1964 Niigata earthquake
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| Date | 16 June 1964 |
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| 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 |
| Type | Dip-slip |
| Areas affected | Japan, Niigata Prefecture |
| Tsunami | yes |
| Casualties | 36 dead or missing (385 injured) |
The 1964 Niigata earthquake struck at 13:01 local time (04:01 UTC) on 16 June 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.
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. The earthquake is thought to have occurred due to reverse movement on one of these reactivated faults.
There were 3,534 houses destroyed and a further 11,000 were damaged. 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. 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.
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