Stress modulation on the San Andreas fault by interseismic fault system interactions Jack Loveless and Brendan Meade, Geology, 2011

Transcription

1 Stress modulation on the San Andreas fault by interseismic fault system interactions Jack Loveless and Brendan Meade, Geology, 2011 A three step process: 1 - Assimilate plate boundary wide GPS data into a Western North America block model with microplate geometries in southern California derived from the CFM-R. 2 - Deconvolve the GPS velocity field into rotational and earthquake cycle components. Estimate fault slip rates independent of geologic estimates 3 - Calculate full stress tensor at depth in response to slip deficit across the three-dimensional fault system. The equilibrium equations are automatically satisfied and fault interactions are explicitly included.

2 Updating Meade and Hager (2005) GPS velocities Estimated fault slip rates A. GPS velocities B. Strike-slip rates m. 3 n N 32.5 N N 100 km mm/yr a. SAF Carrizo b. SAF WW-G c. SAF Mojave d. SAF San Bernardino e. SAF Indio f. SAF Imperial g. Imperial h. San Jacinto i. Elsinore j. White Wolf (WW) k. Garlock (G) West l. G Central m. Panamint Valley n. Death Valley o. Lockhart p. Calico-Blackwater q. Goldstone-Bullion r. Ludlow a. 31 b. 26 N j km k. -2 l. -4 c o. 6 p. 1 q. 7 d. 10 mm/yr i. 4 h. 14 r. 3 e. 24 f. 33 g N 32.5 N W 120 W W 115 W W 120 W W 115 W Figure 2. Block model constraints and results. A: Interseismic velocity field (McClusky et al., 2001; Shen et al., 2003; Hammond and Thatcher, 2005; Williams et al., 2006; McCaffrey et al., 2007; Plate Boundary Observatory network velocity field, relative to stable North America. Arrow length is uniform; speed is denoted by color. GPS global positioning system. B: Estimated strike-slip rates on GPS block-bounding data: faults McClusky from our reference et al. (2001); block model Shen given et by al. colored (2003); lines (right Hammond lateral is positive). and Thatcher Gray lines show (2005); block geometry, which is constructed by connecting faults with parameters specified by the Southern California Earthquake Center Rectilinear Community Fault Williams Model (Plesch et al. et al., (2006); 2007) (black McCaffrey lines). SAF San et al. Andreas (2007); fault. Plate Selected Boundary faults are labeled Observatory with average network slip rate (rounded to nearest mm/yr). Full list of slip rates is in Table DR1 (see footnote 1). Figure constructed using Generic Mapping Tools (Wessel and Smith, 1998). Fault system geometry: Rectilinear Community Fault Model (Plesch et al., 2007)

3 Local fault stressing rates are affected by all faults Shear stress rate (τ/τ max. ) τ /τ 1 max. τ 2 /τ max. τ TOT /τ max. X /d 1 X /d 2 W/d Strike normal position (X/d ) B Fault separation (W/d )

4 J2 at 11 km depth latitude log 10 J longitude

5 J2 at 11 km depth Negligible stressing on SAF north of Parkfield due to fact that it is creeping. Strain rate gradients are still high here. Patchy local maxima due to discontinuous representations of dipping faults latitude log 10 J Stressing rates localized along SAF and SJF. Locking depth variations matter longitude Maximum stresses at locking depth and decreasing toward surface