The Seismogenic Thickness of the Southern California Crust

Nazareth, Julie J.; Hauksson, Egill

doi:10.1785/0120020129

Cited by 97 publications

(91 citation statements)

References 40 publications

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“…The depth to the bottom of the upper crust is set to 15 km west of the SJF and tapers linearly to the lower extension of the SAF at a depth of 10 km, which then tapers to 13 km depth to the east of the SAF. This upper crust depth variation is similar to that used by Fay and Humphreys [2005] in their earthquake cycle modeling, is based on the seismic tomography model of Lin et al [2007], and is comparable to the seismogenic depths estimated for these fault segments [Nazareth and Hauksson, 2004]. Except in the region between the SJF and SAF faults, the depth to the Moho (lower crust-upper mantle boundary) is set to 30 km on the basis of the Moho depths of Yan and Clayton [2007].…”

Section: Model Setupsupporting

confidence: 66%

“…South of the Santa Rosa mountains no clear evidence exists for structural continuity between the Clark and Superstition Hills faults in a region of soft deforming sediments in the Borrego Badlands Kirby et al, 2007]. This is also an area that has relatively low seismicity [Nazareth and Hauksson, 2004;Lin et al, 2007]. Fialko [2006] preferred a model in which the entire strain accumulation on the SJF fault system was resolved on the most recently active eastern strand, and is consistent with the partitioning of the slip rates in the SJF system we found when equally weighting the InSAR and GPS data (Figure 9b).…”

Section: Saf Dip and Sjf Active Branchmentioning

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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Section: Model Setupsupporting

confidence: 66%

Section: Saf Dip and Sjf Active Branchmentioning

confidence: 99%

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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“…Our scaling is based on seismogenic depth H being fixed. Observations of seismicity along major faults suggest, however, it can vary along-strike [Nazareth and Hauksson, 2004]. To test the generality of our scaling relation, we have extended our analysis to include a seismogenic depth varying alongstrike H(x) = H 0 + (x) and examined the impact of varying H(x) in the scaling relations.…”

Section: Discussionmentioning

confidence: 99%

“…In short, while substantial coseismic slip below the seismogenic layer has not been directly observed, it has also not been ruled out by observations. Converting to moment-area scaling, we continue to examine only the seismogenic rupture lengths and area, since the actual downdip widths W of ruptures remain difficult to observe seismologically, whereas the seismogenic depth H can be constrained by seismicity [Nazareth and Hauksson, 2004]. Then, for seismogenic area A, and moment M for now just that associated with that area,…”

Section: Introductionmentioning

confidence: 99%

Constant Stress Drop from Small to Great Earthquakes in Magnitude-Area Scaling

Shaw¹

2009

Bulletin of the Seismological Society of America

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Earthquakes span a tremendous range of scales, more than 5 orders of magnitude in length. Are earthquakes fundamentally the same across this huge range of scales, or are the great earthquakes somehow different from the small ones? We show that a robust scaling law seen in small earthquakes, with stress drops being independent of earthquake size, indeed holds for great earthquakes as well. The simplest hypothesis, that earthquake stress drops are constant from the smallest to the largest events, combined with a more thorough treatment of the geometrical effects of the finite seismogenic layer depth, gives a new magnitude area scaling which matches the data well, and better over the whole magnitude range than the currently used scaling laws which have nonconstant stress drop scaling. This has significant implications for earthquake physics and for seismic hazard estimates.

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“…A special version of the CFM, in which the triangular surfaces of the original CFM were converted to rectangular patches, was developed for this purpose (see Data and Resources section). The lower seismogenic depths in CFM are from the maximum depth of relocated background seismicity, following Nazareth and Hauksson (2004). The southern San Andreas was repartitioned into ten sections: the Parkfield, Cholame, Carrizo, Big Bend, Mojave north, Mojave south, San Bernardino north, San Bernardino south, San Gorgonio-Garnet Hill, and Coachella (Fig.…”

Section: Fault Section Databasementioning

confidence: 99%

Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2)

Field

Dawson

Felzer

et al. 2009

Bulletin of the Seismological Society of America

269

183

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The 2007 Working Group on California Earthquake Probabilities (WGCEP, 2007) presents the Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2). This model comprises a time-independent (Poisson-process) earthquake rate model, developed jointly with the National Seismic Hazard Mapping Program and a time-dependent earthquake-probability model, based on recent earthquake rates and stress-renewal statistics conditioned on the date of last event. The models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular, extensible Open Seismic Hazard Analysis framework. The rate model satisfies integrating measures of deformation across the plate-boundary zone and is consistent with historical seismicity data. An overprediction of earthquake rates found at intermediate magnitudes (6:5 ≤ M ≤ 7:0) in previous models has been reduced to within the 95% confidence bounds of the historical earthquake catalog. A logic tree with 480 branches represents the epistemic uncertainties of the full time-dependent model. The mean UCERF 2 time-dependent probability of one or more M ≥ 6:7 earthquakes in the California region during the next 30 yr is 99.7%; this probability decreases to 46% for M ≥ 7:5 and to 4.5% for M ≥ 8:0. These probabilities do not include the Cascadia subduction zone, largely north of California, for which the estimated 30 yr, M ≥ 8:0 time-dependent probability is 10%. The M ≥ 6:7 probabilities on major strike-slip faults are consistent with the WGCEP (2003) study in the San Francisco Bay Area and the WGCEP (1995) study in southern California, except for significantly lower estimates along the San Jacinto and Elsinore faults, owing to provisions for larger multisegment ruptures. Important model limitations are discussed.

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The Seismogenic Thickness of the Southern California Crust

Cited by 97 publications

References 40 publications

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

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

Constant Stress Drop from Small to Great Earthquakes in Magnitude-Area Scaling

Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2)

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