Pliocene (ca. 3.5 Ma) removal of dense eclogitic material under the Sierra Nevada has been proposed from variations in the petrology and geochemistry of Neogene volcanic rocks and their entrained xenoliths from the southern Sierra. The replacement of eclogite by buoyant, warm asthenosphere is consistent with present-day seismologic and magnetotelluric observations made in the southern Sierra. A necessary consequence of replacing eclogite with peridotite is that mean surface elevations and gravitational potential energy both increase. An increase in potential energy should increase extensional strain rates in the area. If these forces are insuffi cient to signifi cantly alter Pacifi c-North American plate motion, then increased extensional strain rates in the vicinity of the Sierra must be accompanied by changes in the rate and style of deformation elsewhere. Changes in deformation in California and westernmost Nevada agree well with these predictions. Existing geologic evidence indicates that a period of rapid uplift along the Sierran crest of more than ~1 km occurred between 8 and 3 Ma, most likely as a consequence of removal of lower lithosphere. About this same time, extensional deformation was initiated within ~50 km of the eastern side of the Sierra (5-3 Ma), and regional shortening began to produce the California Coast Ranges (5-3 Ma). We suggest that these events were induced by the >1.2 × 10 12 N/m increase of gravitational potential energy generated by the Sierran uplift. Evidence for Pliocene uplift, adjoining crustal extension, and shortening in directly opposing parts of the Coast Ranges is found along nearly the entire length of the Sierra Nevada and implies that lithosphere was removed beneath all of the presentday mountain range. The uplifted area lies between two large, upper-mantle, high-Pwave-velocity bodies under the south end of the San Joaquin Valley and the north end of the Sacramento Valley. These high-velocity bodies plausibly represent the present position of material removed from the base of the crust. Lithospheric removal may also be responsible for shifting of the distribution of transform slip from the San Andreas Table 1) where estimates have been made of the timing of initial extension, the western edge of extension at ca. 5 Ma (thick purple line) and ca. 3 Ma (thick red line), the location of fl oras showing possible uplift (blue dots: T-Table Mountain and W-Webber Lake localities of Wolfe et al. [1998, 1997]), and the extent of tilted Miocene sedimentary rocks along the Sierra/ Great Valley margin (hatched area). The geology in the Sierra is shown in B (after Wakabayashi and Sawyer, 2000) along with the location of the ancestral Yuba River channel plotted in Figure 3 (thin red line) and the positions (bold letters) of other paleochannels plotted in Figure 3: M-Mokelumne River; S-Stanislaus River; and T-Tuolumne River. The position of the Gorda plate's southern edge relative to the Sierra at different times in the past lies along the green lines (from Atwater and Stock, 1998) assum...

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Abstract. Fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates, which are not necessarily parallel or equal. At the local scale of an individual fault, the shear plane and slip direction define the orientations of the local principal strain rate axes but not, in general, the local principal stress axes. At a large scale, the orientations of P and T axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress. The quantitative inversion of such fault slip data, however, provides direct constraints on the orientations and relative magnitudes of the global principal strain rates. To interpret the inversion solution as constraining the global principal stresses requires that (1) the fault slip pattern must have a characteristic symmetry no lower than orthorhombic; (2) the material must be mechanically isotropic; and (3) there must be a linear constitutive relationship between the global stress and the global strain rate. Isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity. Fault slip inversions, however, constrain the characteristics of a large-scale cataclastic flow, which is described by constitutive equations that are probably, but to an unknown degree, anisotropic and nonlinear. Such material behavior would not strictly satisfy the requirements for the stress interpretation. Thus, at the present state of knowledge, fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates.

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