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3.4 Disturbance related to ground fractures

Of the three principal sites of surface faulting or cracking (Granada Hills, Northridge-Reseda, and Potrero Canyon), only the Granada Hills are crossed by the precision leveling lines used in this study (Figure 12). Three routes traverse the Granada Hills faulting zone; 8 BMs locating within 500 m of the mapped zone of faulting [Hecker, et al., 1995]. None of the BMs located near the ground cracking are disturbed (Figure 13). BM 39 (EW4844), located in sediment 0.5 km north of the cracking, subsided by 13 cm, and BM 38 (AA3236), 2 km south of the cracking, is disturbed by 3 cm. The absence of any consistent offset of the elevation change profile across the Granada Hills faulting zone demonstrates that the faulting is superficial, a finding in accord with the conclusions of Hecker et al [1995]. If the fault slip extended to a depth of a few kilometers, most of these BMs would be displaced, and the elevation change would diminish with distance from the fault zone.

• Figure 12. Granada Hills. Damaged bench marks are shown as white circles and numbered as shown in Map 1. Gray lines indicate the modeled uplift contours and small black dots indicate ground cracking (Hecker et al., 1995).

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