Using Vertical Rock Uplift Patterns to Constrain the Three-Dimensional Fault Configuration in the Los Angeles Basin

Meigs, Andrew; Cooke, Michele L.; Marshall, S. T.

doi:10.1785/0120060254

Cited by 19 publications

(33 citation statements)

References 67 publications

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“…Previous Poly3D models have constrained the geometry of active faulting in southern California by comparing the model results to uplift patterns (Meigs et al, 2008;Cooke and Dair, 2011) and fault slip rates (e.g., Marshall et al, 2008;Cooke and Dair, 2011). Boundary-element method investigations of alternative fault confi gurations (e.g., Griffi th and Cooke, 2004;Marshall et al, 2008;Meigs et al, 2008;Dair and Cooke, 2009;Herbert et al, 2014) demonstrate that the three-dimensional fault geometry and connectivity exhibit fi rst-order effects on the distribution of deformation within these fault systems, including uplift patterns (Meigs et al, 2008;Cooke and Dair, 2011).…”

Section: Model Setupmentioning

confidence: 99%

“…Boundary-element method investigations of alternative fault confi gurations (e.g., Griffi th and Cooke, 2004;Marshall et al, 2008;Meigs et al, 2008;Dair and Cooke, 2009;Herbert et al, 2014) demonstrate that the three-dimensional fault geometry and connectivity exhibit fi rst-order effects on the distribution of deformation within these fault systems, including uplift patterns (Meigs et al, 2008;Cooke and Dair, 2011). Consequently, changes in fault geometry along the Coachella Valley segment of the San Andreas fault, and the inclusion of secondary faults in Indio and Mecca Hills, may exert a substantial infl uence on uplift within the region.…”

Section: Model Setupmentioning

confidence: 99%

“…that are impor-tant on longer time scales within folds and are not captured by elastic modeling. Consequently, as with previous models of uplift rate patterns (Meigs et al, 2008), we compare the pattern of uplift rates from these models to the geologic patterns and are not concerned with matching absolute uplift rates.…”

Section: Model Setupmentioning

confidence: 99%

“…Previous mechanical modeling has demonstrated that complex fault geometry exerts a primary control on deformation (e.g., Marshall et al, 2008;Meigs et al, 2008). In southern California, plate interactions and fault structure are complex ( Fig.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of uplift patterns to dip of the San Andreas fault in the Coachella Valley, California

2014

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Three-dimensional mechanical simulations of the San Andreas fault system within the Coachella Valley in southern California produce deformation that matches geologic observations and demonstrate the firstorder impact of fault geometry on uplift patterns. To date, most models that include the Coachella Valley segment of the San Andreas fault have assumed a vertical orientation for this fault, but recent studies of seismicity and geodetically observed strain suggest that this segment of the fault may dip 60°-70° to the northeast. We compare models with varied geometry along this segment of the fault and evaluate how well they reproduce observed uplift patterns in the Mecca Hills and Coachella Valley. Incorporating wellconstrained fault geometry in regional models will provide a more accurate understanding of active faulting in southern California, which is critical for rupture and hazard modeling that is used to identify regions most susceptible to earthquake damage.We have tested three boundary-element method models for the active geometry of the Coachella Valley segment of the San Andreas fault: one contains a vertical Coachella segment, the second contains a northeast ~65° dipping Coachella segment, and the fi nal alternative contains a vertical Coachella segment plus a subparallel northeast-dipping fault at depth. This fi nal model honors the geometric interpretation of seismicity from the Southern California Earthquake Center Community Fault Model version 4.0. The models containing vertical Coachella Valley segments both produce uplift between the San Andreas and San Jacinto faults that is more uniformly distributed than geologic observations suggest, and these models fail to produce uplift in the Mecca Hills. The dipping model produces tilting of the Coachella Valley consistent with geologic observations of tilting between the San Jacinto and San Andreas faults. The dipping model also produces relative subsidence southwest of the fault and localized uplift in the Mecca Hills that better match the geologic observations. These results suggest that the active Coachella Valley segment of the San Andreas fault dips 60°-70° to the northeast.

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Section: Model Setupmentioning

confidence: 99%

Section: Model Setupmentioning

confidence: 99%

Section: Model Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sensitivity of uplift patterns to dip of the San Andreas fault in the Coachella Valley, California

2014

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“…An alternative approach to modeling interseismic deformation is to use geodetic data to determine a regional strain or shortening rate and then use the regional strain rate to drive deformation in a forward mechanical model [ Cooke and Marshall , ; Cooke and Dair , ; Dair and Cooke , ; Herbert and Cooke , ; Marshall et al ., , ; Meigs et al ., ]. For example, using mechanical models of the western Transverse Ranges, Marshall et al .…”

Section: Existing Interseismic Deformation Models Of the Western Tranmentioning

confidence: 99%

Fault slip rates and interseismic deformation in the western Transverse Ranges, California

2013

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[1] To better constrain fault slip rates and patterns of interseismic deformation in the western Transverse Ranges of southern California, we present results from analysis of GPS and interferometric synthetic aperture radar (InSAR) data and three-dimensional mechanical and kinematic models of active faulting. Anthropogenic motions are detected in several localized zones but do not significantly affect the vast majority of continuous GPS site locations. GPS measures contraction rates across the Ventura Basin of~7 mm/yr oriented west-northwest with rates decreasing to the west and east. The Santa Barbara channel is accommodating~6.5 mm/yr in the east and~2.5 mm/yr in the western portions of N/S contraction. Inversion of horizontal GPS velocities highlights a zone of localized fast contraction rates following the Ventura Basin. Using a mechanical model driven by geodetically calculated strain rates, we show that there are no significant discrepancies between short-term slip rates captured by geodesy and longer-term slip rates measured by geology. Mechanical models reproduce the first-order interseismic velocity and strain rate patterns but fail to reproduce strongly localized contraction in the Ventura Basin due to the inadequate homogeneous elastic properties of the model. Existing two-dimensional models match horizontal rates but predict significant uplift gradients that are not observed in the GPS data. Mechanical models predict zones of fast contraction in the Santa Barbara channel and offshore near Malibu, suggesting that offshore faults represent a significant seismic hazard to the region. Furthermore, many active faults throughout the region may produce little to no interseismic deformation, making accurate seismic hazard assessment challenging.

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Influence of fault connectivity on slip rates in southern California: Potential impact on discrepancies between geodetic derived and geologic slip rates

2014

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Along the San Bernardino strand of the San Andreas fault (SAF) and across the eastern California shear zone (ECSZ), geologic slip rates differ from those inverted from geodetic measurements, which may partly be due to inaccurate fault connectivity within geodetic models. We employ three-dimensional models that are mechanically compatible with long-term plate motion to simulate both fault slip rates and interseismic surface deformation. We compare results from fault networks that follow mapped geologic traces and resemble those used in block model inversions, which connect the San Jacinto fault to the SAF near Cajon Pass and connect distinct faults within the ECSZ. The connection of the SAF with the San Jacinto fault decreases strike-slip rates along the SAF by up to 10% and increases strike-slip rates along the San Jacinto fault by up to 16%; however, slip rate changes are still within the large geologic ranges along the SAF. The insensitivity of interseismic surface velocities near Cajon Pass to fault connection suggests that inverse models may utilize both an incorrect fault geometry and slip rate and still provide an excellent fit to interseismic geodetic data. Similarly, connection of faults within the ECSZ produces 36% greater cumulative strike-slip rates but less than 17% increase in interseismic velocity. When using overconnected models to invert GPS for slip rates, the reduced off-fault deformation within the models can lead to overprediction of slip rates. While the nature of fault intersections at depth remains enigmatic, fault geometries should be chosen with caution in crustal deformation models.

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Using Vertical Rock Uplift Patterns to Constrain the Three-Dimensional Fault Configuration in the Los Angeles Basin

Abstract: Comparison of geologic uplift patterns with results of three-dimensional mechanical models provides constraints on the fault geometry compiled by the South-

Cited by 19 publications

References 67 publications

Sensitivity of uplift patterns to dip of the San Andreas fault in the Coachella Valley, California

Sensitivity of uplift patterns to dip of the San Andreas fault in the Coachella Valley, California

Fault slip rates and interseismic deformation in the western Transverse Ranges, California

Influence of fault connectivity on slip rates in southern California: Potential impact on discrepancies between geodetic derived and geologic slip rates

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