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A Google Earth™ image showing the principal zone of faulting (in red) near the the town of Healdsburg, overlain on a hillshade image from a LiDAR survey along the fault.

A new more detailed and higher resolution map of the Rodgers Creek Fault in Sonoma County, California, has been produced using aerial photography and hillshade imagery derived from LiDAR data (see Down in the Trenches…). "Bare-earth” imagery from LiDAR data allowed mapping of faulting-related landforms at a finer scale than possible previously, including identification of features hidden beneath trees and other vegetation.

The Rodgers Creek Fault, which lies east of the San Andreas Fault, is a main strand of the North American-Pacific Plate boundary north of San Francisco Bay. The two sides of the fault slip past each other at a rate of 6-10 mm/yr, and it has been estimated that there is a 33% chance of a M>=6.7 earthquake on the combined Rodgers Creek-Hayward fault system over the 30-year period 2014-2043.

New information that came to light as a result of this new map includes: 1) that the Rodgers Creek Fault extends about 17 km farther north than previously thought and flanks the east side of the town of Healdsburg; 2) identification of where the fault crosses the Santa Rosa Creek floodplain in central Santa Rosa; 3) identified parts of the fault zone that extend toward the Bennett Valley-Maacama Fault system to the east, and toward the Hayward Fault to the south beneath San Pablo Bay; and 4) an overall increase in the known width and complexity of the fault zone.

These new findings indicate a greater hazard than previously thought for the area from increased exposure to potential surface fault rupture and strong ground shaking .

- written by Lisa Wald, U.S. Geological Survey, July 16, 2018

A fault scarp in Santa Rosa can be seen as the gentle rise in the street.

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A creeping (slowly slipping) trace of the fault where it crosses an old road in the Healdsburg Ridge Open Space Preserve.

The Scientist Behind the Science

Suzanne Hecker.

Suzanne Hecker is a geologist with the USGS, where she studies the geologic record of large prehistoric earthquakes and the behavior of active faults. When not in the office or in the field, she enjoys leisurely outdoor pursuits and the pleasure of reading a good book.