The initiation and propagation of earthquake ruptures depend upon the mechanical behavior of fault rocks and fluids at depths of several kilometers or more. Using boreholes geophysical measurements in conjunction with laboratory studies, USGS scientists determine the temperature, stress, and fluid-pressure conditions at the depths where earthquakes occur and characterize the mechanical behavior of fault-zone materials at realistic in-situ conditions. This knowledge is combined with surface-based geophysical observations, measurements of tectonic strain accumulation, and other information to yield improved models of the earthquake cycle. Earthquakes occur as a result of global plate motion. However, this simple picture is far from complete. Some plate boundaries glide past each other smoothly, while others are punctuated by catastrophic failures. Some earthquakes stop after only a few hundred meters while others continue rupturing for a thousand kilometers. Earthquakes are sometimes triggered by other large earthquakes thousands of kilometers away.
Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquake is a particular kind of earthquake that are associated with the earth’s crustal deformation; when this earthquake occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium. When large areas of the sea floor elevate or subside, a tsunami can be created. Large vertical movements of the earth’s crust can occur at plate boundaries. Plates interact along these boundaries called faults. Around the margins of the Pacific Ocean, for example, denser oceanic plates slip under continental plates in a process known as subduction. Subduction earthquakes are particularly effective in generating tsunamis.
