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  • 1
    Publication Date: 2023-01-13
    Description: The interseismic motion of GPS stations in a tectonically active, diffuse, strike-slip shear zone provide constraints on the overall deformation budget that can be compared to the summation of geologically-estimated fault slip rates to understand regional strain accommodation. The Walker Lane GPS velocities in this dataset represent a subset of GPS stations included in the Nevada Geodetic Laboratory MIDAS velocity solution (Blewitt et al., 2016, 2018; accessible at http://geodesy.unr.edu/velocities/midas.NA12.txt, last accessed 11/19/2020) . This dataset includes velocities for all GPS stations located between 34° N – 43° N latitude and 114° W – 123° W longitude with time series longer than 2.5 years from the semi-continuous MAGNET network operated by the Nevada Geodetic Laboratory (Blewitt et al., 2009) and neighboring continuous GPS stations. The MIDAS velocities are calculated using daily position data collected through August 2019 presented in the NA12 reference frame (Blewitt et al., 2013) , and corrected for the postseismic effects of historic ruptures in and surrounding the Walker Lane. The MIDAS algorithm is a median trend estimator that mitigates both seasonality and step discontinuities in the times series (Blewitt et al., 2016). The resulting velocities are insensitive to the coseismic and postseismic effects of earthquakes that occurred after the midpoint of the time series (Blewitt et al., 2016) , such as the July 2019 Ridgecrest, CA M w 6.4 and 7.1 sequence, but must be corrected for the post-seismic effects of earthquakes that occurred prior to the middle of time series, such as the historic surface rupturing earthquakes in Central Nevada Seismic Belt and the 1993 Landers M w 7.3, and 1999 Hector Mine M w 7.0 events. We apply the viscoelastic postseismic relaxation correction from Bormann et al. (2013) that was developed using the method of Hammond et al. (2010) and the preferred western Basin and Range lower crust (10 20.5 Pa-s) and upper mantle (10 19 Pa-s) viscosity model of Hammond et al. (2009). When using this dataset, please also cite Blewitt et al (2018) as the authors of the original MIDAS NA12 reference frame velocity solution is the basis for our postseismic corrected Walker Lane velocities: Blewitt, G., Hammond, W.C., Kreemer, C., 2018. Harnessing the GPS Data Explosion for Interdisciplinary Science. Eos. https://doi.org/10.1029/2018EO104623.
    Keywords: Correlation; DATE/TIME; GDS; Geodesy station; LATITUDE; LONGITUDE; MIDAS_Nevada; NA12 reference frame; NA12 reference frame, postseismic corrected; Station label; Time in years; Velocity, east; Velocity, east, uncertainty; Velocity, north; Velocity, north, uncertainty; Year of observation
    Type: Dataset
    Format: text/tab-separated-values, 14157 data points
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  • 2
    Publication Date: 2021-07-21
    Description: Rockwall slope erosion is an important component of alpine landscape evolution, yet the role of climate and tectonics in driving this erosion remains unclear. We define the distribution and magnitude of periglacial rockwall slope erosion across 12 catchments in Himachal Pradesh and Jammu and Kashmir in the Himalaya of northern India using cosmogenic 10Be concentrations in sediment from medial moraines. Beryllium‐10 concentrations range from 0.5 ± 0.04 × 104 to 260.0 ± 12.5 × 104 at/g SiO2, which yield erosion rates between 7.6 ± 1.0 and 0.02 ± 0.004 mm/a. Between ∼0.02 and ∼8 m of rockwall slope erosion would be possible in this setting across a single millennium, and 〉2 km when extrapolated for the Quaternary period. This erosion affects catchment sediment flux and glacier dynamics, and helps to establish the pace of topographic change at the headwaters of catchments. We combine rockwall erosion records from the Himalaya of Himachal Pradesh, Jammu and Kashmir, and Uttarakhand in India and Baltistan in Pakistan to create a regional erosion data set. Rockwall slope erosion rates progressively decrease with distance north from the Main Central Thrust and into the interior of the orogen. The distribution and magnitude of this erosion is most closely associated with records of Himalayan denudation and rock uplift, where the highest rates of change are recorded in the Greater Himalaya sequences. This suggests that tectonically driven uplift, rather than climate, is a first order control on patterns of rockwall slope erosion in the northwestern Himalaya. Precipitation and temperature would therefore come as secondary controls.
    Description: Key Points: Rates of periglacial rockwall slope erosion are defined for the northwestern Himalaya using cosmogenic 10Be concentrations in sediment from medial moraines. Tectonically driven uplift offers a first‐order control on patterns of rockwall slope erosion. Precipitation and temperature play secondary roles in this erosion.
    Description: National Geographic Society http://dx.doi.org/10.13039/100006363
    Description: Geological Society of America http://dx.doi.org/10.13039/100005720
    Description: University of Cincinnati, Graduate Student Governance Association
    Description: PRIME Laboratories, Purdue University
    Keywords: 551.3 ; cosmogenic isotopes ; climate ; periglacial erosion ; rock uplift ; sediment flux
    Type: article
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  • 3
    Publication Date: 2021-09-27
    Description: Rockwall slope erosion is defined for the upper Bhagirathi catchment using cosmogenic Beryllium-10 (10Be) concentrations in sediment from medial moraines on Gangotri glacier. Beryllium-10 concentrations range from 1.1 ± 0.2 to 2.7 ± 0.3 × 104 at/g SiO2, yielding rockwall slope erosion rates from 2.4 ± 0.4 to 6.9 ± 1.9 mm/a. Slope erosion rates are likely to have varied over space and time and responded to shifts in climate, geomorphic and/or tectonic regime throughout the late Quaternary. Geomorphic and sedimentological analyses confirm that the moraines are predominately composed of rockfall and avalanche debris mobilized from steep relief rockwall slopes via periglacial weathering processes. The glacial rockwall slope erosion affects sediment flux and storage of snow and ice at the catchment head on diurnal to millennial timescales, and more broadly influences catchment configuration and relief, glacier dynamics and microclimates. The slope erosion rates exceed the averaged catchment-wide and exhumation rates of Bhagirathi and the Garhwal region on geomorphic timescales (103−105 years), supporting the view that erosion at the headwaters can outpace the wider catchment. The 10Be concentrations of medial moraine sediment for the upper Bhagirathi catchment and the catchments of Chhota Shigri in Lahul, northern India and Baltoro glacier in Central Karakoram, Pakistan show a tentative relationship between 10Be concentration and precipitation. As such there is more rapid glacial rockwall slope erosion in the monsoon-influenced Lesser and Greater Himalaya compared to the semi-arid interior of the orogen. Rockwall slope erosion in the three study areas, and more broadly across the northwest Himalaya is likely governed by individual catchment dynamics that vary across space and time. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons, Ltd.
    Keywords: 551.3 ; supraglacial processes ; sediment flux ; glacier ; climate ; cosmogenic isotopes
    Language: English
    Type: map
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  • 4
    Publication Date: 2009-06-22
    Description: The Manteigas-Braganca fault is a major, 250-km-long, NNE-striking, sinistral strike-slip structure in northern Portugal. This fault has no historical seismicity for large earthquakes, although it may have generated moderate (M5+) earthquakes in 1751 and 1858. Evidence of continued left horizontal displacement is shown by the presence of Cenozoic pull-apart basins as well as late Quaternary stream deflections. To investigate its recent slip history, a number of trenches were excavated at three sites along the Vilarica segment, north and south of the Douro River. At one site at Vale Meao winery, the occurrence of at least two and probably three events in the past 14.5 ka was determined, suggesting an average return period of about 5-7 ka. All three events appear to have occurred as a cluster in the interval between 14.5 and 11 ka, or shortly thereafter, suggesting a return period of less than 2 ka between events within the cluster. In the same area, a small offset rill suggests 2-2.5 m of slip in the most recent event and about 6.1 m after incision below a c. 16 ka alluvial fill event along the Douro River. At another site along the Vilarica River alluvial plain, NE of the Vale Meao site, several trenches were excavated in late Pleistocene and Holocene alluvium, and exposed the fault displacing channel deposits dated to between 18 and 23 ka. In a succession of closely spaced parallel cuts and trenches, the channel riser was traced into and across the fault to resolve c. 6.5 m of displacement after 18 ka and c. 9 m of slip after c. 23 ka. These observations yield a slip rate of 0.3-0.5 mm/a, which is consistent with earlier estimates. Combining the information on timing at Vale Meao winery and displacement at Vilarica argues for earthquakes in the M7+ range, with coseismic displacements of 2-3 m. This demonstrates that there are potential seismic sources in Portugal that are not associated with the 1755 Lisbon earthquake or the Tagus Valley, and, although rare, large events on the Vilarica fault could be quite destructive for the region. This work provides an analogue for the study of active faulting in intracontinental settings and supports the view that earthquakes within intracontinental settings tend to cluster in time. In addition, this study highlights the usefulness and application of multiple field, remote sensing and geochronological techniques for seismic hazard mitigation.
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  • 5
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    In:  Geological Society Special Publication 338: 389-407.
    Publication Date: 2010-09-28
    Description: The Himalayan-Tibetan orogen provides one of the best natural laboratories in which to examine the nature and dynamics of landscape development within continent-continent collision zones. Many new tectonic-climatic-geomorphological theories and models have emerged and/or have been greatly influenced as a consequence of the study of the region and the quest to understand its geomorphological development. These include models of the interactions between tectonics, climate and surfice processes, notably, the influence of climate on surface uplift by denudational unloading; the limiting of topography by glaciation (the glacial buzz-saw model); localized uplift at syntaxes by enhanced fluvial and glacial erosion that, in turn, weaken the lithosphere, enhancing surface uplift and exhumation (the tectonic aneurysm model); climate-driven out-of-sequence thrusting and crustal channel flow; glacial damming leading to differential erosion and uplift; paraglaciation; and the influence of extreme events such as earthquakes, landslides, and floods as major formative processes. The development of new technologies, including satellite remote sensing and global positioning systems, and analytical methods such as numerical dating is now allowing these theories and models to be tested and will inevitably lead to new paradigms.
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  • 6
  • 7
    Publication Date: 2020-12-01
    Print ISSN: 0169-555X
    Electronic ISSN: 1872-695X
    Topics: Geography , Geosciences
    Published by Elsevier
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  • 8
    Publication Date: 2012-04-01
    Description: The Camarillo fold belt in the Western Transverse Ranges poses a significant seismic hazard to nearly one million people living in Southern California, yet few published geologic or geochronological data from this fold belt exist. The Camarillo fold belt is composed of several south-verging, west-plunging anticlines that characterize the western extent of the Simi fault zone, which extends for 40 km through urbanized Ventura and Los Angeles Counties. Surface and subsurface geologic data are utilized to accurately construct five cross sections within discrete structural domains to assess the local style of deformation, and to quantify the magnitudes of fault slip, fault- and fold-related uplift, and percent shortening. Eight new optically stimulated luminescence (OSL) dates from three paleoseismic trenches and six numerical dates from a previous study were utilized to quantify the timing and rates of deformation on discrete faults and folds. The onset of deformation in the Camarillo fold belt is everywhere younger than ca. 125 ka and locally as young as ca. 25 ka. Quaternary deformation occurs on reactivated steeply dipping (70°) Miocene faults, with shortening being largely accommodated in a narrow zone (
    Print ISSN: 1941-8264
    Electronic ISSN: 1947-4253
    Topics: Geosciences
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  • 9
    Publication Date: 2012-04-01
    Description: The Las Posas and Ojai Valleys, located in the actively deforming Western Transverse Ranges of California, contain well-preserved flights of strath terraces and Quaternary strata (i.e., Saugus Formation) that when numerically dated elucidate the tectonic, geomorphic, and fluvial histories that sculpted the landscape since ca. 140 ka. This study includes 14 new optically stimulated luminescence and 16 new terrestrial cosmogenic nuclide ages from the late Pleistocene to Holocene that record two regional aggradation events and four intervals of strath terrace formation. Geochronologic data indicate that terrestrial Saugus strata in the Las Posas Valley (Camarillo Member) prograded over marine deposits at ca. 125 and 80 ka and are as young as 60–25 ka, which is an order of magnitude younger than the youngest Saugus strata elsewhere in Southern California. These results highlight the need for precise dating of Saugus strata where identified and utilized to assess rates of tectonic deformation. Based on its compositional character, thickness, stratigraphic relations, and inferred ages, the Camarillo member of the Saugus Formation is correlated with sediments of the Mugu aquifer identified in subcrop throughout the Ventura Basin and thus provides a new regional chronostratigraphic subsurface datum. The aggradation of these sediments and similar deposits in the study area between 13 and 4 ka is subsequent to the transition from humid to semiarid climate correlating to the end of the ultimate and penultimate glacial maximums. Aggradation is inferred to have resulted from increased sediment supply in response transient vegetative conditions and consequent hillslope destabilization. Similar to aggradational events, strath terrace cover sediments ages correlate to dry warm climate intervals, indicating straths in Southern California were cut at ca. 110–100 ka, 50–35 ka, 26–20 ka, and 15–4 ka. These results support recent mathematical and experimental models of strath formation, where increased sediment flux and decreased water discharge enhances lateral erosion rates and inhibits vertical incision. Subsequent incision and strath terrace formation is inferred to occur during intervening wet climate intervals. The correlation of strath terrace ages and aggradational events with environmental changes that are linked to global climate indicates that climate rather than tectonics exhibits first-order control of depositional, denudational, and incisional processes in the Western Transverse Ranges. Moreover, these results provide a chronostratigraphic framework that allows these landforms to be regionally correlated and used to assess rates of active tectonics where geochronologic data are unavailable.
    Print ISSN: 1941-8264
    Electronic ISSN: 1947-4253
    Topics: Geosciences
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  • 10
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