Tōkai earthquakes
The Tōkai earthquakes are major earthquakes that have occurred regularly with a return period of 100 to 150 years in the Tōkai region of Japan. The Tōkai segment has been struck by earthquakes in 1498, 1605, 1707, 1854, and 1923.[1] Given the historic regularity of these earthquakes, Kiyoo Mogi in 1969 pointed out that another great shallow earthquake was possible in the "near future" (i.e., in the next few decades).[2]
Given the magnitude of the last two earthquakes, the next is expected to have at least a magnitude scale of 8.0 Mw, with large areas shaken at the highest level in the Japanese intensity scale, 7.[3] Emergency planners are anticipating and preparing for potential scenarios after such an earthquake, including the possibility of thousands of deaths and hundreds of thousands of injuries, millions of damaged buildings, and cities that include Nagoya and Shizuoka devastated. Concern has been expressed over the presence of the Hamaoka Nuclear Power Plant, close to the expected epicentre of a Tōkai earthquake.[2] The Fukushima I Nuclear Power Plant was severely damaged after a large earthquake followed by a tsunami in 2011, causing a nuclear event of level 7, the highest on the scale.
Shortly after the 2011 Tōhoku earthquake, new reports were released which indicated the significant likelihood of another magnitude 9 earthquake occurring elsewhere in Japan, this time on the Nankai Trough. The reports stated that if a 9.0 earthquake occurred on the Nankai Trough, the effects would be very serious. The quake itself would likely kill thousands, and a series of 34-meter (112-foot) tall tsunamis would impact areas from the Kantō region to Kyūshū, adding thousands to the death toll, and destroying Shizuoka, Shikoku, and other areas with large populations.[4][5]
Earthquake prediction
The Japanese government is taking the Tōkai earthquakes seriously and has charged the Japan Meteorological Agency with predicting the next one. There is now a dense array of instruments placed to accumulate a continuous stream of data related to seismicity, strain, crustal expansion, tilt, tidal variations, ground water fluctuations and other variables. They are watching for an anomaly in this data which might precede the next major Tōkai earthquake.
Following the prediction of an earthquake in the relatively near future, and in order to try to predict when it would occur, the Coordinating Committee for Earthquake Prediction (CCEP) designated the Tōkai region as an Area of Specific Observation in 1970, and upgraded it to an Area of Intensified Observation in 1974.[2] Following the passing of the Large-Scale Earthquake Countermeasure Act in 1978, the Earthquake Assessment Committee (EAC) was set up to warn the Prime Minister, via the Japan Meteorological Agency, if the next quake is imminent.[2]
Relation to other major earthquakes
The pattern of historical seismicity reveals that the megathrust surface is segmented, with five separate zones of rupturing identified, conventionally labeled A–E, from west to east.[6] Earthquakes involving the A+B segments are generally referred to as Nankai (literally South Sea) earthquakes, C+D Tōnankai (literally Southeast Sea) earthquakes and E Tōkai (literally East Sea) earthquakes. These earthquakes repeat at intervals generally in the range of 90 – 200 years.
On all but one occasion, rupture of segment C (±D ±E) has been followed by rupture of segments A+B within a few years. This behavior has been reproduced by modeling the viscoelastic response of the megathrust fault plane with lateral variations in both convergence rate and frictional properties.[6]
Historical Tōkai earthquakes
| Date | Magnitude | Name | Death toll | Description | Years since previous earthquake |
|---|---|---|---|---|---|
| November 26, 684 | 8.3 | Hakuhō earthquake | unknown | Landslides. Many houses, shrines and temples collapsed. | NA |
| August 22, 887 | 8.5 | Ninna earthquake | unknown | Many people were killed by collapsing houses. | 203 |
| December 11, 1096 | 8.4 | Kōwa earthquake | unknown | The main building of the imperial palace was damaged, and the big bell of the Tōdai-ji temple fell down. The tsunami in Suruga split houses, and 400 shrines and temples were damaged. | 209 |
| July 26, 1361 | 8.5 | Shohei earthquake | unknown | Considerable damage. | 265 |
| September 11, 1498 | 8.4 | Meiō earthquake | 40,000 | Kai was severely shaken. The buildings around the great Buddha of Kamakura (altitude 7m) were swept away by a tsunami. In Ōminato, Ise 1,000 households were destroyed with 5,000 people drowned. 10,000 people drowned in Ise-Shima, while in Shida District, Shizuoka Prefecture, 26,000 people died. Nankai earthquakes also occurred around the same time, according to the Geological Survey of Japan. | 137 |
| February 3, 1605 | 7.9 | 1605 Keichō Nankaidō earthquake | 2,300 | The tsunami struck from the Pacific coast of Kyushu, Miyazaki, led to the deaths of 57 on the island Hachijō-jima, destroyed 700 houses in a village west of the Kii Peninsula, 1,500 people died in Shishikui Awa, 350 deaths in Tosa Nishinoura, and 400 in the vicinity of Cape Muroto. | 107 |
| October 28, 1707 | 8.4 | Hoei earthquake | 20,000 | Tōkai, Tōnankai and Nankai earthquakes occurred at the same time with magnitude 8.4–8.6. Mount Fuji erupted 49 days after this earthquake and the Hōei crater was created. About 20,000 people were killed and 60,000 houses collapsed, the Tosa area was affected by the tsunami. | 102 |
| December 23, 1854 | 8.4 | Ansei-Tōkai earthquake | 3,000 | The epicenter ranged from Suruga Bay to the deep ocean, and struck primarily in the Tōkai region, but destroyed houses as far away as Edo. The accompanying tsunami caused damage along the entire coast from the Bōsō Peninsula in modern-day Chiba prefecture to Tosa province (modern-day Kōchi Prefecture).[7] | 147 |
See also
References
- Andrew Alden. "The Tokai Earthquake of 20xx". About.com. Retrieved May 19, 2012.
- Kiyoo Mogi (2004). "Two grave issues concerning the expected Tokai Earthquake" (PDF). Earth Planets Space. 56 (8): li–lxvi. Retrieved March 11, 2011.
- The shaking caused by an earthquake is not the same as, and not totally determined by, the energy released. See Seismic scale, Mercalli intensity scale
- Kim Kyung-Hoon (April 1, 2012). "34-meter tsunami may hit Japan after megaquake – report". RT. Retrieved May 19, 2012.
- Elaine Kurtenbach (April 1, 2012). "Japan Tsunami Could Happen Again If Powerful Earthquake Hits: Experts". The Huffington Post. Retrieved May 19, 2012.
- Hirahara, K.; Kato N.; Miyatake T.; Hori T.; Hyodo M.; Inn J.; Mitsui N.; Sasaki T.; Miyamura T.; Nakama Y.; Kanai T. (2004). "Simulation of Earthquake Generation Process in a Complex System of Faults" (PDF). Annual Report of the Earth Simulator Center April 2004 - March 2005. pp. 121–126. Retrieved 2009-11-14.
- Kawade Shobō Shinsha Editorial Team (eds.). "Ansei Daijishin" (安政大地震, "Great Earthquakes of Ansei"). Ō-Edo Rekishi Hyakka (大江戸歴史百科, "Historical Encyclopedia of Great Edo"). Tokyo: Kawade Shobō Shinsha Publishers, 2007. p253.