The 2020 Monte Cristo (Nevada) Earthquake Sequence: Stress Transfer in the Context of Conjugate Strike‐Slip Faults

Abstract

On 15 May 2020 at 11:03 (UTC) a shallow earthquake with a Magnitude Mw 6.5 struck the Central Walker Lane in the Mina Deflection region. This shallow event offers the possibility to model the change in Coulomb failure function (ΔCFF) including the historical events and to analyze the effect of fluid redistribution on fault ruptures. The static stress change modeling shows that the 1932 Cedar Mountain (Mw 7.1) earthquake increased ΔCFF on the 2020 Monte Cristo left‐lateral rupture by an average value of ∼2 bar suggesting a fault interaction in the context of conjugate strike‐slip faults. Also, the ΔCFF caused by the Monte Cristo earthquake shows a 0.1–0.5 bar increase on nearby right‐lateral fault planes at 8 km depth. In contrast to the 2019 Ridgecrest sequence (Mw 6.4 and Mw 7.1), our poroelastic stress change modeling of the 2020 Monte Cristo earthquake shows no apparent correlation between the positive stress change values and fluid redistribution along the Monte Cristo conjugated ruptures. Nevertheless, the Coulomb modeling using adapted poroelastic solutions shows that the 2020 Monte Cristo mainshock increased stresses with a value of 0.2–0.9 bar south of the Mina Deflection along the White Mountains and Fish Lake Valley fault zones. The stress values combined with a strain rate of 40–50 nanostrain/yr represent a shift of 8%–15% of the recurrence time interval for a large earthquake along the White Mountains and Fish Lake Valley faults suggesting an elevated pore‐fluid effect for faults reactivation in both undrained and drained fluid conditions.

Role of fluid on earthquake occurrence: Example of the 2019 Ridgecrest and the 1997, 2009 and 2016 Central Apennines sequences

“…Based on these considerations, the temporal and spatial evolution in stress drop can not only be explained by the variation of the frictional property of rocks. Our results tend to validate the role of fluid in controlling both nucleation and the size of major fault ruptures in the SWL-ECSZ (Tong et al, 2021;Kariche, 2022). Note that the possible role of pore pressure variation on the complex distribution of stress drop during the 2019 Ridgecrest sequence was also examined by Trugman, (2020).…”

“…This recurrence pattern has been culminated by the occurrence of the 2019 Ridgecrest sequence (Mw 6.4; Mw 7.1). The study of the mechanics of earthquake and fault interaction in the context of conjugate strike-slip faults indicate a clear influence of fluid migration on the occurrence of moderate to large earthquakes in the SWL tectonic domain (Kariche, 2022). Based on the Coulomb poroelastic stress change modeling approach, the time delay between two conjugate strike-slip earthquakes seems to be coupled to the variation in fluid diffusivity along heterogeneous faults (Kariche, 2022).…”

“…The study of the mechanics of earthquake and fault interaction in the context of conjugate strike-slip faults indicate a clear influence of fluid migration on the occurrence of moderate to large earthquakes in the SWL tectonic domain (Kariche, 2022). Based on the Coulomb poroelastic stress change modeling approach, the time delay between two conjugate strike-slip earthquakes seems to be coupled to the variation in fluid diffusivity along heterogeneous faults (Kariche, 2022). These observations are in concordance with the Cocco & Rice (2002) Coulomb stress transfer modeling results taking into account the presence of high pore fluid pressure at hypocentral depth.…”

“…Considering the ~34 hr characteristic time delay of the 2019 Ridgecrest sequence representing the time delay between the Mw 6.4 foreshock and the Mw 7.1 mainshock (Kariche, 2022) and a fluid viscosity of 3x10 -4 Pa.s, the average value of permeability necessary to trigger the Mw7.1 Ridgecrest event is estimated between 10 -14 -10 -15 m 2 . Despite the fact that this value is higher than the value obtained by Cocco and Rice (2002) for normal fault geometries, it seems to be in a good agreement with the permeability values obtained recently by Miller…”

“…The high Vp/Vs ratio covering the complex fault zones of the 2019 Ridgecrest foreshock-mainshock sequence (Tong et al, 2021) denotes that the change in the pore-fluid pressure near the Ridgecrest fault zone may be considered as one of the plausible mechanisms explaining the diffuse inelastic deformation observed during the 2019 Ridgecrest sequence. A stress changes modeling results taking onto account the variation in the Vp/Vs ratio due to the diffusive effect of fluids during the Mw6.4 Ridgecrest foreshock reveals that the value of fluid diffusivity necessary to trigger the next Mw7.1 mainshock is estimated to ≤ 2.32 10 4 cm 2 /s (Kariche, 2022). This value seems to be low compared with the value obtained by Hudnut et al, (1989) for the 1987 Superstition Hills sequence and may explain the difference in the time delay between mainshocks in relation with to the two sequences.…”