Scientific Investigations Report 2006–5218
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5218
These interferograms reveal regional (valleywide) and localized land subsidence and uplift patterns. The most obvious deformation feature is the northwest subsidence bowl and its proximity to the Eglington fault (figs. 3 and 7; Amelung and others, 1999; Bell and others, 2000). Deformation is persistent along the north-south axis of the valley, but the remaining subsidence bowls are less defined than the northwest bowl (fig. 7). Generally, individual interferograms that predominately span months of increased pumpage (May–September) have patterns dominated by land subsidence (interferograms 2, 3, 15, 23, 27, 28, 29, 41, and 42; table 1) and interferograms that predominately span months of decreased pumpage or artificial recharge have more complex deformation patterns that include regional or local uplift (Hoffmann and others, 2001; Hoffmann, 2003). For interferograms that span mostly months of decreased pumpage, 8 predominantly have uplift (interferograms 6, 8, 18, 19, 35, 36, 38, and 40), 6 predominantly have subsidence (interferograms 4, 11, 12, 14, 34, and 44), and 17 have both subsidence and uplift (interferograms 1, 5, 7, 9, 10, 13, 16, 17, 20, 21, 22, 24, 31, 32, 33, 37, and 39). Generally, land uplift does not occur within the northwestern subsidence bowl. Recurring, localized deformation features (fig. 7) generally appear in the northeastern part of the valley and are more easily identified on multicolor interferograms than three-color interferograms. The stacked interferogram shows that from September 8, 1992 to December 10, 1999, the predominant type of vertical displacement was subsidence.
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