View from the Lajitas Seismic Observatory across the array

In early 1992 after completing the 21 element GERESS array in Germany, we began to think about how one could reduce the installation and operation expense of telemetered seismic arrays without sacrificing performance. Installing GERESS was a major planning and construction project involving seismometer vaults excavation, miles of cable and conduit trenching, and substantial data communication engineering.

At GERESS, our experience was that one of the major expenses was related to the cable runs and seismic vaults. Not only was the construction itself expensive, but it required substantial time and management in a foreign location. Cutting and trenching operations created an environmental concern. At the time though, there was no alternative.

As GERESS was concluding, there were several informal discussions with other academic seismologists who had experimented with alternative installations. The GPS constellation was almost complete making it possible to get precise world time several times per day. Reasonably priced commercial GPS clocks and receivers were just being developed.

Researchers examining the performance of current NORESS and GERESS style arrays were begining to question to need for 21 elements for all signals in quiet locations. In some cases, array performance was improved by dropping one or more elements. It appeared that choosing a few good sites might be more important than precise geometry control.

This all led to a search to find an inexpensive method to replace the seismometer vault that had to be blasted into hard rock, to avoid the long cable runs that proved expensive and a risk for lightning, and to find a method of installing the eqipment quickly. The search was not unique. Other seismologists had been deploying temporary and permanent networks of seismic stations with elements having some of these characteristics. In our case though, we wished to design an array system from the start that would be capable of unlimited seismic performance, reliability, simplicity, and economy in a fully tested configuration.

Our experience with developing systems led us to conclude that whatever method was developed would have to be tested and refined in the desert at Lajitas, Texas for over a year prior to being considered an operational design.

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