What other sensors besides accelerometers are used to measure earthquake motion?
The most common sensor is not the accelerometer, which measures acceleration, but the seismometer, which measures the velocity or speed of a point on the ground as it moves during earthquake shaking. Most velocity sensors are high precision, sensitive instruments designed to record motions from distant earthquakes rather than the strong shaking that occurs near to earthquakes. Another instrument is the displacement sensor, which can be used in certain applications; in strong motion, they are most useful in measuring relative displacement (the distance between two points). Finally, GPS position sensing has become available and can be used to track the position of a point. Earthquake forces changes so rapidly during an earthquake that they must be measured many times each second (as many as 200). GPS doesn’t measure changes that rapid, but is ideal to get final locations after an earthquake.
