Water pressure gauge in the city of Santa Barbara from June 29, 1925. Note the jitter caused by foreshocks beginning at 3:27 AM (top middle of image) and continuing up to 6:42 AM (lower right of image). At 6:42 AM, the water pressure drops to nearly zero due to breaking of water mains in the earthquake.

This image was scanned from the Bulletin of the Seismological Society of America, v. 15, December, 1925.