The Eastern California Shear Zone as the northward extension of the southern San Andreas Fault

Journal of Geophysical Research B: Solid Earth
By: , and 

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Abstract

Cluster analysis offers an agnostic way to organize and explore features of the current GPS velocity field without reference to geologic information or physical models using information only contained in the velocity field itself. We have used cluster analysis of the Southern California Global Positioning System (GPS) velocity field to determine the partitioning of Pacific-North America relative motion onto major regional faults. Our results indicate the large-scale kinematics of the region is best described with two boundaries of high velocity gradient, one centered on the Coachella section of the San Andreas Fault and the Eastern California Shear Zone and the other defined by the San Jacinto Fault south of Cajon Pass and the San Andreas Fault farther north. The ~120 km long strand of the San Andreas between Cajon Pass and Coachella Valley (often termed the San Bernardino and San Gorgonio sections) is thus currently of secondary importance and carries lesser amounts of slip over most or all of its length. We show these first order results are present in maps of the smoothed GPS velocity field itself. They are also generally consistent with currently available, loosely bounded geologic and geodetic fault slip rate estimates that alone do not provide useful constraints on the large-scale partitioning we show here. Our analysis does not preclude the existence of smaller blocks and more block boundaries in Southern California. However, attempts to identify smaller blocks along and adjacent to the San Gorgonio section were not successful.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The Eastern California Shear Zone as the northward extension of the southern San Andreas Fault
Series title Journal of Geophysical Research B: Solid Earth
DOI 10.1002/2015JB012678
Volume 121
Issue 4
Year Published 2016
Language English
Publisher American Geophysical Union
Publisher location Washington, D.C.
Contributing office(s) Earthquake Science Center
First page 2904
Last page 2914
Country United States
Other Geospatial Eastern California Shear Zone
Online Only (Y/N) N
Additional Online Files (Y/N) N