A Caltech Library Service

Seismotectonics of an evolving intracontinental plate boundary, southeastern California

Unruh, Jeffrey and Hauksson, Egill (2009) Seismotectonics of an evolving intracontinental plate boundary, southeastern California. In: Late Cenozoic Structure and Evolution of the Great Basin-Sierra Nevada Transition. Special papers (Geological Society of America). No.447. Geological Society of America , Boulder, CO, pp. 351-372. ISBN 9780813724478.

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item:


An analysis of seismicity in the northern Mojave block, southern Walker Lane belt, and southern Sierra Nevada provides a detailed snapshot of the kinematics of active deformation within a young and probably evolving intracontinental plate boundary in eastern California. Earthquakes in this region were relocated using joint hypocentral inversion, double-difference, and waveform cross-correlation techniques. Groups of focal mechanisms were inverted for the components of a reduced deformation rate tensor, and the inversion results were synthesized in maps of the regional seismogenic deformation field. In general, seismogenic deformation in the Eastern California shear zone and Walker Lane belt is characterized by distributed simple shear and primarily accommodates northwest translation of the Sierra Nevada–Central Valley (Sierran) microplate relative to stable North America. Crustal thinning in the southern Walker Lane belt is subordinate to northwest-directed dextral shear and typically is associated with releasing geometries among dextral faults. There is no significant variation in strain geometry in the transition from the Eastern California shear zone to the Walker Lane belt across the Garlock fault; we interpret this to indicate that this structure is being sheared and rotated clockwise by distributed northwest dextral shear. In contrast, seismogenic deformation in the southeastern Sierra Nevada near latitude 36°N is characterized by horizontal elongation and locally by flattening, i.e., extension in two perpendicular horizontal directions. The transition from wrench tectonics in the southern Walker Lane to flattening in the High Sierra occurs across a 25- to 35-km-wide transtensional zone west of the Sierran range front. The elongation and flattening occur directly east of the “Isabella anomaly,” a high-velocity anomaly in the upper mantle interpreted to be lower Sierran lithosphere that is foundering or convectively descending into the asthenosphere. The seismogenic thinning of the southern Sierra may be related to thickening above the descending lithosphere to the west and/or may be driven by tensile buoyancy forces. The seismotectonics of this region may provide insights into the process by which the Walker Lane belt has progressively expanded westward into the Sierran microplate during late Cenozoic time.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Hauksson, Egill0000-0002-6834-5051
Additional Information:© 2009 The Geological Society of America. Accepted 21 July 2008. We performed this study under contract N68936-02-C-0207 from the U.S. Navy. We thank Frank Monastero, U.S. Navy Geothermal Program Office, for supporting this work and engaging us in many stimulating discussions about the seismotectonics of the study region. Hauksson also was supported by NEHRP/U.S. Geological Survey grants 04HQGR0052 and 05HQGR0040. Steve Thompson provided constructive criticism of an early draft of this paper. Comments by volume editor John Oldow and formal reviews by Basil Tikoff and an anonymous reviewer significantly improved the final version. This is contribution number 10,001 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
Group:Seismological Laboratory
Funding AgencyGrant Number
U.S. NavyN68936-02-C-0207
Subject Keywords:neotectonics, seismicity, seismotectonics, lithospheric dynamics
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Seismological Laboratory10,001
Series Name:Special papers (Geological Society of America)
Issue or Number:447
Record Number:CaltechAUTHORS:20150202-131243158
Persistent URL:
Official Citation:Unru h, J., and Hauksson, E., 2009, Seismotectonics of an evolving intracontinental plate boundary, southeastern California, in Oldow, J.S ., and Cashman, P.H., eds., Late Cenozoic Structure and Evolution of the Great Basin- Sierra Nevada Transition: Geological Society of America Special Paper 447, p. 351 - 372, doi: 10.1130/2009.2447(16)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54303
Deposited By: Tony Diaz
Deposited On:04 Feb 2015 04:11
Last Modified:10 Nov 2021 20:31

Repository Staff Only: item control page