It was interesting to read of processing mundane noise to produce an ultrasound image of the geology of Los Angeles. A big question in the state is the deep structure of San Francisco Bay. Clearly, the bay and the valleys extending to its northwest and southeast form a rift valley. But it’s difficult to observe faulting in the rocks because of the depth of sediment. Maybe the area could be probed ultrasonically.

Charles B. Warren
San Francisco, Calif.

From the Nature Index

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