Earthquakes commonly occur where Earth has a fault or crack in its crust. One big fault runs through most of the state of California. During an earthquake, vibrations travel through the crust. This motion can be recorded by devices named seismographs. Surveyors measure elevation or how high a location is above sea level. They use plaques called bench marks to detect crust movement. Scientists who study Earth are geologists. They try to predict an earthquake by recording tiny movements