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The uplift pattern formed an elongated (and lopsided) dome over the part of the fault that experienced the most slip in the earthquake. On the north side of this dome, the ground surface tilted towards the north-northeast. On the south side of the dome, the ground surface tilted south-southwestward. The steepest tilting occured along the northeastern edge of the Santa Susana mountain range.
In this area, the ground tilts were about 5 cm per kilometer, which also happens to be the normal engineering grade for aqueduct design. So, in this situation, the existing water systems were tilted back against their design grade by an amount about equal to that grade. Had the earthquake been larger, or had the slip come up closer to the ground surface (as happened in the 1971 earthquake), the water systems would have been even more severely affected.
The diagram and map below illustrate how the ground tilting in the Northridge
earthquake affected these systems.
To illustrate how the ground surface was deformed in the Northridge
earthquake, the following image shows the topography with contours of
vertical displacement overlain (in yellow). The upper panel shows a
vertically exaggerated rendition of how the ground surface was pushed
up into a dome shape. The mesh on this upper panel and contours in
the map view on the lower panel together help in registering
locations on the upper and lower images.
For more data on vertical deformation in the Northridge earthquake, please
go to the 'level' page., or to our more recent
report.
For more information, contact
Ken Hudnut at hudnut@seismo.gps.caltech.edu
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