Scientists have determined that as water level in a reservoir increases, water pore pressure inside the rocks along local faults also increases. The increased pressure may cause the rocks to slip, generating earthquakes. Earthquakes were rare in the area prior to construction of the dam, but seismographs registered at least 600 shallow-focus earthquakes between 1936 and 1946. Most reservoirs, however, do not cause earthquakes. They have found that the majority of earthquakes occur along plate tectonic boundaries, while there are relatively few intraplate earthquakes earthquakes that occur within a tectonic plate.
Intraplate earthquakes occur within the plates at places where the crust is fracturing internally.
Both interplate and intraplate earthquakes may be caused by tectonic or volcanic forces. Next Page Return to Cosmiverse Reference Library Microsoft Corporation. All Rights Reserved. Cosmic Voyage 2000. All Rights Reserved.