Seismologists have been predicting for decades thata great earthquake, the “Big One”, will occur in the San Andrés faultand devastate the overcrowded California region. This same prediction was made for Japansince the Great Kanto earthquake in 1923which devastated the Tokyo region and caused 150,000 victims. From recent events, Spanish experts deduce thatthe country of the Rising Sun suffered its “Big One” on March 11.
The energy produced by the friction of tectonic plates has been accumulating for decades in the region of the epicenter of the earthquake of magnitude 9.0 on the Richter scale that shook Japan a few days ago. On March 9, the sudden release of this energy began with a magnitude 7.2 earthquake. On the 11th, the main event occurred, the “Big One”, with a magnitude of 9.0, and was followed in the following days by hundreds of aftershocks of magnitudes greater than 6 and 7 that continue to shake the already battered country, as explained in a press release from the Complutense University of Madrid (UCM).
Japan is within the“Pacific ring of fire”. This ring is a narrow strip that borders the Pacific Ocean characterized by having thehigher rates of volcanic and seismic activity. Four tectonic plates converge in the area: the Eurasian, the Philippine, the North American and the Pacific. The earthquakes are concentrated in the limits of the plates and only 50 kilometers south of Tokyo, the most populated area of the country, is the boundary between the North American and Eurasian plates. It is precisely at this limit that one of the greatest movements of the tectonic plates on Earth takes place.
The Pacific plate slides below the North American plate at an approximate speed of 9 cm per year, in a process that we call “subduction” and in which a great deformation of the crust occurs and large “reverse” seismic faults are generated. These faults are often the cause of the most destructive earthquakes on the planet and are frequently associated with tsunamis. The preliminary results of the location of the epicenter, its depth and its rupture model indicate that both the main event and the strong aftershocks are related to said subduction.
Japan has a long tradition of great earthquakes and tsunamis, and in factthe word tsunami is of Japanese origin and means “wave of port or bay”. Like many other ancient cultures that populated the seismic zones, Japanese folklore created an explanation for earthquakes. Tradition blamed the action of a giant catfish known as Namazu. This fish lived buried in the mud below the surface of the earth and when the gods wanted to punish the people, they released it so that it stirred and stirred, generating the shaking of the ground. In addition to the historical tsunamis that Japan has suffered, the most recent ones also stand out: 1896, with 27,000 victims, and 1933, with 3,000.
Japan and all the countries surrounding the Pacific Ocean are exposed to tsunamis generated in its vicinity, but they are also subject to transoceanic tsunamis. These tsunamis are generated at one end of the ocean, spread and reach the other end. An example of these was the tsunami generated by the 9.5 magnitude earthquake in Valdivia (Chile) that reached the western Pacific coast, causing considerable material damage and 138 victims in Japan, 32 in the Philippines and 16 in Hawaii.
Japan, being aware of the danger to which it is subjected, is one of the countries that has invested the most inresearch on seismic hazard. They have leading research centers in seismology and earthquake geology. One of their insignia is having the best scientific ship, the Chykiu, with which they can pierce the earth’s crust from the bottom of the sea up to 7 km deep and thus be able to study the seismic faults that cause major earthquakes. When the earthquake struck on March 11, the Chykiu was docked in Hachinohe, a port in northeast Japan, and due to the damage suffered by the tsunami it has had to cancel its current mission.
At the Complutense University of Madrid, seismic faults on the ocean floor are being investigated, especially those linked to subduction processes. This is one of the objectives of the group of researchers led by Andrés Carbó Gorosabel, from the Department of Geodynamics of the Faculty of Geological Sciences of the OCM. During the last decade this group of geologists and physicists has focused on investigating the northeastern Caribbean area; region recently affected byearthquake of January 12, 2010 in Haiti. This earthquakereleased 30 times less energy than Japanand it did not generate a tsunami, but left a balance of approximately 230,000 victims, as the earthquake’s earthquake devastated the weak and vulnerable buildings of Haiti. Cases such as Haiti and Japan show us that seismic faults can remain quiet for decades and even hundreds of years and then release accumulated strain energy suddenly.
