Surface rupturing during the February 9, 1971, San Fernando earthquake occurred chiefly along known faults than can be included in the Santa Susana–Sierra Madre fault zone. Most of the surface displacements were associated with known faults that are shown only on unpublished maps. Because the Metropolitan Water District (MWD) has tunnels under construction and others proposed in this area, most of the faults had been studied in detail to determine their respective effects upon groundwater distribution and tunnel construction. These surface breaks and associated faults are described.
The area that includes surface ruptures accompanying the San Fernando earthquake extends 19 km (12 mi) from east to west and 6 km (4 mi) from north to south. The largest single vertical displacement observed within this area was 1.5 m (5.0 ft) on the Lakeview thrust fault scarp in Oliver Canyon, 7 km (4.4 mi) east of San Fernando. The maximum cumulative uplift, from MWD surveys of the San Fernando Tunnel north of the Sylmar fault, was 2.3 m (7.5 ft). The maximum horizontal displacement, left-lateral, was 1.9 m (6.2 ft) on the Sylmar fault. The overall north-south shortening was 2.3 m (7.5 ft).