Detailed mapping and rupture implications of the 1 km releasing bend in the Rodgers Creek Fault at Santa Rosa, northern California

Bulletin of the Seismological Society of America
By: , and 

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Abstract

Airborne light detection and ranging (lidar) topography reveals for the first time the trace of the Rodgers Creek fault (RCF) through the center of Santa Rosa, the largest city in the northern San Francisco Bay area. Vertical deformation of the Santa Rosa Creek floodplain expresses a composite pull‐apart basin beneath the urban cover that is part of a broader 1‐km‐wide right‐releasing bend in the fault. High‐resolution geophysical data illuminate subsurface conditions that may be responsible for the complex pattern of surface faulting, as well as for the distribution of seismicity and possibly for creep behavior. We identify a dense, magnetic basement body bounded by the RCF beneath Santa Rosa that we interpret as a strong asperity, likely part of a larger locked patch of the fault to the south. A local increase in frictional resistance associated with the basement body appears to explain (1) distributed fault‐normal extension above where the RCF intersects the body; (2) earthquake activity around the northern end of the body, notably the 1969 ML 5.6 and 5.7 events and aftershocks; and (3) creep rates on the RCF that are higher to the north of Santa Rosa than to the south. There is a significant probability of a major earthquake on the RCF in the coming decades, and earthquakes associated with the proposed asperity have the potential to release seismic energy into the Cotati basin beneath Santa Rosa, already known from damaging historical earthquakes to produce amplified ground shaking.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Detailed mapping and rupture implications of the 1 km releasing bend in the Rodgers Creek Fault at Santa Rosa, northern California
Series title Bulletin of the Seismological Society of America
DOI 10.1785/0120150152
Volume 106
Issue 2
Year Published 2016
Language English
Publisher Seismological Society of America
Contributing office(s) Earthquake Science Center
Description 20 p.
First page 575
Last page 594
Country United States
State California
City Santa Rosa
Online Only (Y/N) N
Additional Online Files (Y/N) N