Abundant off-fault seismicity and orthogonal structures in the San Jacinto fault zone

Ross, Zachary E.; Hauksson, Egill; Ben‐Zion, Yehuda

doi:10.1126/sciadv.1601946

Cited by 104 publications

(109 citation statements)

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“…The scaling parameter ε 1 =0.35 (± 0.064) inferred using the weighted regression procedure described in section 3.1 is the highest of any of the five regions in our study and would be on the higher end of previously reported values, which typically are in the range of 0.1–0.4 [ Mayeda and Walter , ; Izutani and Kanamori , ; Kanamori and Rivera , ; Takahashi et al , ; Mayeda et al , ; Venkataraman et al , ; Pacor et al , ]. This trend in scaling is persistent over the duration of our study period (Figure b, right) and may in part be related to fact that the larger ( M ≥3.5) events in the trifurcation zone tend to occur along the three major fault strands, while microseismicity preferentially occurs in the off‐fault and intrafault regions [ Ross et al , ]. A full exploration into the causative mechanisms of this strong regional trend in scaling is, however, beyond the scope of this study.…”

Section: Resultsmentioning

confidence: 99%

Application of an improved spectral decomposition method to examine earthquake source scaling in Southern California

2017

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Earthquake source spectra contain fundamental information about the dynamics of earthquake rupture. However, the inherent tradeoffs in separating source and path effects, when combined with limitations in recorded signal bandwidth, make it challenging to obtain reliable source spectral estimates for large earthquake data sets. We present here a stable and statistically robust spectral decomposition method that iteratively partitions the observed waveform spectra into source, receiver, and path terms. Unlike previous methods of its kind, our new approach provides formal uncertainty estimates and does not assume self‐similar scaling in earthquake source properties. Its computational efficiency allows us to examine large data sets (tens of thousands of earthquakes) that would be impractical to analyze using standard empirical Green's function‐based approaches. We apply the spectral decomposition technique to P wave spectra from five areas of active contemporary seismicity in Southern California: the Yuha Desert, the San Jacinto Fault, and the Big Bear, Landers, and Hector Mine regions of the Mojave Desert. We show that the source spectra are generally consistent with an increase in median Brune‐type stress drop with seismic moment but that this observed deviation from self‐similar scaling is both model dependent and varies in strength from region to region. We also present evidence for significant variations in median stress drop and stress drop variability on regional and local length scales. These results both contribute to our current understanding of earthquake source physics and have practical implications for the next generation of ground motion prediction assessments.

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Section: Resultsmentioning

confidence: 99%

Application of an improved spectral decomposition method to examine earthquake source scaling in Southern California

2017

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“…In the spatial domain, such patterns exist from large‐scale faulting (i.e., the long timescale as well) down to laboratory samples (Fossen, ). On intermediate time scales, they are also clearly observable on structures delineated by earthquake catalogs, such as in the San Jacinto area (Ross et al, ), for instance. At the scale of aftershock sequences, one of the most famous examples is one of the Elmore Ranch ( M = 6.2) and Superstition Hills (M = 6.6) earthquake sequence (Hudnut et al, ), with two conjugate events of similar magnitudes occurring on 24 November 1987.…”

Section: Discussionmentioning

confidence: 99%

Magnitude of Earthquakes Controls the Size Distribution of Their Triggered Events

Nandan¹,

Ouillon²,

Sornette

2019

JGR Solid Earth

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The driving concept behind one of the most successful statistical forecasting models, the Epidemic Type Aftershock Sequence (ETAS) model, has been that the seismicity is driven by spontaneously occurring background earthquakes that cascade into multitudes of triggered earthquakes. In nearly all generalizations of the ETAS model, the magnitudes of the background and the triggered earthquakes are assumed to follow Gutenberg‐Richter law with the same exponent (β value). Furthermore, the magnitudes of the triggered earthquakes are always assumed to be independent of the magnitude of the triggering earthquake. Using an expectation maximization algorithm applied to the Californian earthquake catalog, we show that the distribution of earthquake magnitudes exhibits three distinct β values: βb for background events and βa − δ and βa + δ, respectively, for triggered events below and above the magnitude of the triggering earthquake; the two last values express a correlation between the magnitudes of triggered events with that of the triggering earthquake, a feature so far absent in all proposed operational generalizations of the ETAS model. The ETAS model incorporating this kinked magnitude distribution provides by far the best description of seismic catalogs and could thus have the best forecasting potential. We speculate that the kinked magnitude distribution may result from the system tending to restore the symmetry of the regional displacement gradient tensor that has been broken by the initiating event. The general emerging concept could be that while the background events occur primarily to accommodate the symmetric stress tensor at the boundaries of the system, the triggered earthquakes are quasi‐Goldstone fluctuations of a self‐organized critical deformation state.

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“…With our presented 2‐D plane strain model we neglect the third dimension and instead assume perfectly vertical fault surfaces. This is valid in a first‐order sense; however, various natural strike‐slip faults can have changing dip angles with depth (e.g., Ross et al, ). Another drawback of our 2‐D simulations is the finiteness of the seismogenic depth.…”

Section: Discussionmentioning

confidence: 99%

Seismic and Aseismic Fault Growth Lead to Different Fault Orientations

et al. 2019

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Orientations of natural fault systems are subject to large variations. They often contradict classical Coulomb failure theory as they are misoriented relative to the regional Andersonian stress field. This is ascribed to local effects of structural or stress heterogeneities and reorientations of structures or stresses on the long term. To better understand the relation between fault orientation and regional stresses, we simulate spontaneous fault growth and its effect on the stress field. Our approach incorporates earthquake rupture dynamics, viscoelastoplastic brittle deformation and a rate‐ and state‐dependent friction formulation in a continuum mechanics framework. We investigate how strike‐slip faults orient according to local and far‐field stresses during their growth. We identify two modes of fault growth, seismic and aseismic, distinguished by different fault angles and slip velocities. Seismic fault growth causes a significant elevation of dynamic stresses and friction values ahead of the propagating fault tip. These elevated quantities result in a greater strike angle relative to the maximum principal regional stress than that of a fault segment formed aseismically. When compared to the near‐tip time‐dependent stress field the fault orientations produced by both growth modes follow the classical failure theory. We demonstrate how the two types of fault growth may be distinguished in natural faults by comparing their angles relative to the original regional maximum principal stress. A stress field analysis of the Landers‐Kickapoo fault suggests that an angle greater than ∼25° between two faults indicates seismic fault growth.

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Abundant off-fault seismicity and orthogonal structures in the San Jacinto fault zone

Abstract: Distinct on-fault and off-fault seismicity in the trifurcation area of the San Jacinto fault zone.

Cited by 104 publications

References 50 publications

Application of an improved spectral decomposition method to examine earthquake source scaling in Southern California

Application of an improved spectral decomposition method to examine earthquake source scaling in Southern California

Magnitude of Earthquakes Controls the Size Distribution of Their Triggered Events

Seismic and Aseismic Fault Growth Lead to Different Fault Orientations

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