Mantle Heterogeneities and the SCEC Reference Three-Dimensional Seismic Velocity Model Version 3

Kohler, Monica D.

doi:10.1785/0120020017

Cited by 129 publications

(144 citation statements)

References 23 publications

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“…Purely passive upwelling in response to the extension and subsequent conductive cooling near the surface would not be expected to produce an anomaly in the asthenosphere, which should already follow an adiabatic gradient. The anomaly is more pronounced and distinct in our Rayleigh wave-derived S wave images than in most P wave tomographic studies [e.g., Kohler et al, 2003], suggesting that melt probably plays an important role in creating it, because melt may more strongly affect S than P velocity.…”

Section: Upwelling Beneath Salton Troughmentioning

confidence: 51%

Rayleigh wave phase velocities, small‐scale convection, and azimuthal anisotropy beneath southern California

Yang¹,

Forsyth²

2006

J. Geophys. Res.

143

192

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[1] We use Rayleigh waves to invert for shear velocities in the upper mantle beneath southern California. A one-dimensional shear velocity model reveals a pronounced lowvelocity zone (LVZ) from 90 to 210 km. The pattern of velocity anomalies indicates that there is active small-scale convection in the asthenosphere and that the dominant form of convection is three-dimensional (3-D) lithospheric drips and asthenospheric upwellings, rather than 2-D sheets or slabs. Several of the features that we observe have been previously detected by body wave tomography: these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern Sierra Nevada and Walker Lane region; sinking lithosphere beneath the southern Central Valley; upwelling beneath the Salton Trough; and downwelling beneath the Transverse Ranges. Our new observations provide better constraints on the lateral and vertical extent of these anomalies. In addition, we detect two previously undetected features: a high-velocity anomaly beneath the northern Peninsular Range and a low-velocity anomaly beneath the northeastern Mojave block. We also estimate the azimuthal anisotropy from Rayleigh wave data. The strength is $1.7% at periods shorter than 100 s and decreases to below 1% at longer periods. The fast direction is nearly E-W. The anisotropic layer is more than 300 km thick. The E-W fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms: pure shear in the lithosphere due to N-S tectonic shortening and simple shear in sublithosphere mantle due to mantle flow.

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Section: Upwelling Beneath Salton Troughmentioning

confidence: 51%

Rayleigh wave phase velocities, small‐scale convection, and azimuthal anisotropy beneath southern California

Yang¹,

Forsyth²

2006

J. Geophys. Res.

143

192

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“…We chose this constraint because the higher heat flow across the Salton Trough [Magistrale, 2002], more than likely translates to a weaker lower crust. Since these models are sensitive to the relaxation time (t m = h/m), there is a trade off between the viscosity and the shear modulus, and seismological studies suggest that shear modulus under the Salton Trough is higher than in the adjacent lower crust [Kohler et al, 2003;Lin et al, 2007].…”

Section: Modeling Resultsmentioning

confidence: 99%

“…We use a heterogeneous shear modulus model on the basis of the CVM3 velocity model [Kohler et al, 2003], and assume an elastic upper crust overlying a Maxwell viscoelastic lower crust and mantle. To fit the strong velocity gradients across the faults, and accounting for the different times since the last earthquakes on each of the faults, we require a high-viscosity (10 21 Pa s) lower crust and a lowerviscosity (10 19 Pa s) upper mantle.…”

Section: Discussionmentioning

confidence: 99%

“…2-D mesh shown in Figure 6. We assume a heterogeneous shear modulus distribution on the basis of the SVM3 seismic velocity model [Kohler et al, 2003;Fay and Humphreys, 2005]. Figure 4 shows a comparison between the analytic solution of Savage and Prescott [1978] and the FEM solution for unit elastic layer thickness H, a lower homogeneous viscosity of 10 19 Pa s, and a homogeneous shear modulus of 3 Â 10 10 Pa. For modeling the southern San Andreas fault system, we use a finite element mesh consisting of three layers: an upper elastic crust overlying a viscoelastic lower crust, which in turn, is underlain by a viscoelastic upper mantle.…”

Section: Model Setupmentioning

confidence: 99%

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Southern San Andreas‐San Jacinto fault system slip rates estimated from earthquake cycle models constrained by GPS and interferometric synthetic aperture radar observations

Lundgren¹,

Hetland²,

Liu³

et al. 2009

J. Geophys. Res.

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[1] We use ground geodetic and interferometric synthetic aperture radar satellite observations across the southern San Andreas (SAF)-San Jacinto (SJF) fault systems to constrain their slip rates and the viscosity structure of the lower crust and upper mantle on the basis of periodic earthquake cycle, Maxwell viscoelastic, finite element models. Key questions for this system are the SAF and SJF slip rates, the slip partitioning between the two main branches of the SJF, and the dip of the SAF. The best-fitting models generally have a high-viscosity lower crust (h = 10 21 Pa s) overlying a lower-viscosity upper mantle (h = 10 19 Pa s). We find considerable trade-offs between the relative time into the current earthquake cycle of the San Jacinto fault and the upper mantle viscosity. With reasonable assumptions for the relative time in the earthquake cycle, the partition of slip is fairly robust at around 24-26 mm/a for the San Jacinto fault system and 16-18 mm/a for the San Andreas fault. Models for two subprofiles across the SAF-SJF systems suggest that slip may transfer from the western (Coyote Creek) branch to the eastern (Clark-Superstition hills) branch of the SJF from NW to SE. Across the entire system our best-fitting model gives slip rates of 2 ± 3, 12 ± 9, 12 ± 9, and 17 ± 3 mm/a for the Elsinore, Coyote Creek, Clark, and San Andreas faults, respectively, where the large uncertainties in the slip rates for the SJF branches reflect the large uncertainty in the slip rate partitioning within the SJF system.Citation: Lundgren, P., E. A. Hetland, Z. Liu, and E. J. Fielding (2009), Southern San Andreas-San Jacinto fault system slip rates estimated from earthquake cycle models constrained by GPS and interferometric synthetic aperture radar observations,

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“…The Los Angeles Basin is a typical example of this, where there have been many studies of its structure (Hauksson & Haase 1997;Fuis et al 2001;Süss & Shaw 2003;Tape et al 2009;Lee et al 2014;Shaw et al 2015), using data from both passive and active seismic experiments, as well as well-logs and reflection data from the oil industry. The culmination of these efforts has been the creation of a series of steadily improving Community Velocity Models (Kohler et al 2003;Plesch et al 2011;Shaw et al 2015), which are used among other things, in the simulation of ground motions from scenario earthquakes.…”

Section: Introductionmentioning

confidence: 99%

Higher-mode ambient-noise Rayleigh waves in sedimentary basins

Clayton

2016

Geophys. J. Int.

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S U M M A R YWe show that higher modes are an important component of high-frequency Rayleigh waves in the cross-correlations over sedimentary basins. The particle motions provide a good test for distinguishing and separating the fundamental from the first higher mode, with the fundamental mode having retrograde and the first higher mode having prograde motion in the 1-10 s period of interest. The basement depth controls the cut-off period of the first higher mode, which coincides with a rapid increase (over period) in the particle-motion ellipticity or H/V ratio of the fundamental mode. The strong higher mode we observed is not only due to the low-velocity sedimentary layer but also due to the noise sources with significant radial component such as the basin edge scattering. It is important to correctly identify the mode order when inverting the dispersion curves because misidentifying the higher mode as fundamental will lead to an anomalous high V SV velocity.

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Mantle Heterogeneities and the SCEC Reference Three-Dimensional Seismic Velocity Model Version 3

Cited by 129 publications

References 23 publications

Rayleigh wave phase velocities, small‐scale convection, and azimuthal anisotropy beneath southern California

Rayleigh wave phase velocities, small‐scale convection, and azimuthal anisotropy beneath southern California

Southern San Andreas‐San Jacinto fault system slip rates estimated from earthquake cycle models constrained by GPS and interferometric synthetic aperture radar observations

Higher-mode ambient-noise Rayleigh waves in sedimentary basins

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