Earthquake The earthquake hazard is most serious in Japan and the western USA, which form part of the Pacific seismic belt responsible for about 80 per cent of the world's earthquakes (Box 19.1). Nearly 90 per cent of the seismic activity of the continental USA occurs in Western Nevada and California, the latter state in particular being an area of pronounced immigration and population growth in recent dec- ades. Several major earthquakes affected California over the past century, including the 1960 and 1989 earthquakes in San Francisco that killed 700 and sixty-two people respectively. In the 1994 North- ridge LA earthquake fifty-seven people died, 60,000 housing units were destroyed and damage totalled $40,000 million. 3 Experts agreed that the main are question is when rather than whether another major earthquake will affect the area.