Last spring, Hsi-Ping Liu, Russell Sell, and I (JBF) were visiting a seismograph site in the Hayward fault zone deploying one of an array of seismometers to study fault-zone guided waves. We were testing a set of 5-s seismometers that Hsi-Ping had modified to incorporate a novel leveling device. The device would automatically recenter the seismometers each day so that they would be stable for months to years. Hsi-Ping would put a small piece of paper on one of the masses, watch the mass drift for a few seconds, and then trigger the circuit to relevel the mass. It worked...

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