In case anyone is interested, there is what looks like a pretty good circuit using in the current issue of Nuts and Volts. The 4 MH RF generator and detector/amplifier circuit look like something that could be easily adapted to a conventional seismometer. The instrument they describe uses liquid mercury and has a period of about 24 seconds. They describe it as sensitive enough to register earth tides. =20In case anyone is interested, there is what looks = like a pretty good circuit using in the current issue of Nuts and Volts. = The 4 MH RF generator and detector/amplifier circuit look like something that = could be easily adapted to a conventional seismometer. The instrument = they describe uses liquid mercury and has a period of about 24 seconds. = They describe it as sensitive enough to register earth = tides.