According to catastrophe modeling firm AIR Worldwide, on September 5 at 8:42 AM local time, a magnitude 7.6 earthquake struck a sparsely populated region of western Costa Rica approximately 150 km [94 miles] west of San José , the nation’s capital and largest city (approximate population 365,800 as of 2006). The earthquake, initially estimated at a magnitude of 7.9, occurred at a depth of 40 kilometers [25 miles].