What Makes Earthquake Occurred?
An earthquake is natural phenomenon that the ground is shaking suddenly. The ground shaking of an earthquake is caused by a movement or friction between two tectonic plates. The movement of plate is separated to three types of boundary plates; divergent (the one plate moves far away from the other plate), convergent (the plates move to one another), and transform (the plate move side by side).
These tectonic plates are in the lithosphere layer or crust layer and composed by a stiff material. This layer is separated to two zones, oceanic crust (oceanic plate) and continental crust (continental plate). The crust is driven by asthenosphere which is more fluid than lithosphere. Hence, the plates move with a certain velocity rate. These plates move to each other with relative velocity rate and all these information can be seen in MORVEL and NNR-MORVEL56 plate velocity estimates and information created by DeMets, et.al 2010 and Argus, et al, 2011. A lot of tectonic plates that have been identified (Bird, 2003). The shapefile of plate boundaries is available in repository of fraxen/tectonicplates.
The movement of plate faces a lock condition where one plate is locked by another plate in certain period of time. It will accumulate energy during this process. Once the energy has reached a limit, the energy will be released as an earthquake. The lock condition can be found in the convergent (subduction zone) or transform (shallow fault zone) boundary plate. In the subduction zone, the lithosphere (oceanic plate) subducting beneath another plate (continental plate). The transform plate generate an earthquake on the land and it is called as active shallow crust earthquake or active faults. The depth of earthquake from this source is shallower than from the subduction zone. The global active faults dataset can be found in the repository of Global Earthquake Model, GEM
The earthquake energy generates a vibration to any direction from subsurface to surface. This vibration is recorded by using three components seismometer. The visualization of vibration is then called as earthquake waveform. By using the waveform data, the earthquake location, magnitude, depth, and mechanism can be derived.
Note The image illustrations are public domain from USGS