According to the China Earthquake Network, a 6.2-magnitude earthquake occurred on the island of Shikoku, Japan (33.05 degrees north latitude, 132.60 degrees Tokyo) at 22:14 Beijing time on April 17 (23:14 local time on April 17). At the same time, according to the Japan Meteorological Agency, the earthquake was felt strongly in the epicenter of Shikoku Island and the surrounding area, but it did not cause a tsunami.
Shikoku Island, Japan
The island of Shikoku is the smallest of the four major islands in mainland Japan, located in the southwestern part of Honshu, south of Chugoku, northeast of Kyushu, and separated from Honshu by the Seto Inland Sea. It is bordered by the Seto Inland Sea to the north, the Pacific Ocean to the south, the Naruto Strait and Kii Suido to the east, and the region of Honshu to the east, and Kyushu to the west by the Toyo Strait and the Bungo Waterway. Together with the island, it covers an area of about 18,800 square kilometers.
Shikoku Island, which is based on Japan's administrative divisions, includes Tokushima Prefecture (Awa), Kagawa Prefecture (Sanuki), Ehime Prefecture (Iyo), and Kochi Prefecture (Tosa), all of which belong to Nankaido, which is historically divided into five provinces and seven provinces. Since it is divided into four countries, it is called Shikoku Island in modern times.
The impact of the earthquake on the island of Shikoku
Shikoku Island is located in the Trough Seismic Zone in the southern waters of Japan, which is part of the Pacific Rim Seismic Zone. This seismic zone is prone to seismic and volcanic activity due to the interaction between the Philippine Sea Plate and the Eurasian Plate, especially the subduction of the Philippine Sea Plate to the Eurasian Plate. Therefore, this earthquake may be just part of the seismic activity in the region, with aftershocks or larger earthquakes likely to occur in the future.
From the point of view of the direct physical impact of the earthquake, due to the high magnitude of the earthquake, Shikoku Island and its surrounding areas will suffer a certain degree of damage to buildings, rupture of roads and bridges, damage to power and communication facilities, etc. Damage to these infrastructures can also lead to disruptions to transportation and communications, affecting the normal life and work of residents. In addition, earthquakes will also cause secondary disasters such as fires, landslides, and mudslides to varying degrees, further aggravating the disaster.
Since the earthquake occurred at night, the earthquake posed a direct threat to the safety of residents. If the buildings in the epicenter area are not able to resist earthquakes, it may cause a certain degree of casualties, and the relevant information on earthquake damage has not been released at present. In addition, earthquakes can lead to safety hazards such as water pollution and gas leaks.
From a social and psychological point of view, earthquakes are bound to bring panic and anxiety to local residents, especially in the context of frequent earthquakes around the world in recent years, and the Japanese people's fear of the destructive power of earthquakes and the possibility of major earthquakes in the future has further increased.
Why didn't the earthquake cause a tsunami?
First, earthquake-induced tsunamis usually require specific conditions. Tsunamis are destructive waves produced by undersea earthquakes, volcanic eruptions, undersea landslides, or meteorological changes. It is mainly controlled by the topography of the seabed, the geometry of the coastline and the characteristics of the waves. Among them, the tsunami caused by an undersea earthquake usually needs to be located within 50 kilometers below the seabed and have a magnitude of 6.5 or more on the Richter scale. This is because larger earthquakes can generate enough energy to push the water into destructive waves.
Although the magnitude 6.2 earthquake on the Japanese island of Shikoku was relatively severe, it did not reach the magnitude of 6.5 or more that is normally required to cause a tsunami, so the energy generated by the earthquake itself may not be enough to cause a tsunami.
Second, the specific location of the earthquake that triggered the tsunami also needs to be considered. If the earthquake occurs in a shallow layer of the seafloor and there is a special seabed topography in the area, such as the edge of the continental shelf, seamounts or submarine canyons, then seismic waves may be more likely to trigger large-scale disturbances in the seawater, resulting in tsunamis.
If the earthquake occurs at a deep seafloor or if the seafloor topography is relatively flat, the disturbance of the seawater by the seismic waves may be relatively small enough to form a tsunami. There is no detailed public information on the location of the earthquake in Japan and its impact on the topography of the seabed, but it is speculated that if the earthquake did not occur in a sensitive area that could trigger a tsunami, the probability of a tsunami would have been relatively low.
After an earthquake occurs, the relevant departments will conduct a comprehensive assessment based on seismic data, seabed topography, meteorological conditions and other factors to determine whether there is a possibility of a tsunami. If the assessment indicates that the tsunami risk is low, then a tsunami warning may not be issued. In the case of the earthquake in Japan, it is possible that the tsunami risk was not high based on this comprehensive assessment, so no tsunami warning was issued.
It is important to note that although the earthquake did not cause a tsunami, it does not mean that similar events will not occur in the future. Therefore, Japan and surrounding areas still need to remain vigilant and strengthen the monitoring and early warning of earthquakes and tsunamis to deal with the risk of possible natural disasters.
#日本四国岛发生6.2 magnitude earthquake#