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  • Brooks, Benjamin A.  (2)
  • Roeloffs, Evelyn  (2)
  • 1
    Online Resource
    Online Resource
    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
    Abstract: 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.
    Type of Medium: Online Resource
    ISSN: 0037-1106 , 1943-3573
    URL: Article
    DOI: 10.1785/0120200018
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2020
    detail.hit.zdb_id: 2065447-9
    SSG: 16,13
    Location Call Number Limitation Availability
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    Online Resource
  • 2
    Online Resource
    Online Resource
    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
    Abstract: 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.
    Type of Medium: Online Resource
    ISSN: 0895-0695 , 1938-2057
    URL: Article
    DOI: 10.1785/0220200007
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2020
    detail.hit.zdb_id: 2403376-5
    SSG: 16,13
    Location Call Number Limitation Availability
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    Online Resource
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