(3)The Fukui Earthquake (June 28, 1948, M 7.1)


This earthquake occurred in a shallow land location, and its source region extended from the central to the eastern section of the Fukui Plain (Hukui Heiya). Seismic intensity 6 in JMA scale was observed in Fukui City (Hukui City) (Fig.6-20). Houses were totally collapsed in many settled areas of the Fukui Plain, which has broad stretches of soft ground (Fig.6-21). The earthquake caused 3,769 fatalities and the total collapsed of about 36,000 houses, however, this damage was limited to the Fukui Plain and surrounding areas (Fig.6-22). In addition, trains were derailed and overturned and there was large damage to civil engineering structures such as structural damage relating to railroads, roads, and rivers. Fires broke out in Fukui City and other locations throughout the Fukui Plain, destroying more than 3,800 houses.

Seismic intensity 6 in JMA scale was observed for this earthquake in the central part of the Fukui Plain and other areas close to the focal region. Because of the exceptionally severe damage caused by the collapsed houses, the Japan Meteorological Agency enacted a seismic intensity scale of 7. At this level, more than 30% of houses must collapse, and there must be landslides, ground fissures faults. This earthquake was ruled at a seismic intensity of 7 since more than 30% of the houses throughout the central and northern areas of the Fukui Plain collapsed. The Fukui Earthquake occurred directly beneath a modern city and spread through the soft ground. It is widely recognized that an earthquake of this type will cause an enormous amount of damage in a comparatively limited area.

No visible slip of the earth occurred as a result of this earthquake, but geodetic survey showed displacement at the surface in the eastern Fukui Plain caused by a fault with a strike of north-northwest to south-southeast direction. This was left-lateral strike-slip, and caused a rather extensive upheaval of the earth of about 70 cm in the east. In the west, the slip reached a maximum of about 2 m to south.

As shown in Fig.6-23, the number of perceptible and imperceptible aftershocks decayed. The largest aftershock (M 5.8) occurred six minutes after the main shock.