| 1 | We observe earthquakes with a network of seismometers on the earth's surface. | |
| 2 | It is the radiated energy that shakes buildings and is recorded by seismographs. | |
| 3 | In response, the local meteorological bureau has strengthened its earthquake-monitoring efforts by installing underwater seismometers. | |
| 4 | Early-warning systems consist of seismographs that detect the P-waves and send out electronic alerts. | |
| 5 | Explosions are registered by seismographs and they define the structure of Earth crust. |