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Filter Circuit Board for Earthworm Seismic Data Acquisition System

Filter Circuit Board for Earthworm Seismic Data Acquisition System

A seismic network data acquisition and processing system developed by the U. S. Geological Survey, Earthquake Hazards Team (USGS, EHZ) and Dr.Carl Johnson.
When the system was initially developed the multiplexer boards were modified by adding passive filter circuits to each channel in order to eliminate electronic noise picked up in cabling. It was later discovered that a small amount of crosstalk occurred between any given channel and the channel immediately following it in the digitizing sequence. This crosstalk was measured at a ratio of approximately 49dB (280:1). Though small, during digitization of large amplitude signals it will cause what appear to be small earthquake arrivals at the wrong time on some channels. This can result in erroneous calculation of earthquake arrival times, particularly by automated algorithms, unless recognized by human analysts. Furthermore, even when crosstalk doesn?t cause miscalculated arrival times, it still distorts the recorded data.

Article by Edward Gray Jensen. PDF file.

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