FIGURE 6.1 San Francisco, on the morning of April 18, 1906. This famous photograph by Arnold Genthe shows Sacramento Street and the approaching fire in the distance. (Photograph courtesy of the Fine Arts Museums of San Francisco, Achenbach Foundation for Graphic Arts.)

its effects remained largely in the desert—but because it occurred in the south. The Loma Prieta quake had given seismologists important information about the San Andreas fault around San Francisco, but Landers provided a message to Los Angelenos, whose city's fate rests upon a network of underground faults that share with Northern California only the fundamental fact that all are part of the major fault system defining the boundary between the Pacific and North American plates.

Why does the occurrence of a quake many miles from Los Angeles carry a prophetic message for the nation's second-largest city? Will "The Big One" strike there or at San Francisco, or somewhere else along the hundreds of miles of faults throughout California? Will the Parkfield prediction pan out, and when the quake does arrive, will the unprecedented experimental effort devoted to that region pay off? What is happening underground during an earthquake, and why, and, most importantly, where and when? These questions all point to a bottom line that few would dispute, for from a successful methodology of earthquake prediction could come the conservation of billions of dollars and the survival of many people who otherwise might perish in these unavoidable natural disasters. And why unavoidable? The question



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