LOS ANGELES - A recently mapped, still-active fault line that snakes beneath downtown Los Angeles is capable of generating major earthquakes (news - web sites), but only about once every 2,000 years, according to a new study. At least four earthquakes of estimated magnitudes 7.2 to 7.5 have struck over the last 11,000 years on the Puente Hills fault, which was first mapped just four years ago. A segment of the fault last ruptured in 1987 with a magnitude-6 earthquake (news - web sites). The study is the first to show how often and with how much punch large quakes...