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  • 1
    Online-Ressource
    Online-Ressource
    Kinematics of Fault Slip Associated with the 4–6 July 2019 Ridgecrest, California, Earthquake Sequence
    Seismological Society of America (SSA) ; 2020
    In:  Bulletin of the Seismological Society of America Vol. 110, No. 4 ( 2020-08-01), p. 1688-1700
    Details
    In: Bulletin of the Seismological Society of America, Seismological Society of America (SSA), Vol. 110, No. 4 ( 2020-08-01), p. 1688-1700
    Kurzfassung: The 2019 Ridgecrest, California, earthquake sequence produced observable crustal deformation over much of central and southern California, as well as surface rupture over several tens of kilometers. To obtain a detailed picture of the fault slip involved in the 4 July M 6.4 foreshock and 6 July M 7.1 mainshock, we combine strong-motion seismic waveforms with crustal deformation observations to obtain kinematic and static slip models of both events. We sample the regional seismic wavefield for both the foreshock and mainshock with three-component records from 31 stations of the California Integrated Seismic Network. The deformation observations include Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), and borehole strainmeter recordings of the dynamic strain field. These data collectively constrain the kinematic coseismic slip distributions of the events, with measurements variously observing coseismic slip from one event (e.g., seismic waveforms, kinematic solutions from continuous GPS, and strainmeter time series) or coseismic slip from both events combined (InSAR). We find that the foreshock ruptured two separate faults, one with left-lateral strike slip on a northeast–southwest-trending fault and the other with right-lateral strike slip on an orthogonal fault, with unilateral rupture propagation along both. The mainshock ruptured a series of northwest–southeast-trending faults with right-lateral strike slip concentrated in the uppermost 6 km with exceptionally low-rupture velocity averaging 1.0–1.5  km/s. A possible explanation for the low-rupture velocity is that the mainshock rupture expended relatively high energy, generating secondary fractures in off-fault deformation, which is consistent with field and seismic evidence of plastic deformation on small fault strands adjacent to the main rupture trace.
    Materialart: Online-Ressource
    ISSN: 0037-1106 , 1943-3573
    URL: Article
    DOI: 10.1785/0120200018
    Sprache: Englisch
    Verlag: Seismological Society of America (SSA)
    Publikationsdatum: 2020
    ZDB Id: 2065447-9
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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    Online-Ressource
  • 2
    Online-Ressource
    Online-Ressource
    Coseismic Slip and Early Afterslip of the M6.0 24 August 2014 South Napa, California, Earthquake
    American Geophysical Union (AGU) ; 2019
    In:  Journal of Geophysical Research: Solid Earth Vol. 124, No. 11 ( 2019-11), p. 11728-11747
    Details
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 124, No. 11 ( 2019-11), p. 11728-11747
    Kurzfassung: Fault slip of the South Napa earthquake is constrained by seismic waveforms, geodetic data, and surface observations of slip Models designed to fit the seismic and geodetic data favor a steeply east dipping fault geometry The earthquake was followed by afterslip amounting to about one third of the seismic moment of the mainshock
    Materialart: Online-Ressource
    ISSN: 2169-9313 , 2169-9356
    URL: Article
    DOI: 10.1029/2019JB018470
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2019
    ZDB Id: 2016813-5
    ZDB Id: 161666-3
    ZDB Id: 3094197-0
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Online-Ressource
    Online-Ressource
    Rapid Geodetic Observations of Spatiotemporally Varying Postseismic Deformation Following the Ridgecrest Earthquake Sequence: The U.S. Geological Survey Response
    Seismological Society of America (SSA) ; 2020
    In:  Seismological Research Letters Vol. 91, No. 4 ( 2020-07-01), p. 2108-2123
    Details
    In: Seismological Research Letters, Seismological Society of America (SSA), Vol. 91, No. 4 ( 2020-07-01), p. 2108-2123
    Kurzfassung: The U.S. Geological Survey’s geodetic response to the 4–5 July 2019 (Pacific time) Ridgecrest earthquake sequence comprised primarily the installation and/or reoccupation of Global Navigation Satellite System (GNSS) monumentation. Our response focused primarily on the United States’ Navy’s China Lake Naval Air Weapons Station base (NAWSCL). This focus was because much of the surface rupture occurred on the NAWSCL and because of NAWSCL access restrictions only permitting Federal and State of California personnel. In total, we measured or are still measuring at 24 sites, 14 of which were on the NAWSCL and, as of this writing, operational. The majority of sites were set up as continuous stations logging at either 1 sample per second or 1 sample per 15 s. Two stations were recording a 200 m cross-rupture aperture starting ∼10  hr after the M 6.4 event, and they recorded the coseismic displacements of the M 7.1. Approximately, 1 hr after the M 7.1 event, two new stations were recording a ∼200  m cross-rupture aperture of the surface rupture. In the days following, we established the rest of the stations ranging to a distance of ∼15  km from the M 7.1 principal rupture trace. The lack of differential displacement across the M 6.4 rupture during the M 7.1 event suggests that it did not reactivate the M 6.4 plane. The lack of differential cross-fault displacement for both events suggests that rapid shallow afterslip did not occur at those two locations. The postseismic time series from these stations shows centimeters of horizontal displacement over periods of a few months. They record a mixture of fault-parallel and fault-normal displacements that, in conjunction with analysis of more spatially complete Interferometric Synthetic Aperture Radar displacement fields, suggest that both poroelastic and afterslip phenomena occur along the M 6.4 and 7.1 rupture planes. Using preliminary data from these and other regional stations, we also explore the Ridgecrest sequence’s effect on regional GNSS time series and the differentiation of long-term postseismic motions and secular deformation rates. We find that redefining a common-mode noise filter using different GNSS stations that are assumed to be unaffected by the earthquakes results in small but systematic differences in the regional velocity field estimate.
    Materialart: Online-Ressource
    ISSN: 0895-0695 , 1938-2057
    URL: Article
    DOI: 10.1785/0220200007
    Sprache: Englisch
    Verlag: Seismological Society of America (SSA)
    Publikationsdatum: 2020
    ZDB Id: 2403376-5
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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    Online-Ressource
  • 4
    Online-Ressource
    Online-Ressource
    Postseismic Relaxation Following the 2019 Ridgecrest, California, Earthquake Sequence
    Seismological Society of America (SSA) ; 2022
    In:  Bulletin of the Seismological Society of America Vol. 112, No. 2 ( 2022-04-01), p. 734-749
    Details
    In: Bulletin of the Seismological Society of America, Seismological Society of America (SSA), Vol. 112, No. 2 ( 2022-04-01), p. 734-749
    Kurzfassung: The 2019 Ridgecrest, California, earthquake sequence involved predominantly right-lateral strike slip on a northwest–southeast-trending subvertical fault in the 6 July M 7.1 mainshock, preceded by left-lateral strike slip on a northeast–southwest-trending subvertical fault in the 4 July M 6.4 foreshock. To characterize the postseismic deformation, we assemble displacements measured by Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar. The geodetic measurements illuminate vigorous postseismic deformation for at least 21 months following the earthquake sequence. The postseismic transient deformation is particularly well constrained from survey-mode GPS (sGPS) in the epicentral region carried out during the weeks after the mainshock. We interpret these observations with mechanical models including afterslip and viscoelastic relaxation of the lower crust and mantle asthenosphere. During the first 21 months, up to several centimeters of horizontal motions are measured at continuous GPS and sGPS sites, with amplitude that diminishes slowly with distance from the mainshock rupture, suggestive of deeper afterslip or viscoelastic relaxation. We find that although afterslip involving right-lateral strike slip along the mainshock fault traces and their deeper extensions reach a few decimeters, most postseismic deformation is attributable to viscoelastic relaxation of the lower crust and mantle. Within the Basin and Range crust and mantle, we infer a transient lower crust viscosity several times that of the mantle asthenosphere. The transient mantle asthenosphere viscosity is ∼1.3×1017  Pa s, and the adjacent Central Valley transient mantle asthenosphere viscosity is ∼7×1017  Pa s, about five times higher and consistent with an asymmetry in postseismic horizontal motions across the mainshock surface rupture.
    Materialart: Online-Ressource
    ISSN: 0037-1106 , 1943-3573
    URL: Article
    DOI: 10.1785/0120210170
    Sprache: Englisch
    Verlag: Seismological Society of America (SSA)
    Publikationsdatum: 2022
    ZDB Id: 2065447-9
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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    Online-Ressource
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