Why do we have an earthquake warning bay area?


That is because Japan is situated on the plate boundaries, an area where large strains are earthquake warning bay area accumulated. The surface of the earth is covered with more than a dozen huge plates (plate-like masses of rock). The plates move in different directions at a speed of several centimeters per year (plate motion).

Looking at things on a large scale, most earthquakes occur in the belt-like zones along the plate boundaries. It is said that Japan has been struck by approximately earthquake warning bay area ten percent of the world’s earthquakes. This is despite its small area, being less than one percent of the world’s total land area.

Tremendous forces are applied by plate motion to the inside of the underground rock masses near the plate boundaries. Over many years a vast amount of energy builds up inside the rock masses as a strain and accordingly stress is accumulated. If a rock mass fractures due to the accumulated earthquake warning bay area stress, an earthquake occurs. Japan is situated along the boundaries of four plates.

The large strain energy accumulated in the rock masses therefore cause many earthquakes to be generated. However this doesn’t only apply to the type of earthquakes that occur near the plate boundaries. Earthquakes that occur inland are also thought to be the result of accumulated strain in earthquake warning bay area continental plates.

Along the Japan Trench and the Nankai Trough on the Pacific side of Japan, oceanic plates are continuously moving under the continental plates (subduction). At the same time, the continental plates are being dragged inland.

The subduction of an oceanic plate stresses rock masses around the plate boundary. When the accumulated stress exceeds its limit, a fault movement occurs. This earthquake warning bay area leads the continental plate to rapidly jump up. This movement is a type of earthquake called an inter-plate earthquake.

On the other hand, earthquakes can occur in oceanic plates. The stress accumulated inside the oceanic plate generates a fault movement in the plate; this also causes an earthquake. This type of earthquake is called an intra-oceanic plate earthquake.

In continental plates, indirect forces from plate motion accumulate strain energy. Fault movements occur to release this strain energy in the continental plate. They occur at depths of up to 20 km from the ground surface. When a large-scale fault movement occurs in a continental plate, a fault displacement may develop on or near the ground surface.

The Headquarters for Earthquake Research Promotion calls earthquakes that occur along or around a plate boundary related to a trench or trough a “subduction zone (trench type) earthquake”. It also calls earthquakes that earthquake warning bay area occur at the shallow section of a continental plate a “shallow inland earthquake.”

Earthquakes occur as fault movements. A fault movement is a phenomenon that involves two adjacent rock masses moving in opposite directions to each other along a certain plane (a fault plane). The energy of strain accumulated by plate motion in the rock mass is released in the form of earthquake warning bay area a seismic wave. This is due to abrupt faulting.


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