The records of the Richmond Quarry blast of August 16, 1934, indicate that the speed of longitudinal waves in the Franciscan formation of the San Francisco Bay region is 4.3 km/sec. The speed of transverse waves in the same medium is very probably 2.4 km/sec. The speed in the underlying medium is 5.4 km/sec. for the longitudinal waves and possibly 3.1 km/sec. for the transverse waves. The medium may therefore be identified as granite, which was to be expected from geological considerations.

The thickness of the Franciscan formation in the region as computed from data given by this blast is about one kilometer.

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