A Bimaterial Interface Along the Northern San Jacinto Fault Through Cajon Pass

Share, Pieter‐Ewald; Ben‐Zion, Yehuda

doi:10.1029/2018gl079834

Cited by 14 publications

(16 citation statements)

References 63 publications

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“…This agrees well with the observation of velocity contrast reversal across the SAF northwest and southeast of the SGP (Share & Ben‐Zion, ), The Vs around the ECSZ is much slower after the inversion, particularly for the region north to SGP for depths from 5 to 10 km (Figure ), which corresponds well with the area that has large damage volume in Ben‐Zion and Zaliapin (). The Salton Trough is imaged with a well‐defined shape of LVZ extended to depth 7 km in our final Vs model. Compared to the initial model, the velocities are much slower (~0.3 km/s) in the top 3–7 km. Different from the initial model, a clear shift in the velocity contrast interface location is observed by comparing Vs at 10 and 15 km for our final Vs model at the south SAF (Figure ), indicating a northeast dipping fault plane. The highest velocities are observed in the Peninsular Ranges, and a sharp velocity contrast from west to east at greater depth (7–15 km; white vertical line in Figure ) that corresponds to the Hemet stepover (Marliyani et al, ) is observed much clearly in the final model. Velocity contrasts across major faults (e.g., SAF and SJF) previously imaged in other tomography (e.g., Fang et al, ; Share et al, ) and fault zone head wave studies (Share & Ben‐Zion, , ) are observed clearly in the final Vs model.…”

Section: Shear Wave Velocity Inversionmentioning

confidence: 72%

Eikonal Tomography of the Southern California Plate Boundary Region

2019

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We use Eikonal tomography to derive phase and group velocities of surface waves for the plate boundary region in Southern California. Seismic noise data in the period range 2 and 20 s recorded in year 2014 by 346 stations with ~1‐ to 30‐km station spacing are analyzed. Rayleigh and Love wave phase travel times are measured using vertical‐vertical and transverse‐transverse noise cross correlations, and group travel times are derived from the phase measurements. Using the Eikonal equation for each location and period, isotropic phase and group velocities and 2‐psi azimuthal anisotropy are determined statistically with measurements from different virtual sources. Starting with the SCEC Community Velocity Model, the observed 2.5‐ to 16‐s isotropic phase and group dispersion curves are jointly inverted on a 0.05° × 0.05° grid to obtain local 1‐D piecewise shear wave velocity (Vs) models. Compared to the starting model, the final results have generally lower Vs in the shallow crust (top 3–10 km), particularly in areas such as basins and fault zones. The results also show clear velocity contrasts across the San Andreas, San Jacinto, Elsinore, and Garlock Faults and suggest that the San Andreas Fault southeast of San Gorgonio Pass is dipping to the northeast. Investigation of the nonuniqueness of the 1‐D Vs inversion suggests that imaging the top 3‐km Vs structure requires either shorter period (≤2 s) surface wave dispersion measurements or other types of data set such as Rayleigh wave ellipticity.

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Section: Shear Wave Velocity Inversionmentioning

confidence: 72%

Eikonal Tomography of the Southern California Plate Boundary Region

2019

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“…Most events in the central San Jacinto fault zone have directivities to the northwest, while most events around Cajon Pass and San Gabriel Mountain have directivities to the southeast. The observations imply that the ruptures tend to propagate in the direction of motion of slow sides of the imaged velocity contrasts (e.g., Allam & Ben‐Zion, ; Zigone et al, ; Share & Ben‐Zion, ; Share, Allam, et al, ). These results are generally consistent with expectations for dynamic rupture on a bimaterial interface (e.g., Ampuero & Ben‐Zion, ; Andrews & Ben‐Zion, ; Ben‐Zion, ; Brietzke & Ben‐Zion, ; Ranjith & Rice, ; Shlomai & Fineberg, ; Weertman, ).…”

Section: Discussionmentioning

confidence: 98%

Semiautomated Estimates of Directivity and Related Source Properties of Small to Moderate Southern California Earthquakes Using Second Seismic Moments

2020

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We develop a semiautomated method for estimating with second seismic moments the directivity, rupture area, duration, and centroid velocity of earthquakes. The method is applied to 41 southern California earthquakes with magnitude in the range 3.5-5.2 and provides stable results for 28 events. Apparent source time functions (ASTFs) of P and S phases are derived using deconvolution with three stacked empirical Green's functions (seGf). The use of seGf suppresses nongeneric source effects, improves the focal mechanism correspondence to the analyzed earthquakes, and typically allows inclusion of 5 to 15 more ASTFs compared with analysis using a single eGf. Most analyzed earthquakes in the Trifurcation area of the San Jacinto Fault have directivities toward the northwest, while events around Cajon Pass and San Gabriel Mountain tend to propagate toward the southeast. These results are generally consistent with predictions for dynamic rupture on bimaterial interfaces associated with the imaged velocity contrasts in the area. The second moment inversions also provide constraints on the upper and lower bounds of rupture areas in our data set. Stress drops and uncertainties are estimated for elliptical ruptures using the derived characteristic rupture length and width. The semiautomated second moment method with seGfs can be used for routine application to moderate earthquakes in locations with good station coverage.

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“…(2004) propose that the geometry and path of the present‐day SJF was dictated by a preexisting physical property contrast and that earthquakes on the fault continue to nucleate along this discontinuity. Detailed seismic imaging studies show that the main strike‐slip faults in Southern California are associated with prominent lithology contrasts (e.g., Fang et al., 2016; Qiu et al., 2019; Share & Ben‐Zion, 2016, 2018; Share et al., 2019). Here, we take this concept of inheritance further and propose that the Southern California region contains a pervasive rock fabric throughout the lithosphere.…”

Section: Discussion: the Importance Of Fault And Fabric Reactivation mentioning

confidence: 99%

Tectonic Inheritance With Dipping Faults and Deformation Fabric in the Brittle and Ductile Southern California Crust

et al. 2020

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Plate motions in Southern California have undergone a transition from compressional and extensional regimes to a dominantly strike‐slip regime in the Miocene. Strike‐slip motion is most easily accommodated on vertical faults, and major transform fault strands in the region are typically mapped as near vertical on the surface. However, some previous work suggests that these faults have a dipping geometry at depth. We analyze receiver function arrivals that vary harmonically with back azimuth at all available broadband stations in the region. The results show a dominant signal from contrasts in dipping foliation as well as dipping isotropic velocity contrasts from all crustal depths, including from the ductile middle to lower crust. We interpret these receiver function observations as a dipping fault‐parallel structural fabric that is pervasive throughout the region. The strike of these structures and fabrics is parallel to that of nearby fault surface traces. We also plot microseismicity on depth profiles perpendicular to major strike‐slip faults and find consistently NE dipping features in seismicity changing from near vertical (80–85°) on the Elsinore Fault in the Peninsular Ranges to 60–65° slightly further inland on the San Jacinto Fault to 50–55° on the San Andreas Fault. Taken together, the dipping features in seismicity and in rock fabric suggest that preexisting fabrics and faults may have acted as strain guides in the modern slip regime, with reactivation and growth of strike‐slip faults along northeast dipping fabrics both above and below the brittle‐ductile transition.

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A Bimaterial Interface Along the Northern San Jacinto Fault Through Cajon Pass

Cited by 14 publications

References 63 publications

Eikonal Tomography of the Southern California Plate Boundary Region

Eikonal Tomography of the Southern California Plate Boundary Region

Semiautomated Estimates of Directivity and Related Source Properties of Small to Moderate Southern California Earthquakes Using Second Seismic Moments

Tectonic Inheritance With Dipping Faults and Deformation Fabric in the Brittle and Ductile Southern California Crust

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