Earthquake Monitoring
Analog Seismometers
Analog stations are called "analog" because the analog signal is converted into digital information at the site of data processing. This means that the analog signal must be sent, in this case over phone lines, from each station to the central site. Each station's signal is then converted from analog to digital by hardware and processed by computers.
Signals from analog stations go off-scale quickly because the electronics and analog phone lines have limited dynamic range. However, each analog station is somewhat simpler, the time stamping of the data is done simultaneously, and the data conversion hardware is at the central site, so the analog stations are somewhat easier to maintain.
Big Machines
Ranger
The Ranger seismometer was developed in the late 1950/s for a hard (in excess of about 3kg or 6.6lbs) landing on the Moon. The mass weighs about 1.5 kg (about 3.3 lbs) and is actually a suspended ring magnet.
Wood-Anderson
Harry Wood and John Anderson developed the Wood-Anderson seismometer in the 1920's to record local earthquakes in southern California. It photographically records the horizontal motion.
Viking 75
This is a model of the seismometer that was first developed to be placed on the surface of mars in 1976 during the Viking Mars Mission. It records shaking in all three dimensions.
