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Estimating two-dimensional static stabilities and geomorphic settings of precariously balanced rocks from unconstrained digital photographs

  • The need to accurately document the spatiotemporal distribution of earthquake-generated strong ground motions is essential for evaluating the seismic vulnerability of sites of critical infrastructure. Understanding the threshold for maximum earthquake-induced ground motions at such sites provides valuable information to seismologists, earthquake engineers, local agencies, and policymakers when determining ground motion hazards of seismically sensitive infrastructures. In this context, fragile geologic features such as precariously balanced rocks (PBRs) serve as negative evidence for earthquake-induced ground motions and provide important physical constraints on the upper limits of ground motions. The three-dimensional (3D) shape of a PBR is a critical factor in determining its static stability and thus susceptibility to toppling during strong ground shaking events. Furthermore, the geomorphic settings of PBRs provide important controls on PBR exhumation histories that are interpreted from surface exposure dating methods. In thisThe need to accurately document the spatiotemporal distribution of earthquake-generated strong ground motions is essential for evaluating the seismic vulnerability of sites of critical infrastructure. Understanding the threshold for maximum earthquake-induced ground motions at such sites provides valuable information to seismologists, earthquake engineers, local agencies, and policymakers when determining ground motion hazards of seismically sensitive infrastructures. In this context, fragile geologic features such as precariously balanced rocks (PBRs) serve as negative evidence for earthquake-induced ground motions and provide important physical constraints on the upper limits of ground motions. The three-dimensional (3D) shape of a PBR is a critical factor in determining its static stability and thus susceptibility to toppling during strong ground shaking events. Furthermore, the geomorphic settings of PBRs provide important controls on PBR exhumation histories that are interpreted from surface exposure dating methods. In this paper, we present PBRslenderness, a MATLAB-based program that evaluates the two-dimensional (2D) static stabilities of PBRs from unconstrained digital photographs. The program's graphical user interface allows users to interactively digitize a PBR and calculates the 2D geometric parameters that define its static stability. A reproducibility study showed that our 2D calculations compare well against their counterparts that were computed in 3D (R-2 = 0.77-0.98 for 22 samples). A sensitivity study for single-user and multiuser digitization routines further confirmed the reproducibility of PBRslenderness estimates (coefficients of variation c(v) = 4.3%-6.5% for 100 runs; R-2 = 0.87-0.99 for 20 PBRs). We used PBRslenderness to analyze 261 PBRs in a low-seismicity setting to investigate the local geomorphic controls on PBR stability and preservation. PBRslenderness showed that a PBR's shape strongly controls its static stability and that there is no relationship between a PBR's stability and its geomorphic location in a drainage basin. However, the geomorphic settings of PBRs control their preservation potential by restricting their formation to hillslope gradients <40 degrees and the upper reaches of drainage basins. Such examples of our program's utility have led to its use in archival efforts of PBRs in southern California and Nevada, USA.show moreshow less

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Author details:David E. Haddad, Olaf Zielke, J. Ramon Arrowsmith, Matthew D. Purvance, Amanda G. Haddad, Angela LandgrafORCiDGND
DOI:https://doi.org/10.1130/GES00788.1
ISSN:1553-040X
Title of parent work (English):Geosphere
Publisher:American Institute of Physics
Place of publishing:Boulder
Publication type:Article
Language:English
Year of first publication:2012
Publication year:2012
Release date:2017/03/26
Volume:8
Issue:5
Number of pages:12
First page:1042
Last Page:1053
Funding institution:Southern California Earthquake Center (SCEC) Extreme Ground Motion Special Group; National Science Foundation (NSF) [EAR-0529922]; U.S. Geological Survey [07HQAG0008]; Arizona State University (ASU) Graduate and Professional Student Association; ASU Office of the Vice President of Research and Economic Affairs; ASU Graduate College; NSF
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Geowissenschaften
Peer review:Referiert
Institution name at the time of the publication:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Erd- und Umweltwissenschaften
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