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  • 1
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    Paleoseismology of the Xorxol Segment of the Central Altyn Tagh Fault, Xinjiang, China (2006)
    INGV
    Details
    Publication Date: 2021-01-11
    Description: Although the Altyn Tagh Fault (ATF) is thought to play a key role in accommodating India-Eurasian convergence, little is known about its earthquake history. Studies of this strike-slip fault are important for interpretation of the role of faulting versus distributed deformation in the accommodation of the India- Eurasia collision. In addition, the 〉 1200 km long fault represents one of the most important and exemplary intracontinental strike-slip faults in the world. We mapped fault trace geometry and interpreted paleoseismic trench exposures to characterize the seismogenic behavior of the ATF. We identified 2 geometric segment boundaries in a 270 km long reach of the central ATF. These boundaries define the westernmost Wuzhunxiao, the Central Pingding, and the easternmost Xorxol (also written as Suekuli or Suo erkuli) segments. In this paper, we present the results from the Camel paleoseismic site along the Xorxol Segment at 91.759°E, 38.919°N. There evidence for the last two earthquakes is clear and 14C dates from layers exposed in the excavation bracket their ages. The most recent earthquake occurred between 1456 and 1775 cal A.D. and the penultimate event was between 60 and 980 cal A.D. Combining the Camel interpretations with our published results for the central ATF, we conclude that multiple earthquakes with shorter rupture lengths (?? 50 km) rather than complete rupture of the Xorxol Segment better explain the paleoseismic data. We found 2-3 earthquakes in the last 2-3 kyr. When coupled with typical amounts of slip per event (5-10 m), the recurrence times are tentatively consistent with 1-2 cm/yr slip rates. This result favors models that consider the broader distribution of collisional deformation, rather than those with northward motion of India into Asia absorbed along a few faults bounding rigid blocks.
    Description: Published
    Description: JCR Journal
    Description: open
    Keywords: paleoseismology ; Altyn Tagh Fault ; strike-slip faults ; India-Eurasia collision ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 1161909 bytes
    Format: application/pdf
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  • 2
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    Surface rupture of the 1911 Kebin (Chon-Kemin) earthquake, Northern Tien Shan, Kyrgyzstan (2016)
    Geological Society (of London)
    Details
    Publication Date: 2016-07-22
    Description: The 1911 Chon–Kemin (Kebin) earthquake culminated c. 30 years of remarkable earthquakes in the northern Tien Shan (Kyrgyzstan and Kazakhstan). Building on prior mapping of the event, we traced its rupture in the field and measured more than 50 offset landforms. Cumulative fault rupture length is 〉155–195 km along 13 fault patches comprising six sections. The patches are separated by changes of dip magnitude or dip direction, or by 4–10 km-wide stepovers. One 〈40 km section overlaps and is parallel to the main north-dipping rupture but is 7 km north and dips opposite (south). Both ends of the rupture are along mountain front thrust faults demonstrating late Quaternary activity. We computed the moment from each fault patch using the surface fault traces, dip inferred from the traces, 20 km seismogenic thickness, rigidity of 3.3 x 10 10 N m –2 and dip slip converted from our observations of the largely reverse sense of motion vertical offsets. The discontinuous patches with c. 3–4 m average slip and peak slip of 〈14 m yield a seismic moment of 4.6 x 10 20 Nm ( M w 7.78) to 7.4 x 10 20 Nm ( M w 7.91). The majority of moment was released along the inner eastern rupture segments. This geological moment is lower by a factor of 1.5 from that determined from teleseismic data.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 3
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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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  • 4
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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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  • 5
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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)
    Details
    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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  • 6
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    Analysis of Seismic Activity near Theodore Roosevelt Dam, Arizona, during the Occupation of the EarthScope/USArray Transportable Array (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-11-08
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 7
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    Rapid mapping of ultrafine fault zone topography with structure from motion (2014)
    Geological Society of America (GSA)
    In: Geosphere
    Details
    Publication Date: 2014-10-01
    Description: Structure from Motion (SfM) generates high-resolution topography and coregistered texture (color) from an unstructured set of overlapping photographs taken from varying viewpoints, overcoming many of the cost, time, and logistical limitations of Light Detection and Ranging (LiDAR) and other topographic surveying methods. This paper provides the first investigation of SfM as a tool for mapping fault zone topography in areas of sparse or low-lying vegetation. First, we present a simple, affordable SfM workflow, based on an unmanned helium balloon or motorized glider, an inexpensive camera, and semiautomated software. Second, we illustrate the system at two sites on southern California faults covered by existing airborne or terrestrial LiDAR, enabling a comparative assessment of SfM topography resolution and precision. At the first site, an ~0.1 km 2 alluvial fan on the San Andreas fault, a colored point cloud of density mostly 〉700 points/m 2 and a 3 cm digital elevation model (DEM) and orthophoto were produced from 233 photos collected ~50 m above ground level. When a few global positioning system ground control points are incorporated, closest point vertical distances to the much sparser (~4 points/m 2 ) airborne LiDAR point cloud are mostly 〈3 cm. The second site spans an ~1 km section of the 1992 Landers earthquake scarp. A colored point cloud of density mostly 〉530 points/m 2 and a 2 cm DEM and orthophoto were produced from 450 photos taken from ~60 m above ground level. Closest point vertical distances to existing terrestrial LiDAR data of comparable density are mostly 〈6 cm. Each SfM survey took ~2 h to complete and several hours to generate the scene topography and texture. SfM greatly facilitates the imaging of subtle geomorphic offsets related to past earthquakes as well as rapid response mapping or long-term monitoring of faulted landscapes.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Applications of airborne and terrestrial laser scanning to paleoseismology (2012)
    Geological Society of America (GSA)
    In: Geosphere
    Details
    Publication Date: 2012-08-01
    Description: Paleoseismic investigations aim to document past earthquake characteristics such as rupture location, frequency, distribution of slip, and ground shaking intensity—critical parameters for improved understanding of earthquake processes and refined earthquake forecasts. These investigations increasingly rely on high-resolution (〈1 m) digital elevation models (DEMs) to measure earthquake-related ground deformation and perform process-oriented analyses. Three case studies demonstrate airborne and terrestrial laser scanning (ALS and TLS) for paleoseismic research. Case 1 illustrates rapid production of accurate, high-resolution, and georeferenced three-dimensional (3D) orthophotographs of stratigraphic and fault relationships in trench exposures. TLS scans reduced the preparation time of the trench and provided 3D visualization and reconstruction of strata, contacts, and permanent digital archival of the trench. Case 2 illustrates quantification of fault scarp degradation rates using repeat topographic surveys. The topographic surveys of the scarps formed in the 1992 Landers (California) earthquake documented the centimeter-scale erosional landforms developed by repeated winter storm-driven erosion, particularly in narrow channels crossing the surface rupture. Vertical and headward incision rates of channels were as much as ~6.25 cm/yr and ~62.5 cm/yr, respectively. Case 3 illustrates characterization of the 3D shape and geomorphic setting of precariously balanced rocks (PBRs) that serve as negative indicators for strong ground motions. Landscape morphometry computed from ALS-derived DEMs showed that PBRs are preserved on hillslope angles between 10° and 40° and contributing areas (per unit contour length) between 5 and 30 m 2 /m. This situation refines interpretations of PBR exhumation rates and thus their effectiveness as paleoseismometers. Given that earthquakes disrupt Earth's surface at centimeter to meter scales and that depositional and erosional responses typically operate on similar scales, ALS and TLS provide the absolute measurement capability sufficient to characterize these changes in challenging geometric arrangements, and thus demonstrate their value as effective analytical tools in paleoseismology.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 9
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    Geometry and Quaternary slip behavior of the San Juan de los Planes and Saltito fault zones, Baja California Sur, Mexico: Characterization of rift-margin normal faults (2013)
    Geological Society of America (GSA)
    In: Geosphere
    Details
    Publication Date: 2013-06-01
    Description: An array of north-striking, left-stepping, active normal faults cuts the southwest margin of the Gulf of California and across the southern tip of the Baja California peninsula. This is the gulf margin fault system of the oblique-divergent plate boundary within the Gulf of California. Detailed geologic and geomorphic mapping along the onshore San Juan de los Planes and Saltito fault zones allowed us to delineate geometric sections and to infer the tectonic history of the fault zones. To achieve a more complete understanding of these individual normal faults within a larger array, we mapped faults to ~10 km offshore using seismic CHIRP (compressed high-intensity radar pulse) profiling. Both onshore faults slip at a low rate and have a low total offset. Along the San Juan de los Planes fault zone, which is entirely onshore, the young, scarp-forming fault reactivated older faults to rupture a broad, low-relief pediment surface with thin Quaternary cover, reflecting a two-stage slip history along this fault zone. The offshore study suggests a northward continuation of the onshore Saltito fault, and a complex fault array north of the La Gata fault on the east side of the San Juan de los Planes basin extending northward to the west Cerralvo fault. Our results suggest relatively low rates of active faulting of 〈1 mm/yr across the San Juan de los Planes system of faults compared to high rates on the active gulf-axis system, and relatively higher rates on earlier Neogene gulf margin faults in other areas along the southwest Gulf of California margin.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 10
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    Late Quaternary faulting history of the Carrizal and related faults, La Paz region, Baja California Sur, Mexico (2014)
    Geological Society of America (GSA)
    In: Geosphere
    Details
    Publication Date: 2014-05-29
    Description: The southwest margin of the Gulf of California has an array of active normal faults despite this being an oblique-divergent plate boundary with spreading centers that localized deformation along the plate boundary 2–3 million years ago. The Carrizal and Centenario faults form the western border fault of the Gulf of California marginal fault system within and south of La Paz Bay, and ~20–30 km west of the capital city of La Paz, Baja California Sur, Mexico. Geologic and geomorphic mapping, optically stimulated luminescence (OSL) geochronology, and paleoseismic investigations onshore, compressed high-intensity radar pulse (CHIRP) profiling offshore, and analysis of uplifted marine terraces in the footwall of the offshore Carrizal fault provide some of the first numerical and geometrical constraints on late Pleistocene–Holocene faulting along the Carrizal fault. The onshore Carrizal fault has ruptured with up to ~1–2 m of vertical displacement per event, likely producing ~M 6.3–6.9 earthquakes, and at least two to three surface rupturing earthquakes have occurred since 22 ka. Onshore paleoseismic excavations and uplifted marine terraces on the western side of La Paz Bay both suggest offset rates of 0.1–0.2 mm/yr, with a footwall uplift rate of 0.13 mm/yr since 128 ka, and an approximately constant rate since marine oxygen-isotope stage (MIS) 11 terraces (420 ka). A CHIRP survey identified underwater fault scarps with heights ranging from 21 to 86 m on the Carrizal fault in La Paz Bay and from 3 to 5 m along the Centenario fault. The offshore Carrizal fault lies 8–10 km east of the western edge of La Paz Bay, forming a right step from the onshore Carrizal fault. The offshore Carrizal fault is the oldest fault of the fault system, and the fault likely grew in the latest Miocene to Pliocene in a complex way to the south toward the onshore Centenario and Carrizal faults. When the Alarcon spreading center started its modern rates at 2.4 Ma, the Carrizal fault likely slowed to the 0.1–0.2 mm/yr rates of the late Quaternary determined in this study.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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