Application of high-rate GPS for earthquake rapid response and modelling: a case in the 2019 Mw 7.1 Ridgecrest earthquake

Abstract

<jats:title>SUMMARY</jats:title> <jats:p>The 2019 Mw 7.1 Ridgecrest earthquake opens an opportunity to investigate how soon we can produce a reliable fault geometry and subsequently a robust source model based on high-rate Global Positioning System (GPS) data. In this study, we conduct peak ground displacement (PGD) magnitude scaling, real-time centroid moment tensor (CMT) calculation and rapid kinematic slip inversion. We conclude that a four-station PGD warning with a magnitude of Mw 7.03 can be issued at 24 s after initiation of the rupture. Fast CMT inversion can initially recover the correct nodal planes at 30 s. The kinematic slip model reveals that the Mw 7.1 earthquake is a predominant dextral strike-slip event with both normal and thrust components resolved. The earthquake shows a bilateral rupture with a low propagation speed of ∼2.1 km s−1 and a slip maxima of ∼4 m. The total moment is 5.18 × 1019 N m (Mw 7.11). We further suggest that a reasonable source model will be available in a simulated real-time mode within 30 s after the earthquake occurring, without using full high-rate GPS waveforms. This research highlights the significance of high-rate GPS for rapid earthquake response and modelling of kinematic rupture, which is also generalized by the hypothetical real-time GPS analysis for the 2016 Mw 7.8 Kaikoura earthquake and the 2010 Mw 7.2 El Mayor-Cucapah earthquake.</jats:p>

Structural Controls Over the 2019 Ridgecrest Earthquake Sequence Investigated by High‐Fidelity Elastic Models of 3D Velocity Structures

“…The general location of the Ridgecrest earthquakes' aftershocks can partially be explained by positively stressed zones, as revealed in the earlier studies (Fang et al., 2020; Hardebeck, 2020; Jin & Fialko, 2020; Li et al., 2020; Toda & Stein, 2020; K. Wang et al., 2020). Given the commonly accepted stress triggering threshold of 10 kPa (King et al., 1994), our results suggest that only 30%–40% of the relocated aftershocks experienced adequate coseismic ΔCFS (Figures 8e and 8f) and a larger proportion of aftershocks fall within the stress shadow zones (Fang et al., 2020; Jin & Fialko, 2020; Li et al., 2020; Toda & Stein, 2020; Wang et al., 2020), considering both the NW‐ and SW‐trending focal‐plane orientations (i.e., (strike, dip, rake) = (322, 81, −173) and (228,66,4) (USGS, 2020)). This observation could be due to the incomplete understandings of aftershock geometry, pre‐seismic stress states, dynamic stress perturbation, fault frictional properties, other triggering mechanisms (e.g., afterslip and poroelastic rebound), etc.…”

“…Concerning the velocity anomalies documented in the SCEC Community Velocity Model, the major asperities over the NWF (at 3–8 km depth) appear to sit over rock matrices of reduced stiffness (lower Δ E and higher Δ v ) (Figures 10c–10f). Given that the hypocenter of M w 7.1 and M w 6.4 earthquakes are also near a local Vs minimum along the NWF and SWF, respectively (Figure 2d), the observed M w 7.1 event's bilateral rupture and M w 6.4 event's unilateral rupture also support a tendency of slip propagating into the high‐velocity zones in the vicinity (Chen et al., 2020; Fang et al., 2020; Liu et al., 2019; Pollitz et al., 2020; K. Wang et al., 2020). Around 5 km below the M w 7.1 hypocenter and the major slip, significant afterslip (up to 1.5 m) are inferred by the prior studies (Feng et al., 2020; Pollitz et al., 2020) and coincidentally fell within a cone‐like structure of reduced V s at a depth of ∼10 km (Figure 2d).…”

“…Based on the overall displacement signatures, we generalize the coseismic rupture to contain two curvilinear faults (length > 25 km), namely, the SWF and NWF that primarily host the rupture of the Ridgecrest earthquake sequence (Figure 2). This setting may not include some of the minor segments but multiple studies showed that it adequately explains the fault kinematic rupture and recover the geodetic observations (Barnhart et al, 2019;Chen et al, 2020;Fang et al, 2020;Hirakawa & Barbour, 2020;Liu et al, 2019;Zhang et al, 2020).…”

“…This TUNG ET AL. setting may not include some of the minor segments but multiple studies showed that it adequately explains the fault kinematic rupture and recover the geodetic observations (Barnhart et al, 2019;Chen et al, 2020;Fang et al, 2020;Hirakawa & Barbour, 2020;Liu et al, 2019;Zhang et al, 2020).…”

“…Such kinked curvature of fault is outlined by irregular triangular meshes in our FEMs (Figure 2). We further test three different along‐strike configurations of the NWF approximated by the curvilinear trace, three fault planes (Chen et al., 2020; Jin & Fialko, 2020; Pollitz et al., 2020), and a single fault plane (Fang et al., 2020). The details of the FEM mesh and domain configurations are summarized in the supporting information and Table S2.…”