Abstract

Comparative elevation studies based on levelings in 1961, 1964, 1965, 1968, and 1969 show that the central Transverse Ranges of southern California sustained major elevation changes prior to the 1971 San Fernando earthquake. These changes are referred chiefly to bench mark Tidal 8, San Pedro, as invariant in elevation; they have been almost uniformly positive and generally episodic. Maximum uplift was recorded during the interval 1961–1964; it occurred south of Palmdale, about 28 km east-northeast of the 1971 epicenter, and measured 207 mm. Maximum values of uplift recorded along the main north-south level line through the central Transverse Ranges were 96 mm measured between 1961 and 1968, 13 km southwest of the epicenter, and 129 mm measured between 1964 and 1968, 30 km northwest of the epicenter. Uplift of 78 mm in reference to a control point 40 km northwest of Saugus was recorded 12 km west-northwest of the epicenter during the interval 1968–1969. The crustal movements recognized here are most simply interpreted as the product of continuing north-south contractional strain. Alternatively, the more episodic movements in particular may derive from dilatancy (inelastic volume increases) postulated to occur before earthquakes. Because the uplift near Palmdale has continued more or less independently of that to the south and west, it is probably associated with mechanically separable strain accumulation on the San Andreas fault.

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