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  • 1
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    The rise, collapse, and compaction of Mt. Mantap from the 3 September 2017 North Korean nuclear test (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-07-13
    Description: Surveillance of clandestine nuclear tests relies on a global seismic network, but the potential of spaceborne monitoring has been underexploited. We used satellite radar imagery to determine the complete surface displacement field of up to 3.5 meters of divergent horizontal motion with 0.5 meters of subsidence associated with North Korea’s largest underground nuclear test. Combining insight from geodetic and seismological remote sensing, we found that the aftermath of the initial explosive deformation involved subsidence associated with subsurface collapse and aseismic compaction of the damaged rocks of the test site. The explosive yield from the nuclear detonation with best-fitting source parameters for 450-meter depth was 191 kilotonnes of TNT equivalent. Our results demonstrate the capability of spaceborne remote sensing to help characterize large underground nuclear tests.
    Keywords: Geochemistry, Geophysics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    The 2014 Mw 6.1 South Napa Earthquake: A Unilateral Rupture with Shallow Asperity and Rapid Afterslip (2015)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2015-03-05
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 3
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    Under the hood of the earthquake machine: toward predictive modeling of the seismic cycle (2012)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2012-05-15
    Description: Advances in observational, laboratory, and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power. To explore that possibility, we developed an integrative and fully dynamic model of the Parkfield segment of the San Andreas Fault. The model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude (M(w)) 6.0 main shocks--including events similar to the ones in 1966 and 2004--and provides an excellent match for the detailed interseismic, coseismic, and postseismic observations collected along this fault during the most recent earthquake cycle. Such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Barbot, Sylvain -- Lapusta, Nadia -- Avouac, Jean-Philippe -- New York, N.Y. -- Science. 2012 May 11;336(6082):707-10. doi: 10.1126/science.1218796.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA. sbarbot@caltech.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22582259" 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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    Change of Apparent Segmentation of the San Andreas Fault Around Parkfield from Space Geodetic Observations Across Multiple Periods (2013)
    Wiley
    Details
    Publication Date: 2013-11-17
    Description: [1]  Sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by co- and postseismic phases of stress release. Because the recurrence time of large earthquakes is often greater than the available span of space geodetic data, it has been challenging to monitor the evolution of interseismic loading in its entire duration. Here, we analyze large datasets of surface deformation at different key episodes around the Cholame, Parkfield, and creeping segments of the San Andreas Fault that show evidence of significant deceleration of fault slip during the interseismic period. We compare the average fault slip rates before and after the 2004 Mw 6 Parkfield earthquake, in the 1986-2004 and 2006-2012 periods, respectively, avoiding two years of postseismic deformation after 2004. Using a combination of GPS data from the Plate Boundary Observatory, the SCEC Crustal Motion Map and the Bay Area Velocity Unification networks and interferometric synthetic aperture radar from the ALOS and ENVISAT satellites, we show that the area of coupling at the transition between the Parkfield and Cholame segments appears larger later in the interseismic period than it does earlier on. While strong platecoupling is uniform across the Parkfield and Cholame segments in the 1986-2004 period, creep occurs south of the 2004 epicenter after 2006, making segmentation of the San Andreas Fault south of Parkfield more clearly apparent. These observations indicate that analyses of surface deformation late in the earthquake cycle may over-estimate the area of plate coupling. A fault surface creeping much below plate rate may in some case be a region that does not promote earthquake nucleation, but rather just be at a slower stage of its evolution. Our analysis also shows signs of large variation of slip velocity above and below plate rate in the creeping segment indicating that cycles of weakening and hardening can also be at play in dominantly aseismic areas.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Constraining the Kinematics of Metropolitan Los Angeles Faults with a Slip-Partitioning Model (2016)
    Wiley
    Details
    Publication Date: 2016-10-29
    Description: Due to the limited resolution at depth of geodetic and other geophysical data, the geometry and the loading rate of the ramp-décollement faults below the metropolitan Los Angeles are poorly understood. Here, we complement these data by assuming conservation of motion across the Big Bend of the San Andreas Fault. Using a Bayesian approach, we constrain the geometry of the ramp-décollement system from the Mojave block to Los Angeles and propose a partitioning of the convergence with 25.5 ± 0.5 mm/yr and 3.1 ± 0.6 mm/yr of strike-slip motion along the San Andreas Fault and the Whittier Fault, with 2.7 ± 0.9 mm/yr and 2.5 ± 1.0 mm/yr of updip movement along the Sierra Madre and the Puente Hills thrusts. Incorporating conservation of motion in geodetic models of strain accumulation reduces the number of free parameters and constitutes a useful methodology to estimate the tectonic loading and seismic potential of buried fault networks.
    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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  • 6
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    The Parkfield tremors reveal slow and fast ruptures on the same asperity (2016)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2016-04-05
    Description: The deep extension of the San Andreas Fault is believed to be creeping, but the recent observations of tectonic tremors from these depths indicate a complex deformation style. In particular, an isolated tremor source near Parkfield has been producing a sequence of low-frequency earthquakes that indicates an uncommon mechanism of stress accumulation and release. The tremor pattern regularly oscillated between three and six days from mid-2003 until it was disrupted by the 2004 magnitude 6.0 Parkfield earthquake. After that event, the tremor source ruptured only about every three days, but over the next two years it gradually returned to its initial alternating recurrence pattern. The mechanism that drives this recurrence pattern is unknown. Here we use physics-based models to show that the same tremor asperity--the region from which the low-frequency earthquakes radiate--can regularly slip in slow and fast ruptures, naturally resulting in recurrence intervals alternating between three and six days. This unusual slip behaviour occurs when the tremor asperity size is close to the critical nucleation size of earthquakes. We also show that changes in pore pressure following the Parkfield earthquake can explain the sudden change and gradual recovery of the recurrence intervals. Our findings suggest a framework for fault deformation in which the same asperity can release tectonic stress through both slow and fast ruptures.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Veedu, Deepa Mele -- Barbot, Sylvain -- England -- Nature. 2016 Apr 21;532(7599):361-5. doi: 10.1038/nature17190. Epub 2016 Apr 4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Earth Observatory of Singapore, Asian School of the Environment, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27042936" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 7
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    Along-strike variations of the partitioning of convergence across the Haiyuan fault system detected by InSAR (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-03
    Description: Oblique convergence across Tibet leads to slip partitioning with the coexistence of strike-slip, normal and thrust motion on major fault systems. A key point is to understand and model how faults interact and accumulate strain at depth. Here, we extract ground deformation across the Haiyuan Fault restraining bend, at the northeastern boundary of the Tibetan plateau, from Envisat radar data spanning the 2001–2011 period. We show that the complexity of the surface displacement field can be explained by the partitioning of a uniform deep-seated convergence. Mountains and sand dunes in the study area make the radar data processing challenging and require the latest developments in processing procedures for Synthetic Aperture Radar interferometry. The processing strategy is based on a small baseline approach. Before unwrapping, we correct for atmospheric phase delays from global atmospheric models and digital elevation model errors. A series of filtering steps is applied to improve the signal-to-noise ratio across high ranges of the Tibetan plateau and the phase unwrapping capability across the fault, required for reliable estimate of fault movement. We then jointly invert our InSAR time-series together with published GPS displacements to test a proposed long-term slip-partitioning model between the Haiyuan and Gulang left-lateral Faults and the Qilian Shan thrusts. We explore the geometry of the fault system at depth and associated slip rates using a Bayesian approach and test the consistency of present-day geodetic surface displacements with a long-term tectonic model. We determine a uniform convergence rate of 10 [8.6–11.5] mm yr –1 with an N89 [81–97]°E across the whole fault system, with a variable partitioning west and east of a major extensional fault-jog (the Tianzhu pull-apart basin). Our 2-D model of two profiles perpendicular to the fault system gives a quantitative understanding of how crustal deformation is accommodated by the various branches of this thrust/strike-slip fault system and demonstrates how the geometry of the Haiyuan fault system controls the partitioning of the deep secular motion.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 8
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    Lower-crustal rheology and thermal gradient in the Taiwan orogenic belt illuminated by the 1999 Chi-Chi earthquake (2019)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2019
    Description: 〈p〉The strength of the lithosphere controls tectonic evolution and seismic cycles, but how rocks deform under stress in their natural settings is usually unclear. We constrain the rheological properties beneath the Taiwan orogenic belt using the stress perturbation following the 1999 Chi-Chi earthquake and fourteen-year postseismic geodetic observations. The evolution of stress and strain rate in the lower crust is best explained by a power-law Burgers rheology with rapid increases in effective viscosities from ~10〈sup〉17〈/sup〉 to ~10〈sup〉19〈/sup〉 Pa s within a year. The short-term modulation of the lower-crustal strength during the seismic cycle may alter the energy budget of mountain building. Incorporating the laboratory data and associated uncertainties, inferred thermal gradients suggest an eastward increase from 19.5±2.5°C/km in the Coastal Plain to 32±3°C/km in the Central Range. Geodetic observations may bridge the gap between laboratory and lithospheric scales to investigate crustal rheology and tectonic evolution.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    The mechanism of partial rupture of a locked megathrust: The role of fault morphology (2016)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2016-10-08
    Description: Assessment of seismic hazard relies on estimates of how large an area of a tectonic fault could potentially rupture in a single earthquake. Vital information for these forecasts includes which areas of a fault are locked and how the fault is segmented. Much research has focused on exploring downdip limits to fault rupture from chemical and thermal boundaries, and along-strike barriers from subducted structural features, yet we regularly see only partial rupture of fully locked fault patches that could have ruptured as a whole in a larger earthquake. Here we draw insight into this conundrum from the 25 April 2015 M w 7.8 Gorkha (Nepal) earthquake. We invert geodetic data with a structural model of the Main Himalayan thrust in the region of Kathmandu, Nepal, showing that this event was generated by rupture of a décollement bounded on all sides by more steeply dipping ramps. The morphological bounds explain why the event ruptured only a small piece of a large fully locked seismic gap. We then use dynamic earthquake cycle modeling on the same fault geometry to reveal that such events are predicted by the physics. Depending on the earthquake history and the details of rupture dynamics, however, great earthquakes that rupture the entire seismogenic zone are also possible. These insights from Nepal should be applicable to understanding bounds on earthquake size on megathrusts worldwide.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 10
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    Imaging the distribution of transient viscosity after the 2016 Mw 7.1 Kumamoto earthquake (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-15
    Description: The deformation of mantle and crustal rocks in response to stress plays a crucial role in the distribution of seismic and volcanic hazards, controlling tectonic processes ranging from continental drift to earthquake triggering. However, the spatial variation of these dynamic properties is poorly understood as they are difficult to measure. We exploited the large stress perturbation incurred by the 2016 earthquake sequence in Kumamoto, Japan, to directly image localized and distributed deformation. The earthquakes illuminated distinct regions of low effective viscosity in the lower crust, notably beneath the Mount Aso and Mount Kuju volcanoes, surrounded by larger-scale variations of viscosity across the back-arc. This study demonstrates a new potential for geodesy to directly probe rock rheology in situ across many spatial and temporal scales.
    Keywords: Geochemistry, Geophysics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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