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Seismotectonics of an evolving intracontinental plate boundary, southeastern California

Jeffrey Unruh and Egill Hauksson
Seismotectonics of an evolving intracontinental plate boundary, southeastern California (in Late Cenozoic structure and evolution of the Great Basin-Sierra Nevada transition, John S. Oldow (editor) and Patricia H. Cashman (editor))
Special Paper - Geological Society of America (2009) 447: 351-372

Abstract

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 degrees 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.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 447
Title: Seismotectonics of an evolving intracontinental plate boundary, southeastern California
Title: Late Cenozoic structure and evolution of the Great Basin-Sierra Nevada transition
Author(s): Unruh, JeffreyHauksson, Egill
Author(s): Oldow, John S.editor
Author(s): Cashman, Patricia H.editor
Affiliation: William Lettis and Associates, Walnut Creek, CA, United States
Affiliation: University of Texas at Dallas, Department of Geosciences, Richardson, TX, United States
Pages: 351-372
Published: 2009
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 40
Accession Number: 2009-079388
Categories: SeismologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 3 tables, sketch maps
N34°45'00" - N36°49'60", W118°30'00" - W116°15'00"
Secondary Affiliation: University of Nevada, USA, United StatesCalifornia Institute of Technology, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200942
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