Research Article

Hierarchical interlocked orthogonal faulting in the 2019 Ridgecrest earthquake sequence

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Science  18 Oct 2019:
Vol. 366, Issue 6463, pp. 346-351
DOI: 10.1126/science.aaz0109
  • Fig. 1 Overview of study area.

    Mapped faults are indicated in brown. Ridgecrest sequence epicenters are shown as blue dots for time period up to the Mw 7.1 mainshock and as red dots following the mainshock. Santa Barbara, Los Angeles, Ventura, Palm Springs, and Ridgecrest and the LLFZ are denoted SB, LA, V, PS, RC, and LLFZ, respectively. Inset shows magnitude-time evolution of the first three days of the sequence. Note the catalog incompleteness during the first few days after the largest events. The Mw 6.4 event was preceded by a prominent foreshock sequence.

  • Fig. 2 Map view of Ridgecrest seismicity.

    Black lines indicate the surface trace of the fault (31), and purple lines indicate quaternary faults. Events with Mw of >4.5 are indicated by focal mechanisms (32). The fault network exhibits multiscale orthogonal faulting throughout the region, with a bifurcation to the southeast and horsetail faulting at the northwest terminus. The lower panel shows a seismicity cross section for events within 1 km of A-A′ with interpreted faults drawn shown as brown lines. At least 20 orthogonal faults cut through this profile. The dashed red line indicates the surface trace of southwest-trending fault that ruptured in the Mw 6.4 event.

  • Fig. 3 Interferogram and DPM.

    (A) Coseismic interferogram derived from the ALOS-2 SAR image pair (2018-04-16 and 2019-07-08), showing the locations of surface ruptures. The line of site (LOS) is from ground to satellite. (B) DPM derived from coherence loss between pre- and postseismic Sentinel-1 SAR data. Darker colors indicate greater coherence losses.

  • Fig. 4 Kinematic summary of rupture processes.

    The Mw 6.4 foreshock ruptured three main faults. This event was followed by foreshock activity along a northwest-trending fault and eventually triggered the Mw 7.1 event. The mainshock had four main subevents and ruptured bilaterally. Both events have very slow rupture velocities of ~2 km/s.

  • Fig. 5 Static inversion of geodetic data.

    (A) Mean slip model of the Ridgecrest sequence, including the slip contribution from the Mw 6.4 and Mw 7.1 events. (B) Black lines show the fault geometries used in the slip. Arrows indicate the data (black) and model prediction (red) of nearby GPS offsets. The color map indicates the displacements in the unwrapped ALOS2 ascending track 65 coseismic interferogram along the corresponding line-of-sight (LOS) direction (black arrow). Model predictions and data residuals are provided in the supplementary materials (11).

  • Fig. 6 Summary of triggered creep on the Garlock fault.

    Step function fit at the coseismic time for Sentinel 1, ascending track 64 InSAR time series, combined with gradient shading of the same field. The gradient shading reveals zones of surface offset along the Garlock fault. Fault perpendicular profiles reveal offset of up to 20 mm in the line-of-sight direction, while the width of the deformation profiles suggest that offset on the fault is confined to shallow depths.

Supplementary Materials

  • Hierarchical interlocked orthogonal faulting in the 2019 Ridgecrest earthquake sequence

    Zachary E. Ross, Benjamín Idini, Zhe Jia, Oliver L. Stephenson, Minyan Zhong, Xin Wang, Zhongwen Zhan, Mark Simons, Eric J. Fielding, Sang-Ho Yun, Egill Hauksson, Angelyn W. Moore, Zhen Liu, Jungkyo Jung

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods 
    • Figs. S1 to S19
    • Tables S1 to S4 
    • References 

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