1964 Niigata earthquake
  | |
| Date | June 16, 1964 |
|---|---|
| Magnitude | 7.6 Mw |
| Depth | 34 km |
| Epicenter | 38°22′N 139°13′E / 38.37°N 139.22°ECoordinates: 38°22′N 139°13′E / 38.37°N 139.22°E |
| Countries or regions | Japan, Niigata Prefecture |
| Tsunami | yes |
| Casualties | 36 dead or missing (385 injured)[1] |
The 1964 Niigata earthquake struck at 13:01 local time (04:01 UTC) on June 16. with a magnitude of 7.5 or 7.6. The epicenter was on the continental shelf off the northwest coast of Honshu, Japan in Niigata Prefecture, about 50 kilometres (31 mi) north of the city of Niigata. The earthquake caused liquefaction over large parts of the city.
Geology
The northwestern side of Honshu lies on the southeastern margin of the Sea of Japan, an area of oceanic crust created by back-arc spreading from the late Oligocene to middle Miocene. The extensional tectonics associated with the spreading formed a series of N-S trending extensional faults and associated basins. Currently the area is being deformed by contractional tectonics, causing inversion of these earlier basins, forming anticlinal structures.[2] The earthquake is thought to have occurred due to reverse movement on one of these reactivated faults.[3]
Damage
There were 3,534 houses destroyed and a further 11,000 were damaged.[1] This level of damage is explained by the influence of poor sub-soil conditions. Most of the lower part of the city of Niigata is built on recent deltaic deposits from the Shinano and Agano rivers, mainly consisting of unconsolidated sand. Shaking during the earthquake caused liquefaction with instantaneous compaction and formation of many sand volcanoes.[1][3] Maps of areas of subsidence and sand volcanoes were found to match closely with old maps of the position of former river channels. Subsidence of up to 140 cm was measured over wide areas associated with the liquefaction. In one area of apartment buildings built on reclaimed land by the Shinona River, most of the blocks became inclined, one of them being completely overturned. This was despite relatively low levels of ground acceleration recorded by strong motion accelerographs placed in one of these buildings.[3]
Showa bridge
The collapse of the Showa bridge in Niigata has been analysed in detail.[4][5] From eyewitness reports it appears that failure began 70 seconds after the start of the earthquake, suggesting that ground motion was not responsible. Movement of piles beneath the bridge piers due to lateral spreading caused by liquefaction, is regarded as the main cause of the failure.[4][5]
Characteristics
Earthquake
The earthquake had a magnitude of 7.6 on the moment magnitude scale, but the relatively deep focal depth of 34 km meant that the perceived intensities on the coast of Honshu were generally VIII (Destructive) or less on the Mercalli intensity scale, on consolidated ground.[3] The calculated focal mechanism indicates reverse faulting on a west-dipping fault trending N20°E.[6]
Tsunami
The earthquake caused a moderate tsunami with a maximum recorded run-up of nearly 6 m along the coast of Honshu between Shioya and Nezugaseki.[7]
References
- ↑ 1.0 1.1 1.2 USGS. "Historic Earthquakes - Niigata, Japan 1964 June 16 04:01 UTC Magnitude 7.5". Retrieved 10 June 2010.
- ↑ Sato, H.; Yoshida T., Takaya I., Sato T., Ikeda Y. & Umino N. (2004). "Late Cenozoic tectonic development of the back arc region of central northern Honshu, Japan, revealed by recent deep seismic profiling". Journal of the Japanese Association for Petroleum Technology 69 (2): 145–154. ISSN 0370-9868. Retrieved 10 June 2010.
- ↑ 3.0 3.1 3.2 3.3 Kawasumi, H. (1968). "1. Introduction". In Kawasumi H. General Report on the Niigata Earthquake of 1964. Tokyo, Japan: Tokyo Electrical Engineering College Press. Archived from the original on 4 June 2010. Retrieved 10 June 2010.
- ↑ 4.0 4.1 Yoshida, N.; Tazoh T., Wakamatsu K., Yasuda S., Towhata I., Nakazawa H. & Kiku H. (2007). "Causes of Showa Bridge collapse in the 1964 Niigata earthquake based on eyewitness testimony". Soils and Foundations 47 (6): 1075–1087. Retrieved 10 June 2010.
- ↑ 5.0 5.1 Kazama, M.; Sento, S.; Uzuoka, R.; Ishimaru M. (2008). "Progressive damage simulation of foundation pile of the Showa Bridge caused by lateral spreading during the 1964 Niigata earthquake". In Liu H., Deng A. & Chu J. Geotechnical Engineering for Disaster Mitigation and Rehabilitation. Beijing & Berlin: Science Press and Springer-Verlag. pp. 170–176. Retrieved 10 June 2010.
- ↑ Ruff, L.; Kanamori H. (1983). "The rupture process and asperity distribution of three great earthquakes from long-period diffracted P-waves". Physics of the Earth and Planetary Interiors 31: 202–230. Bibcode:1983PEPI...31..202R. doi:10.1016/0031-9201(83)90099-7. Retrieved 10 June 2010.
- ↑ NGDC/NOAA. "NOAA page on the tsunami". Retrieved 10 June 2010.