This subject was of urgent importance but had built-in difficulties in the observation of environments in large cities. The January 17, 1995, Kobe earthquake was representative of an inland earthquake occurring in a semi-metropolitan area and resulted in a tremendous disaster far beyond our expectations.

Throughout the previous period, seismic activity in and around the Japanese islands had been rather calm. No destructive earthquake had occurred for 50 years (Fig. 1). Most that did occur since the start of the earthquake prediction plan were in rather isolated areas; the exception was the recent Kobe earthquake, which struck the center of a densely populated area. Under these circumstances, the Seventh Plan started in 1994. In addition to the continuation of basic observations, the concept of the assessment of earthquake potential was incorporated with the plan. The target is large earthquakes occurring along plate boundaries and in inland areas. The intention is to enhance the accuracy of long-term prediction. The concept of “earthquake cycles” is well accepted and supported by a persuasive data set. Historical records, trench study of active faults, and geodetic survey data accumulated over 100 years give clear evidence for repetition of large earthquakes in such areas as along the Nankai trough. Another noteworthy aspect of the Seventh Plan is the disposition of GPS (Global Positioning System) observation sites throughout the Islands. Collection of real-time data from about 300 sites will drastically change the concept of crustal deformation observation in the earthquake prediction program in Japan.

FIG. 1. Locations of destructive earthquakes in and around the Japanese islands since 1948. Most occurred in the sea area.