December 20, 1946 Earthquake: S Coast, Honshu, Japan

Reference #414:

On December 21, 1946, at 4:19 [local time] there was a catastrophic earthquake on the southwest of Japan in the Nankai area. It was felt almost everywhere in the central and western parts of the country. The number of homes destroyed directly by the earthquake was 2,598; 1,443 people died. In addition, 1,451 homes were washed away by the ensuing tsunami waves.

The earthquake caused great changes in relief. According to repeated geodetic surveys and other data, the southern prominences of Shikoku Island and the Kii Peninsula (Capes Ashizuri, Fluroto, Shionomisaki), rose 1/2 to 1 m, while the bulk of Shikoku Island and the Kii Peninsula, including the bays on the Pacific coast dropped several tens of centimeters. In addition, Shikoku Island and the Kii Peninsula shifted seaward 1/2 to 2 m. Slow vertical movements of opposite sign had been observed for several decades before the earthquake. After the earthquake, they revived and had great speed, but gradually slowed down to the previous rate.

One of the nodal planes of the mechanism of the focus of the earthquake was almost vertical and parallel to the coast, the other was almost horizontal. It is assumed that the earthquake could have been caused by a gently sloping overthrust of the insular flank onto the oceanic flank.

The earthquake was accompanied by a series of aftershocks, but there were not very many. The zone of the epicenters of the aftershocks, and possibly the source of the earthquake in general, were smaller than the source of the tsunami and the zone of noticeable change in relief, which had a length of 300 km. The causes of this discrepancy have so far not been elucidated.

A sizable tsunami rolled onto the coast of the Kii Peninsula and Shikoku Island. The tsunami was strongest on the east coast of Kii Strait, from Fukuro to Mio, where the rise of water was 6 m.

Iida et al. (1967): 20.XII; 19h19m; 33 N., 135.6 E.; 30 km; M=8.1, m=2.4.

Reference #150:

Lists 1,362 deaths, 11,661 houses destroyed, 1,451 houses washed away, 2,598 houses burned down.

Different Reports of Epicenters, Magnitudes and Effects

Latitude NLongitude EDepth (km)MagnitudeFatalities from

the EarthquakeHouses

Washed AwayHouses

DestroyedHouses

BurnedReference33135.6208.11326145111661259815033135.6308.114431451 41441433135.6308.115001151 797932.5134.5258.41997 4533135.6308.11362 1152 8.1 Mw 131433.123135.905158.3 Mw 13456, 13546