Ground Failure Strong ground motion is also the primary cause of damages to the ground and soils upon which, or in which, people must build. One of the most important types of ground failure is known as liquefaction. Liquefaction takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking. Liquefaction occuring beneath buildings and other structures can cause major damage during earthquakes. For example, during the 1989 Loma Prieta, California earthquake, liquefaction of the soils and debris used to fill in a lagoon caused major subsidence, fracturing, and horizontal sliding of the ground surface in the Marina district in San Francisco.
Landslides are another type of ground failure that are often highly destructive.
During the 1964 Anchorage, Alaska earthquake, landslides triggered by very strong local ground motion devastated the Turnagain Heights residential development and many downtown areas in Anchorage. Another important class of earthquake hazards are tsunamis, which are generated by earthquakes which have occurred beneath the ocean floor. Tsunamis are immense sea waves. Japan is one of the most seismically active countries in the world and has experienced many earthquake and tsunamis. These waves travel across the ocean at speeds as great as 597 miles per hour and may be 15 meters 49 feet high or higher by the time they reach the shore.