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  • 1
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    Surface Slip during Large Owens Valley Earthquakes (2016)
    Wiley
    Details
    Publication Date: 2016-01-10
    Description: The 1872 Owens Valley earthquake is the third largest known historical earthquake in California. Relatively sparse field data and a complex rupture trace, however, inhibited attempts to fully resolve the slip distribution and reconcile the total moment release. We present a new, comprehensive record of surface slip based on lidar and field investigation, documenting 162 new measurements of laterally and vertically displaced landforms for 1872 and prehistoric Owens Valley earthquakes. Our lidar analysis uses a newly developed analytical tool to measure fault slip based on cross-correlation of sub-linear topographic features and produce a uniquely shaped probability density function (PDF) for each measurement. Stacking PDFs along strike to form cumulative offset probability distribution plots (COPDs) highlights common values corresponding to single- and multiple-event displacements. Lateral offsets for 1872 vary systematically from ∼1.0–6.0 m and average 3.3 ± 1.1 m. Vertical offsets are predominantly east-side down between ∼0.1–2.4 m, with a mean of 0.8 ± 0.5 m. The average lateral-to-vertical ratio compiled at specific sites is ∼6:1. Summing displacements across sub-parallel, overlapping ruptures implies a maximum of 7–11 m and net average of 4.4 ± 1.5 m, corresponding to a geologic M w ∼7.5 for the 1872 event. We attribute progressively higher-offset lateral COPD peaks at 7.1 ± 2.0 m, 12.8 ± 1.5 m, and 16.6 ± 1.4 m to three earlier large surface ruptures. Evaluating cumulative displacements in context with previously dated landforms in Owens Valley suggests relatively modest rates of fault slip, averaging between ∼0.6–1.6 mm/yr (1σ) over the late Quaternary. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Sub-Patch Roughness in Earthquake Rupture Investigations (2016)
    Wiley
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    Publication Date: 2016-02-14
    Description: Fault geometric complexities exhibit fractal characteristics over a wide range of spatial scales ( 〈µm to 〉km ) and strongly affect the rupture process at corresponding scales. Numerical rupture simulations provide a framework to quantitatively investigate the relationship between a fault's roughness and its seismic characteristics. Fault discretization however introduces an artificial lower limit to roughness. Individual fault patches are planar and sub-patch roughness –roughness at spatial scales below fault-patch size– is not incorporated. Does negligence of sub-patch roughness measurably affect the outcome of earthquake rupture simulations? We approach this question with a numerical parameter space investigation and demonstrate that sub-patch roughness significantly modifies the slip-strain relationship –a fundamental aspect of dislocation theory. Faults with sub-patch roughness induce less strain than their planar-fault equivalents at distances beyond the length of a slipping fault. We further provide regression functions that characterize the stochastic effect sub-patch roughness.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Slip in the 1857 and earlier large earthquakes along the Carrizo Plain, San Andreas Fault (2010)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2010-01-23
    Description: The moment magnitude (Mw) 7.9 Fort Tejon earthquake of 1857, with a approximately 350-kilometer-long surface rupture, was the most recent major earthquake along the south-central San Andreas Fault, California. Based on previous measurements of its surface slip distribution, rupture along the approximately 60-kilometer-long Carrizo segment was thought to control the recurrence of 1857-like earthquakes. New high-resolution topographic data show that the average slip along the Carrizo segment during the 1857 event was 5.3 +/- 1.4 meters, eliminating the core assumption for a linkage between Carrizo segment rupture and recurrence of major earthquakes along the south-central San Andreas Fault. Earthquake slip along the Carrizo segment may recur in earthquake clusters with cumulative slip of approximately 5 meters.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zielke, Olaf -- Arrowsmith, J Ramon -- Grant Ludwig, Lisa -- Akciz, Sinan O -- New York, N.Y. -- Science. 2010 Feb 26;327(5969):1119-22. doi: 10.1126/science.1182781. Epub 2010 Jan 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA. olaf.zielke@asu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20093436" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Climate-modulated channel incision and rupture history of the San Andreas Fault in the Carrizo Plain (2010)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2010-01-23
    Description: The spatial and temporal distribution of fault slip is a critical parameter in earthquake source models. Previous geomorphic and geologic studies of channel offset along the Carrizo section of the south central San Andreas Fault assumed that channels form more frequently than earthquakes occur and suggested that repeated large-slip earthquakes similar to the 1857 Fort Tejon earthquake illustrate typical fault behavior. We found that offset channels in the Carrizo Plain incised less frequently than they were offset by earthquakes. Channels have been offset by successive earthquakes with variable slip since ~1400. This nonuniform slip history reveals a more complex rupture history than previously assumed for the structurally simplest section of the San Andreas Fault.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Grant Ludwig, Lisa -- Akciz, Sinan O -- Noriega, Gabriela R -- Zielke, Olaf -- Arrowsmith, J Ramon -- New York, N.Y. -- Science. 2010 Feb 26;327(5969):1117-9. doi: 10.1126/science.1182837. Epub 2010 Jan 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Program in Public Health and California Institute for Hazards Research, University of California, Irvine, CA 92697, USA. lgrant@uci.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20093439" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Differentiating simple and composite tectonic landscapes using numerical fault-slip modeling with an example from the south-central Alborz Mountains, Iran (2013)
    Wiley
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    Publication Date: 2013-07-14
    Description: [1]  The tectonically driven growth of mountains reflects the characteristics of the underlying fault systems and the applied tectonic forces. Over time, fault networks might be relatively static, but stress conditions could change and result in variations in fault slip orientation. Such a tectonic landscape would transition from a “simple” to a “composite” state: the topography of simple landscapes is correlated with a single set of tectonic boundary conditions, while composite landscapes contain inherited topography due to earlier deformation under different boundary conditions. We use fault-interaction modelling to compare vertical displacement fields with topographic metrics to differentiate the two types of landscapes. By successively rotatingthe axis of maximum horizontal stress, we produce a suite of vertical displacement fields for comparison with real landscapes. We apply this model to a transpressional duplex in the south-central Alborz Mountains of Iran, where NW-oriented compression was superseded by neotectonic NE compression. The consistency between the modeled displacement field and real landforms indicates that the duplex-topography is mostly compatible with the modern boundary conditions, but might include a small remnant from the earlier deformation phase. Our approach is applicable for various tectonic settings and represents an approach to identify the changing boundary conditions that produce composite landscapes. It may be particularly useful for identifying changes that occurred in regions where river profiles may no longer record a signal of the change, or where the spatial pattern of upliftis complex.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Fault roughness and strength heterogeneity control earthquake size and stress drop (2017)
    Wiley
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    Publication Date: 2017-01-14
    Description: An earthquake's stress drop is related to the frictional breakdown during sliding and constitutes a fundamental quantity of the rupture process. High-speed laboratory friction experiments that emulate the rupture process imply stress drop values that greatly exceed those commonly reported for natural earthquakes. We hypothesize that this stress drop discrepancy is due to fault-surface roughness and strength heterogeneity: An earthquake's moment release and its recurrence probability depend not only on stress drop and rupture dimension, but also on the geometric roughness of the ruptured fault and the location of failing strength asperities along it. Using large-scale numerical simulations for earthquake ruptures under varying roughness and strength conditions, we verify our hypothesis, showing that smoother faults may generate larger earthquakes than rougher faults under identical tectonic loading conditions. We further discuss the potential impact of fault roughness on earthquake recurrence probability. This finding provides important information, also for seismic hazard analysis.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Über die Eschenwollschildlaus, Fonscolombea fraxini (Kalt.) Ckll. (Hem. Cocc.), und die standörtlichen Befallsverhältnisse bei der Esche, Fraxinus excelsior L. (1942)
    In:  Arb. Biol. Reichsanst. 23: 293-386
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    Publication Date: 1942
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  • 8
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    Estimating two-dimensional static stabilities and geomorphic settings of precariously balanced rocks from unconstrained digital photographs (2012)
    Geological Society of America (GSA)
    In: Geosphere
    Details
    Publication Date: 2012-10-01
    Description: 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 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° 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.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 9
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    Validation of meter-scale surface faulting offset measurements from high-resolution topographic data (2015)
    Geological Society of America (GSA)
    In: Geosphere
    Details
    Publication Date: 2015-12-02
    Description: Studies of active fault zones have flourished with the availability of high-resolution topographic data, particularly where airborne light detection and ranging (lidar) and structure from motion (SfM) data sets provide a means to remotely analyze submeter-scale fault geomorphology. To determine surface offset at a point along a strike-slip earthquake rupture, geomorphic features (e.g., stream channels) are measured days to centuries after the event. Analysis of these and cumulatively offset features produces offset distributions for successive earthquakes that are used to understand earthquake rupture behavior. As researchers expand studies to more varied terrain types, climates, and vegetation regimes, there is an increasing need to standardize and uniformly validate measurements of tectonically displaced geomorphic features. A recently compiled catalog of nearly 5000 earthquake offsets across a range of measurement and reporting styles provides insight into quality rating and uncertainty trends from which we formulate best-practice and reporting recommendations for remote studies. In addition, a series of public and beginner-level studies validate the remote methodology for a number of tools and emphasize considerations to enhance measurement accuracy and precision for beginners and professionals. Our investigation revealed that (1) standardizing remote measurement methods and reporting quality rating schemes is essential for the utility and repeatability of fault-offset measurements; (2) measurement discrepancies often involve misinterpretation of the offset geomorphic feature and are a function of the investigator’s experience; (3) comparison of measurements made by a single investigator in different climatic regions reveals systematic differences in measurement uncertainties attributable to variation in feature preservation; (4) measuring more components of a displaced geomorphic landform produces more consistently repeatable estimates of offset; and (5) inadequate understanding of pre-event morphology and post-event modifications represents a greater epistemic limitation than the aleatoric limitations of the measurement process.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 10
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    Three-Dimensional Investigation of a 5 m Deflected Swale along the San Andreas Fault in the Carrizo Plain (2014)
    Seismological Society of America (SSA)
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    Publication Date: 2014-12-05
    Description: Topographic maps produced from Light Detection and Ranging (LiDAR) data are useful for paleoseismic and neotectonic research because they provide submeter representation of faulting-related surface features. Offset measurements of geomorphic features, made in the field or on a remotely sensed imagery, commonly assume a straight or smooth (i.e., undeflected) pre-earthquake geometry. Here, we present results from investigation of an ~20 cm deep and 〉5 m wide swale with a sharp bend along the San Andreas fault (SAF) at the Bidart fan site in the Carrizo Plain, California. From analysis of LiDAR topography images and field measurements, the swale was initially interpreted as a channel tectonically offset ~4.7 m. Our observations from exposures in four backhoe excavations and 25 hand-dug trenchettes show that even though a sharp bend in the swale coincides with the trace of the A.D. 1857 fault rupture, the swale formed after the 1857 earthquake and was not tectonically offset. Subtle fractures observed within a surficial gravel unit overlying the 1857 rupture trace are similar to fractures previously documented at the Phelan fan and LY4 paleoseismic sites 3 and 35 km northwest of Bidart fan, respectively. Collectively, the fractures suggest that a post-1857 moderate-magnitude earthquake caused ground cracking in the Carrizo and Cholame stretches of the SAF. Our observations emphasize the importance of excavation at key locations to validate remote and ground-based measurements, and we advocate more geomorphic characterization for each site if excavation is not possible. Online Material: Figures of trench logs.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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