Preliminary examination of the historic geodetic record has disclosed crustal uplift of 0.15 to 0.25 meter that apparently began around 1960 and has since grown to include at least 12,000 square kilometers of southern California. This uplift extends at least 150 kilometers west-northwestward along the San Andreas Fault from Cajon to Maricopa, southward from the San Andreas into the northern Transverse Ranges, and eastward from Lebec into and including much of western Mojave block. It seems to have grown spasmodically eastward from a center near the junction of the San Andreas and Garlock faults and has occurred largely within an area that has remained virtually aseismic since at least 1932. Although much of this area has been characterized by crustal mobility since at least the turn the century, the described uplift seems to be an unusually large and probably unique event superimposed the existing pattern of continuing deformation.
Discrepancies in sea surface topography based on comparisons between the results of steric leveling and repeated geodetic levelings have identified what is known as the ‘sea slope problem.’ This problem is actually twofold: (1) the sea surface relief based on steric leveling differs significantly from that based on geodetic leveling along several generally north‐south coasts, and (2) successively propagated levelings between several widely separated tide stations indicate that the stationary sea slope seemingly has been changing with time, whereas differenced sea level means between these stations indicate that the sea surface relief has remained virtually invariant during the same intervals. Reexamination of the three reported discrepancies between geodetically and sterically determined sea slopes indicates that the Australian example is based on leveling of a quality inappropriate to the comparison. The discrepancy developed along the Atlantic coast of the United States is limited to the reach between Portsmouth–Hampton Roads, Virginia, and Key West, Florida, where the accuracy of steric leveling may be especially vulnerable owing to the dynamic effects of the Gulf Stream. Reconsideration of the example along the Pacific coast of the United States indicates that the various discrepancies are due chiefly to intrasurvey movement and resultant distortion of geodetically defined height differences between tide stations. Agreement between the results of steric and geodetic leveling along tectonically inactive north‐south coasts devoid of strong boundary currents is generally good. This observation supports the conclusions (1) that any directionally dependent systematic error in geodetic leveling is measurably insignificant and (2) that where allowance is made for the possible effects of major boundary currents or intrasurvey movement during levelings between tide stations, the sea slope problem tends to vanish.
Introduction 1 Acknowledgments 3 Geologic framework 3 Historical deformation 3 Nontectonic deformation 3 Artificially induced deformation 3 Naturally induced deformation 4 Tectonic deformation 4 Vertical-control data 4 Errors in height determinations 5 Blunders 6 Systematic error 6 Random error 12 Errors associated with continuing crustal deformation-12 Errors associated with an inaccurately evaluated orthometric correction 13 Page The reconstruction 14 The Oxnard-Guadalupe line 17 The San Pedro-Bakersfield line 23 The Los Angeles-Riverside line 34 The Mojave-Barstow line 38 The San Diego-Barstow line 43 The San Diego-Arlington line 46 The Colton-Mecca line PLATE 1. Physiographic map showing major topographic features, naturally defined geologic provinces, and major faults identified with Quaternary displacement in southern California 2. Physiographic map of southern California, showing areas in which fluid extraction began before 1936 3. Map showing locations and names of bench marks used in the reconstruction of height changes, and principal routes and dates of leveling referred to in this report 4-9. Topography and height changes (A/i) with respect to bench mark Tidal 8 along: 4. The Oxnard-Guadalupe line 5. The San Pedro-Bakersfield line 6. The Los Angeles-Riverside and Mojave-Barstow lines 7. The San Diego-Barstow line 8. The San Diego-Arlington line 9. The Colton-Mecca line 10. Distribution of earthquakes in southern California and adjacent parts of northern Mexico of magnitude 5 for the period January 1, 1902-December 31, 1935, superimposed on contours of cumulative uplift developed during the epoch 1902.0-24.0 Any use of trade names and trademarks in this publication is for descriptive purposes only and does not constitute endorsement by the U.S. Geological Survey.
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