Quantifying simultaneous discrete and distributed deformation

Horsman, Eric; Tikoff, Basil

doi:10.1016/j.jsg.2004.08.001

Cited by 12 publications

(5 citation statements)

References 43 publications

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“…The rates chosen for these models vary widely, including 23-25 mm/ yr (Nadeau and Johnson, 1998;Murray et al, 2001) 26-29 mm/yr (Harris and Segall, 1987;Argus and Gordon, 2001); 30-33 mm/yr (Slawson and Savage, 1983;Jones and Wesnousky, 1992;Ben-Zion et al, 1993), and Ͼ33 mm/yr (Simpson et al, 1988;Thatcher and England, 1998;Bokelmann and Kovach, 2003;Horsman and Tikoff, 2005). Further, analysis of data from the same location can yield results consistent with either model presented above.…”

Section: Discussionmentioning

confidence: 88%

Thirty-Five-Year Creep Rates for the Creeping Segment of the San Andreas Fault and the Effects of the 2004 Parkfield Earthquake: Constraints from Alignment Arrays, Continuous Global Positioning System, and Creepmeters

Titus

DeMets

Tikoff

2006

Bulletin of the Seismological Society of America

137

132

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We present results from differential Global Positioning System (GPS) surveys of seven alignment arrays and four continuous GPS sites along the creeping segment of the San Andreas fault. Surveys of four alignment arrays from the central creeping segment yield 33-to 36-year average minimum slip rates of 21-26 mm/yr. These rates are consistent with previous alignment array surveys spanning a 10-year period and with rates determined by creepmeters, indicating approximate steadystate creep along the central creeping segment for at least 35 years. Motion between continuous GPS sites that span the central creeping segment is 28.2 ‫ע‬ 0.5 mm/yr for two sites that are 1 km apart and 33.6 ‫ע‬ 1 mm/yr for two sites that are 70 km apart. Slip rates therefore increase with distance from the creeping segment of the San Andreas fault. All rates reported here are significantly slower than the 39 ‫ע‬ 2 mm/yr rate predicted for motion between the Sierra Nevada-Great Valley block and the Pacific plate. Repeat surveys of three alignment arrays following the 2004 Parkfield earthquake demonstrate that its coseismic and short-term postseismic offsets decrease rapidly with distance from the epicenter, from 150 mm to 15 mm to Ͻ5 mm at respective distances of 9, 36, and 54 km to the northwest. Continuous GPS data confirm that little coseismic and postseismic slip occurred along the central creeping segment. Geodetic and geologic slip rates are compared and different models for the accommodation of transcurrent deformation across the creeping segment are discussed.

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Section: Discussionmentioning

confidence: 88%

Thirty-Five-Year Creep Rates for the Creeping Segment of the San Andreas Fault and the Effects of the 2004 Parkfield Earthquake: Constraints from Alignment Arrays, Continuous Global Positioning System, and Creepmeters

Titus

DeMets

Tikoff

2006

Bulletin of the Seismological Society of America

137

132

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“…Ramsy & Hubber 1983, pp. 283–292; Horsman & Tikoff 2005) or displacement fields (e.g. Wojtal 1989; Little 1996).…”

Section: Resultsmentioning

confidence: 99%

“…Since sampled points are used to monitor strain, estimated deformation in each cell (12 × 12 mm) may consist of the simultaneous discrete structures (e.g. thrusts) and distributed deformation (Horsman & Tikoff 2005).…”

Section: Resultsmentioning

confidence: 99%

Displacement fields and finite strains in a sandbox model simulating a fold-thrust-belt

Nilforoushan

Koyi

2007

Geophysical Journal International

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S U M M A R YA sandbox model consisting of two adjacent mechanically different decollements (frictional and viscous) loosely simulated the southeastern part of the Zagros fold-thrust-belt. Digital images of the model surface are used to coordinate passive markers on the surface and quantify displacement fields and estimate 2-D finite strains. These analyses show that, mapped in a fixed coordinate system, the deformation front propagates at different rates above the two decollements. Strain analysis of the model surface at different stages of deformation also shows that cumulative strain is more heterogeneous above the viscous decollement where strain domains are separated by fault zones. Maps of displacement fields, finite strain ellipses and dilatation also differ in character above the two decollements. Displacements above a viscous decollement decrease gradually towards the foreland, whereas they decrease sharply in front of the frontal thrust above the frictional decollement. Our analyses also show that the estimated finite strain depends not only on the density of the marker points chosen for the analysis, but also their initial distribution relative to the structures. This comparison shows that marker density limits measuring the actual strains in a heterogeneously deforming fold-thrustbelt and marker density and distribution have a strong impact on the strain analysed in nature. The similarity of our model with nature is examined with recent GPS study in the Zagros fold-thrust-belt (SW Iran) and shows, similar to the model results, that a weak salt decollement causes divergent movement in the sedimentary cover in SE Zagros.

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“…[2] A more precise understanding of the fundamental physics that control the long-term failure of frictionally sliding continental upper crust in diffuse plate boundary zones requires linking tectonic fault regimes with geodynamic estimates of upper crustal strength. For instance, a major question unresolved in the fault mechanics community is whether or not the San Andreas Fault is a weak or strong fault [e.g., Brune et al, 1969;Mount and Suppe, 1987;Zoback et al, 1987;Lachenbruch and Sass, 1992;Zoback and Beroza, 1993;Scholz, 2000;Saffer et al, 2003;Scholz and Hanks, 2004;Townend and Zoback, 2004;Horsman and Tikoff, 2005;d'Alessio et al, 2006]. Ambiguity about the relative degree of friction on this well-studied major transform fault suggests that frictional strength on faults of all fault types in plate boundary settings needs reexamination.…”

Section: Introductionmentioning

confidence: 99%

Evidence of long‐term weakness on seismogenic faults in western North America from dynamic modeling

Klein¹,

Flesch²,

Holt³

et al. 2009

J. Geophys. Res.

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[1] We investigate the long-term strength of faults within the plate boundary zone of western North America by quantifying the depth-integrated deviatoric stress field acting within the seismogenic portion of the crust. Forcings in the depth-integrated force balance equations are the horizontal gradients in gravitational potential energy per unit area (GPE). Seismic velocity data define the densities we use to determine GPE. We also solve for stress field boundary conditions that, when added to the contribution from GPE differences, provides a best fit to stress indicators. We estimate that the long-term depth-integrated total stress differences within the approximately 20 km thick seismogenic layer are of the order of 0.1-1.4 Â 10 12 N m À1 . Using these stress differences as a proxy for depth integrals of fault strength within the actively deforming regions, we infer that the long-term values of coefficients of friction on faults within the Basin and Range of Nevada and Utah, and most of California, are 0.1-0.2 under long-term hydrostatic pore pressure conditions. We test the sensitivity of these results by considering a range of maximum depths of integration. We show that for depths of integration in excess of 20 km below sea level, there is diminishing contribution to the depth-integrated stress differences, and by proxy depth-integrated fault strength. This is consistent with a brittle-ductile transition in the plate boundary zone at depths less than 20 km below sea level, and with a weaker lower crust.

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Quantifying simultaneous discrete and distributed deformation

Cited by 12 publications

References 43 publications

Thirty-Five-Year Creep Rates for the Creeping Segment of the San Andreas Fault and the Effects of the 2004 Parkfield Earthquake: Constraints from Alignment Arrays, Continuous Global Positioning System, and Creepmeters

Thirty-Five-Year Creep Rates for the Creeping Segment of the San Andreas Fault and the Effects of the 2004 Parkfield Earthquake: Constraints from Alignment Arrays, Continuous Global Positioning System, and Creepmeters

Displacement fields and finite strains in a sandbox model simulating a fold-thrust-belt

Evidence of long‐term weakness on seismogenic faults in western North America from dynamic modeling

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