Slips along rock faults cause movements {earthquake}|. Slow plate movements and collisions lead to sudden shifts of one plate against the other. Earthquakes can be several miles deep or even in mantle under ocean trenches. After earthquake, Earth vibrates at low frequency for several days. About 20 major earthquakes and 10^6 minor ones happen each year. Major earthquakes have been in China 1976, Tokyo 1923, San Francisco 1906, Lisbon 1755, Calcutta 1737, and China 1556.
Rock has big cracks {joint, rock}.
Earthquakes can be along rock fractures {fault}|.
Instruments {seismograph}| can measure Earth movements.
Seismographs can use logarithmic scales {Richter scale}|, from 1 up. Largest earthquake was 8.5.
Earthquakes {silent earthquake} can be slow and quiet. Perhaps, water percolation from rain or from trapped water in rocks causes them.
Earthquake shaking can cause loose wet sandy soil to become like quicksand {soil liquefaction}|.
Earthquakes under ocean can make fast waves, which then slow near shore and bunch to make towering waves {tsunami}|.
Earthquake shocks can travel through crust as slow surface waves or through Earth interior as very fast primary waves {P wave}.
Earthquake shocks can travel through solids as fast secondary shock waves {S wave}.
5-Earth Science-Planet-Plate Tectonics
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Date Modified: 2022.0225