An assessment of the accuracy of the geodetic measurements that define the southern California uplift

Abstract

Examination of the charge that the geodetic measurements which define the southern California uplift are seriously flawed by height-dependent systematic errors indicates that this charge is unfounded. Our review of those factors designed to minimize the effects of rod error shows that systematic errors attributable to rod miscalibration are trivial and would tend to cancel during the particularly pertinent period 1955–1965. Comparisons between the results of measurements in which the correlation between topography and signal is generally poor reveal large aseismic tilts in a number of places within and around the margins of the uplift. Especially significant in this context are the results of preuplift and postuplift levelings over routes characterized by diverse length, topography, and atmospheric conditions that produce closely matching, temporally equivalent heights for a representative bench mark within the uplift. Statistical analyses of the short-wavelength components of uplift signal and elevation along a frequently repeated survey line indicate variable correlations between the two. However, the spatial and temporal patterns of these correlations are inconsistent with their attribution to height-dependent systematic errors. Statistically significant short-wavelength correlations along this survey line are reasonably explained in part as due to real movement associated with differentially subsiding bench marks, and there is a strong likelihood that this movement tends to dominate many of the correlations.