANDA station has six channels divided into two three-component sets. One set is operated at high gain and the other at low gain, giving a minimum of 90 dB dynamic range. Modular design of the PANDA station electronics facilitates field maintenance and also permits the stations to be run in several additional modes (e.g., with both sets of three channels operating at high gain) or with different sensors on each set. Each telemetry link to the central recording site carries data from two stations (12 channels) by repeating data from an “outer” seismic station through an “inner” seismic station and repeater combination. In addition, several repeat-only stations were built. This ability to repeat signals increases the aperture of PANDA to more than 150 km and overcomes topographic limitations on station locations. Other design features include low power consumption, solar power operation, and transmission of daily calibration and diagnostic signals. These features enable the stations to operate unattended for long periods and provide verification of station performance from the central recording site. The central recording system is based on a high-performance super-micro-computer workstation with a 256 channel A/D front end, which allows both real time digital recording with a common time base and immediate processing of the data. A 40-station network with 6 channels per station uses 240 channels, leaving 16 channels for auxiliary inputs such as time codes and spares. PANDA was field tested in the Arkansas earthquake swarm region from October 1986 to April 1987. It was then deployed in San Juan, Argentina, from August 1987 to May 1988, and in Jujuy, Argentina, from September 1988 to May 1989. A total of more than 20,000 earthquakes were recorded during the two Argentina experiments.

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