How does a seismometer work?
In simplified form, a seismograph consists of a weight that is separated from the ground by a spring. If the earth moves, as it does during an earthquake, the weight will move differently than the surrounding seismograph mount which is connected to the ground. A seismometer measures precisely the difference between the movement of the weight and the movement of the ground. Then we use this measurement to tell us exactly how the ground has moved. This data is then recorded digitally on a computer disk drive, along with the time from an extremely accurate clock. Why do you use ocean bottom seismometers (OBSs)? We need to obtain measurements with seismographs in all different directions from an earthquake. Measurements only from land seismographs are inadequate to do this, since most of the earth in the Mariana region is covered by water. So the OBSs allow us to observe the earthquakes in all the different directions from the earthquake and thus build up a much more accurate image of eart
