Tsunami

Tsunami (a Japanese word meaning harbor wave) are gravity waves generated by large disturbances of the sea floor caused by volcanic eruptions, landslides or earthquakes. Shallow earthquakes along dip slip faults are more likely to be sources of tsunami than those along strike slip faults. In deep water tsunami travel at approximately 0.2 km/sec as compared to 5-10 km/sec for P waves and S waves. Thus, approaching tsunami can be detected by sea floor pressure gauges which measure the height of the water column above the gauge. Tsunami warning systems consist of networks of such gauges connected to a control center. A scale of magnitude for tsunami, similar to the Richter Magnitude scale for earthquakes, is based on logarithm of wave height corrected for distance from the source. The first motion (up-crest or down-trough) can be used to determine direction of sea floor displacement in the source area.