Tokyo earthquake

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The first skyscraper in Tokyo before and after the 1923 earthquake

Earthquakes in Tokyo have shaken the Kantō region three times since 1703 with a quake intensity of Shindo 6 or higher . 1703 from the Genroku earthquake , which was the strongest of the three earthquakes with a strength of M 8.2, 1855 from the Ansei-Edo earthquake , whose strength is estimated at M 7.2 and finally in 1923 from the Taishō earthquake , which with a Strength of M 7.9 caused extensive destruction in Tokyo . Still provide earthquake in Tokyo a big risk.

Classification of Tokyo in the global plate tectonics

300 km south-east of Tokyo, three tectonic plates meet and form a triple point . The plate to the east of the triple point is the Pacific plate , which moves westward at a rate of 76 mm per year and, together with the Japan Rift, forms the plate boundary to the southern Philippine plate and the northwestern Eurasian plate . Meanwhile, the Philippine plate moves northwards under the Eurasian plate at 29 mm per year, forming two subduction zones in the east and west of the Izu Peninsula . The Sagami Trench (east of the Izu Peninsula) and the Suruga Trench (west of the Izu Peninsula) are formed along the Eurasian-Philippine plate boundary as a result of subduction . The plate movements along the Suruga and Sagami trenches are blocked so that seismic tensions can build up, which are discharged in earthquakes. Examples are the Taishō (1923) and the Genrokubeben (1703). In contrast, a creeping movement of the Philippine plate is possible north of the Izu Peninsula, so that there is no strong blockage of the plate movements and epicentres in this area are rare.

It has only recently been known that a 90 × 120 km fragment of the Philippine plate is located 35 km below Tokyo between the Eurasian, Pacific and Philippine plates. This fragment likely played a large role in seismic activity at Kantō as it collided with the surrounding plates. This is also the cause of the Ansei Edo quake of 1855. Quakes of the Ansei Edo type therefore differ in their causes from quakes of the Genroku Taisho type. Earlier interpretations assumed that the Philippine plate itself extends at a depth of 90 km to 100 km north of Tokyo and is responsible for quakes in Kantō due to friction with the surrounding plates.

Probability of a strong earthquake in Tokyo

In recent years, the probability of a destructive earthquake occurring has been assessed in two studies: a government study by the Earthquake Research Committee (2005) and a study sponsored by reinsurance company Swiss Re by scientists from the Japanese National Institute of Advanced Industrial and Science Technology, the National Research Institute for Earth Science and Disaster Prevention, the Geographical Survey Institute , the Japan Meteorological Agency, and the United States Geological Survey . The starting point of the study sponsored by Swiss Re are the historical records of 10,000 seismic events over the past 400 years, which have been mapped in a five by five kilometer grid, in which the highest earthquake intensities from 1600 to 2000 are shown. In addition, there are paleoseismic events that can be reconstructed by uplifts along the beaches of the Bōsō Peninsula for the last 7200 years. Since it is assumed that earthquakes occur cyclically in individual faults and the instrumentally documented observation period for earthquakes is just one hundred years, significantly shorter than the return period in most seismically active areas, the historical values ​​create the framework for estimating the probability of future earthquakes Region. A recurrence therefore depends directly on the time that has elapsed since the last earthquake. When looking at several faults in the region, this time dependency is replaced by average values ​​( Poisson probability ). This time-independent method allows predictions of an average number of earthquakes in a certain period of time (e.g. the probability of an earthquake in 30 average years).

In contrast to this, a statement is made for time-dependent probability statements (e.g. the probability of an earthquake in the next 30 years) with the help of the time that has elapsed since a certain earthquake (e.g. Taishō earthquake in 1923), i.e. H. the probability of a quake increases with the passage of time. For both methods, however, a larger number of known earthquakes increases the accuracy of the forecast.

Using both the time-dependent and the time-independent method to determine the probability of a Shindo ≥6 event, the study sponsored by Swiss Re comes to the conclusion that a Shindo ≥6 quake in the next 30 years has a 40% probability for Tokyo , Yokohama and Kawasaki is made up. The government study of the Earthquake Research Committee from 2005, however, assumes a much larger region in its calculations for a strong earthquake in Tokyo, which is why the probability of occurrence is significantly higher: Over a period of 30 years, the study calculates a probability of occurrence of 70%.

When calculating the probability of occurrence, however, both the government study and the study sponsored by Swiss Re come to the conclusion that the higher risk of an Ansei-Edo-type earthquake (1855) than of a Taisho-Genroku-type earthquake (1703 , 1923), since the epicenter of an Ansei-Edo earthquake would be in the immediate vicinity of Tokyo and the time “overdue” of such an earthquake is significantly higher.

For example, the study sponsored by Swiss Re indicates a probability of less than 0.5% that there will be a Taishō-Genroku-type earthquake in the next 30 years. In the government study, too, this probability is less than 0.8%.

Expected damage

In May 2006 the government of the Tokyo prefecture published a study of the damage to be expected in the event of an earthquake with an epicenter below the metropolitan area of ​​Tokyo. The study assumes an M7.3 earthquake with an epicenter in northern Tokyo Bay at 6:00 p.m. in winter. The wind is blowing at 15 m / s. In the study, the damage caused by the quake is estimated as follows: 6314 fatalities and 160,860 injured, including 124,501 seriously injured. A total of 471,586 buildings are damaged, 126,523 of them by earth moving and 345,063 by fires. This results in 41.83 million tons of rubble. A damage assessment by the Earthquake Committee of Tokyo Metropolitan Government in 1971 even assumed 500,000 fatalities at an assumed wind speed of 12 m / s.

Control of earthquake risk

The control of the earthquake risk in particularly endangered districts of Tokyo can on the one hand be taken over by the citizen himself by building his residential property with means of architecture earthquake-proof or retrofitting existing real estate (so-called retrofitting), or on the other hand by urban planning , by considering a threatened cityscape the earthquake security improved. Private initiatives for earthquake-proof construction and retrofitting are promoted in Japan with the law for the promotion of the repair of earthquake resistance (Taishin kaishu sokushin hō) and the law for the restoration of densely populated urban areas (Misshu shigaichi seibi hō). The private initiatives are funded because studies on the effects of earthquakes on wooden houses show that even simple repairs, for example through bracing and anchoring on the basic structure, can effectively contribute to the stability.

Promotion plan for the creation of a disaster-proof city

The most important program for large-scale urban restructuring in Tokyo is the funding plan for the creation of a disaster-protected city (Bōsai toshidsukuri suishin keikaku) of the Tokyo Metropolitan Government. The support plan, which dates from 2003, aims to secure the urban structure against fire and earthquakes through targeted measures. The funding plan was drafted during the revision of a plan designed in 1981 to create disaster-protected circles of life (bōsai seikatsu ken). Bōsai seikatsuken are based on the districts for elementary and middle schools (around 65ha), each of which is to be equipped with infrastructure in such a way that it becomes unnecessary for the residents to leave the area in the event of a disaster.

The idea of ​​the Lebenskreise is to upgrade existing neighborhoods with firebreaks and other infrastructure so that they do not have to be left in the event of a disaster. A total of 820 life circles for 12 million people are planned for the Tokyo region. However, the implementation of the project was very slow, so that the life circles have only been implemented in three Tokyo model districts.

At the moment, projects to create circles of life are only being implemented through the funding plan for the creation of a disaster-protected city. For this purpose, in 2003, within the framework of the funding plan, individual urban areas, which stand out due to their dense development with wooden houses and old buildings, with their respective focus areas of the city, were selected for repair. In the main city districts, in particular, protection against large-scale fires is to be increased through fire protection aisles, evacuation roads and space for the use of rescue vehicles. According to the funding plan, all of the measures should be completed by 2025, with the measures in the priority city districts being completed by 2015.

The funding plan takes into account a total of 27 areas with an urban area of ​​6,500 hectares, of which 2,400 hectares are in eleven key districts. In the priority city districts, the implementation of the measures is to be accelerated by involving the population. To this end, the structures of the Machizukuri approach, urban planning at the micro level, are to be used with a bottom-up approach. However, this large-scale approach is also viewed critically. Most of the above-mentioned measures for urban restructuring are long-term measures that have an impact on the area in question over a large area and usually with the use of large financial resources.

Fire protection measures

As part of urban restructuring, much of Tokyo’s disaster risk management relates to fire prevention and control measures. Direct lessons were drawn from the past, in which Tokyo was largely destroyed by fire in 1923 by the Kanto quake and in 1945 by the area bombing of World War II. Another focus of fire protection measures is urban planning and corresponding land use. This includes three core urban planning elements:

  1. fire-limiting building structures
  2. Evacuation areas
  3. safe control centers and escape routes from which countermeasures can be initiated.

Fire-limiting building structures

For the construction of fire-safe buildings, the Tokyo Metropolitan Government has divided 56,533 hectares of Tokyo into two fire-protection districts: First, a fire-safe district in which all buildings with more than three floors or more than 100 m² are made of non-flammable material (e.g. reinforced concrete) and, secondly, a quasi-fire-proof district in which relaxed regulations only apply to a few larger and taller buildings. The district within the ring of city motorway 6 is marked as a fire-safe district. In addition, the use of fireproof building materials is subsidized in some areas, with these areas accounting for only 1% of the area of ​​Tokyo. Another element of the building structures that contain the fire are streets that function as firebreaks.

Evacuation areas

Evacuation area in Shibuya, Tokyo.

Concerning. of the second core element of urban planning control measures, the design of evacuation areas, open spaces for the event of a disaster in Tokyo are divided into two categories: firstly into evacuation areas (Kōikihinan basho) and secondly into disaster collection points (Hinanjo).

Hinanjo are set up in their basic function as an evacuation area for the residents. However, there are also options for using sanitary facilities and for supplying drinking water.

Kōikihinan basho are evacuation areas that offer enough open space to be able to leave the nearby disaster collection point that has already been visited in the event of an earthquake disaster, if, for example, further consequential accidents occur in the vicinity of the collection point. So far, 189 evacuation areas have been officially defined in Tokyo, which are checked every five years in order to be able to react to changes in the population or changes in urban space.

If one compares Tokyo with cities of similar importance and size in North America and Europe (e.g. New York , London etc.) it is noticeable that there are far fewer open spaces and especially parks, so that in Tokyo there are often schoolyards or other unconventional areas such as z. For example, the Shinkansen train depot in Shinagawa or the runways at Haneda Airport can be used. In addition, four of the eleven former US military bases in Tokyo (meanwhile returned under Japanese control) with a total area of ​​244 hectares were designated as official evacuation areas by the city. Each evacuation area should have at least 1 m² of space per person and, according to government guidelines, no one should have to travel more than two kilometers to the next area.

Corresponding areas only offer sufficient protection from the heat radiation of a large fire if they are surrounded by a barrier at least 30 m high (e.g. apartment blocks). In addition, the distance to the fire must be at least 1.5 times the height of the barrier. However, if the barrier is broken by intersecting streets, the distance should be three times the height of the barrier. Experiments show, however, that the protection against heat radiation in the evacuation areas can be significantly improved by a double barrier (for example consisting of two rows of skyscrapers along a street). However, not all areas in Tokyo meet these requirements. In the case of a wildfire, the case could arise that the fire spreads to the evacuation area and that it can no longer be used to the full extent due to the heat radiation, or has to be abandoned.

In order to be able to fight a fire near the evacuation area in such a case, most evacuation areas (and also most of the disaster collection points) are equipped with water basins that are used in everyday life, for example as a pond or school swimming pool. However, the fact that only 30% of the administrative districts in Japan have designated disaster collection points for old, sick and disabled people is viewed critically. These disaster collection points are supposed to provide basic medical care and also have access to disabled people. Although 60% of the administrative districts of Japan have such facilities, only half of them are publicly marked. The consequences became clear after the Kobe earthquake in 1995 : “In the quake's aftermath, many elderly people in evacuation centers complained that they were experiencing health problems. Despite their advanced age, they were forced to live in the same environment as people without physical problems. " (Basically: after the earthquake, many elderly people in the evacuation centers complained of health problems. Despite their age, they were forced to live in the same environment as healthy people.)

Escape routes

In order to reach the appropriate areas and also to enable emergency services to take action, the question of largely safe roads that can still be used after a strong earthquake must be asked. Refugees and rescue workers are faced with the problem that on the one hand roads can be destroyed and on the other hand the still functional roads are burdened with an unusually high volume of traffic. Exactly these problems also occurred when rescue workers were deployed after the Kobe earthquake (1995).

literature

  • R. Emmermann: System Earth - our dynamic planet. GeoForschungsZentrum Potsdam, Potsdam 2002.
  • W. Flüchter: Geo-risk area Japan: Physiogenic vulnerability and preventive disaster control. In: R. Glaser, K. Kremb (Ed.): Planet Earth: Asia. Scientific Book Society, Darmstadt 2007, pp. 239–251.
  • Jishin chōsa kenkyū suishin honbu [Earthquake Research Committee]: Zenkoku wo gaikan shita jishindo yosokuchizu hōkokusho [Report: 'National Seismic Hazard Maps for Japan]. Jishin chōsai inkai, Tokyo 2005.
  • S. Kakuchi, T. Yoshikawa, I. Nakabayashi: Dōro kyōai chiiki ni okeru sumikiri no secchi to kogata shōbōsharyō no dōnyū ni yoru kanōsei no kaizen kōka ni kansuru kisoteki kōsatsu [The basic study of the effect of improving the possibility to be achieved of corner cut and deployment of small fire engines in district with narrow streets (Sic!)]. Nihon kenchiku gakkai keikakukei ronbunshū. In: Journal of architecture and planning. (619), 2007, pp. 125-132.
  • S. Kuroda: Bunkoban Tōkyō toshizu [Tokyo city map guide]. Shobunsha Publications, Tokyo 2006.
  • I. Matsuda: Natural Desasters and Countermeasures for the Tokyo Lowland. In: Geographical Review of Japan. 63 (Ser. B) (1), 1990, pp. 108-119.
  • Y. Mifune: Chiiki-chiku bōsai machizukuri [Machizukuri district disaster control]. Ohmsha, Tokyo 1995.
  • Münchener Rückversicherungs-Gesellschaft .: Megacities - Megarisks: Trends and challenges for insurance and risk management. Munich Reinsurance Company, Munich 2005.
  • I. Nakabayashi: Bōsai machizukuri no shōrai tenbō - Shimin to kyodō suru bōsai machizukuri no jissen mezasu [Outlook on the future disaster protection Machizukuri - with the aim of a disaster protection Machizukuri practice by citizens and community]. In: Shobō kagaku to jōhō. 79, 2005, pp. 20-25.
  • A. Özerdem, T. Jacoby: Disaster Management and Civil Society: Earthquake Relief in Japan, Turkey and India. Tauris, London 2006.
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  • Tōkyō toshi seibi kyoku shigaichi seibibu kikakuka [Planning Office, Department of Urban Development, Office of Urban Development, Tokyo Metropolitan Government]: Shinsaiji kasai niokeru hinan basho oyobi hinandōri nado no shitei [Determination of evacuation rooms and streets] in the event of fire caused by earthquake. Tokyo Metropolitan Government, Tokyo 2008.
  • Tōkyō-to toshi seibikyoku [Bureau of Urban Development Tokyo Metropolitan Government]: Jishin ni kansuru chiiki kikendo sokutei chōsa (dairoku kai) hōkokusho [report of the sixth earthquake-related report on the measurement of regional hazard]. Tokyo 2008.
  • F. Yamazaki, O. Murao: Vulnerability Functions for Japanese Buildings based on Damage Data from the 1995 Kobe Earthquake. In: AS Elnashai, S. Antoniou: Implications of Recent Earthquakes on Seismic Risk: Papers Presented at the Japan-Uk Seismic Risk Forum 3rd Workshop, 6-7 . April 2000, Imperial College, London, Uk. Imperial College Press, London 2000, pp. 91-102.

Individual evidence

  1. ↑ a b c d R. Stein, S. Toda, E. Grunewald: A new probabilistic seismic hazard assessment for greater Tokyo. In: Philosophical Transactions - Royal Society of London Series a Mathematical Physical and Engineering Sciences. 364, 1845, 2006, pp. 1965-1988. doi: 10.1098 / rsta.2006.1808
  2. ^ M. Ishida: Geometry and relative motion of the Philippine Sea plate and Pacific plate beneath the Kanto-Tokai district, Japan. In: Journal of Geophysical Research. 97 (B1), 1992, pp. 489-513.
  3. ↑ a b c d e f M. Bertogg, M. Guatteri, S Tschudi: Large earthquakes in the Tokyo area. (PDF; 2.0 MB). Swiss Reinsurance Company, Zurich 2005.
  4. ^ G. Schneider: Earthquake - An introduction for geoscientists and civil engineers. Spectrum Academic Publishing House, Munich 2004.
  5. ↑ Shuto chokka jishin ni yoru tōkyō no higai sōtei hōkokusho (Damage estimates of an earthquake with an epicenter in the metropolitan area of ​​Tokyo) ( Memento from May 17, 2009 in the Internet Archive ), 2006. Retrieved on September 22, 2008 from Tōkyō-to bōsai hōmupeiji ( Tokyo Metropolitan Loss Prevention Page)
  6. ↑ a b S. Sato: Urban Renewal for Earthquake-Proof Systems. In: Journal of Disaster Research. 1, 1, 2006, pp. 95-102.
  7. ↑ I. Nakabayashi: Bōsai machizukuri no shōrai tenbō - Shimin to kyodō suru bōsai machizukuri no jissen mezasu (Outlook on the future civil protection machizukuri - with the aim of a civil protection machizukuri practice by citizens and community) . Shobō kagaku to jōhō, 79 2005, pp. 20-25.
  8. ↑ Y. Osawa, M. Murakami, T. Minami, H. Umemura, H. Aoyama, M. Ito et al: 25. Study on the Earthquake Resistivity of Wooden Houses. In: Bulletin of the Earthquake Research Institute. 45, 1967, pp. 473-488.
  9. ↑ Bōsai toshizukuri suishin keikaku (Funding Plan for the Creation of a Disaster-Protected City) ( Memento of August 14, 2007 in the Internet Archive ), 2003. Retrieved on October 20, 2008 from Tōkyō-to Chō, koremade no hōdō happyō (Tokyo Metropolitan Government, previous Press releases)
  10. ↑ a b W. Flüchter: Tokyo before the next earthquake: agglomeration related risks, town planning and disaster prevention. In: Town Planning Review. 74, 2, 2003, pp. 213-238.
  11. ↑ T. Ichiko, N. Takahashi, I Nakabayashi: Revision of disaster prevention measures in Tokyo Metropolitan Government. (PDF; 4.8 MB). Paper presented at the International Workshop on Emergency Response and Rescue 2005. Retrieved December 5, 2008.
  12. ^ Imperial Earthquake Investigation Committee .: Reports of the Imperial Earthquake Investigation Committee. Iwanami Shoten, Tokyo 1925.
  13. ↑ M. Uraya: ( Page no longer available , search in web archives: Anzen, anshin wo mezasu machizukuri "bōsai machizukuri he no keifu" (Urban renewal with the aim of safety: History of civil protection urban development). ) Waseda University, Tokyo, accessed on December 18, 2008.@1@ 2Template: Dead Link / www.waseda.jp
  14. ↑ a b c d Y. Kumagai, Y. Nojima: Urbanization and disaster mitigation in Tokyo. In: JK Mitchell: Crucibles of Hazard: Mega-Cities and disasters in transition. United Nations University Press, Tokyo 1999, pp. 15-55.
  15. ↑ a b c d S. Kuroda: Shinsaiji kitakushien mappu. (Map directory for returning home after an earthquake disaster). Shobunsha, Tokyo 2008.
  16. ↑ Tōkyō toshi seibi kyoku shigaichi seibibu kikakuka (Planning Office, Department for Urban Development, Office for Urban Development, Tokyo Metropolitan Government), (2008): Shinsaiji kasai niokeru hinan basho oyobi hinandōri nado no shitei (Determination of evacuation rooms and earthquakes in fire ). Tokyo Metropolitan Government, Tokyo.
  17. ↑ Earthquakes: Shinagawa City Residents' Open Evacuation Areas ( February 26, 2010 memento on the Internet Archive ), 2008. Retrieved October 19, 2008 from the Shinagawa City website
  18. ↑ Ōta-ku bōsaika (Civil Protection Office of the city of Ōta)
    Ōta-ku bōsai chizu (Civil Protection Card) . City of Ōta, Tokyo 2006.
  19. ↑ a b 30% of local govts have "welfare shelters". In: The Daily Yomiuri. October 31, 2008, p. 3.
  20. ↑ C. Scawthorn, JM Eidinger, AJ Schiff: Fire Following Earthquake. American Society of Civil Engineers, Reston 2005.

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