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Rates and patterns of surface deformation from laser scanning following the South Napa earthquake, California

Stephen B. DeLong, James J. Lienkaemper, Alexandra J. Pickering and Nikita N. Avdievitch
Rates and patterns of surface deformation from laser scanning following the South Napa earthquake, California
Geosphere (Boulder, CO) (December 2015) 11 (6): 2015-2030

Abstract

The A.D. 2014 M6.0 South Napa earthquake, despite its moderate magnitude, caused significant damage to the Napa Valley in northern California (USA). Surface rupture occurred along several mapped and unmapped faults. Field observations following the earthquake indicated that the magnitude of postseismic surface slip was likely to approach or exceed the maximum coseismic surface slip and as such presented ongoing hazard to infrastructure. Using a laser scanner, we monitored postseismic deformation in three dimensions through time along 0.5 km of the main surface rupture. A key component of this study is the demonstration of proper alignment of repeat surveys using point cloud-based methods that minimize error imposed by both local survey errors and global navigation satellite system georeferencing errors. Using solid modeling of natural and cultural features, we quantify dextral postseismic displacement at several hundred points near the main fault trace. We also quantify total dextral displacement of initially straight cultural features. Total dextral displacement from both coseismic displacement and the first 2.5 d of postseismic displacement ranges from 0.22 to 0.29 m. This range increased to 0.33-0.42 m at 59 d post-earthquake. Furthermore, we estimate up to 0.15 m of vertical deformation during the first 2.5 d post-earthquake, which then increased by approximately 0.02 m at 59 d post-earthquake. This vertical deformation is not expressed as a distinct step or scarp at the fault trace but rather as a broad up-to-the-west zone of increasing elevation change spanning the fault trace over several tens of meters, challenging common notions about fault scarp development in strike-slip systems. Integrating these analyses provides three-dimensional mapping of surface deformation and identifies spatial variability in slip along the main fault trace that we attribute to distributed slip via subtle block rotation. These results indicate the benefits of laser scanner surveys along active faults and demonstrate that fine-scale variability in fault slip has been missed by traditional earthquake response methods.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 11
Serial Issue: 6
Title: Rates and patterns of surface deformation from laser scanning following the South Napa earthquake, California
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Pages: 2015-2030
Published: 201512
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 56
Accession Number: 2016-005543
Categories: Structural geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
N38°10'00" - N38°49'60", W122°40'00" - W122°02'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 201603
Program Name: USGSOPNon-USGS publications with USGS authors
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