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Ge277

Ge277. Shengji Wei 2011/Feb./17. From previous seminar : Features of ductile shear zone. Thatcher, JGR, 1998. Outline. Travel time tomographic results cross SAF at Parkfield ( Roecker et. al.,2004).

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Ge277

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  1. Ge277 ShengjiWei 2011/Feb./17

  2. From previous seminar :Features of ductile shear zone Thatcher, JGR, 1998

  3. Outline • Travel time tomographic results cross SAF at Parkfield (Roecker et. al.,2004). • Tomographic and SKS splitting (anisotropy) studies along the AltynTagh Fault in Tibet (Wittlingeret. al., 1998; Herquel et. al., 1999). • Receiver function study cross SAF at Southern California(Zhu, 2000).

  4. Roecker et. al., 2004 (GRL) 686 earthquakes, 102 shots SAF 44530 P-wave, 47546 S-wave 903 Gravity data points SAFOD Min Grid Size=200m

  5. While Vp>6.0km/s Inversion Scheme: Smoothed by Polynomial While 5.5<Vp<6.0km/s Gravity inversion is not stable, because gravity is affected by density of every element, thus being much more underdetermined. So the inversion encourage the model to be close to the starting model which fits the arrival time best. While Vp<5.5km/s Arrival time only Arrival time + Gravity

  6. Low Vp and high Vp/Vs in the shear zone Fit both gravity and arrival time SAF Fit arrival time data Shelly, 2010, Nature

  7. Wittlinger et al. 1998, Science Longest active strike slip fault (1800km) of Asia 30 stations, 1995~1996, profile length 350km 3946 P-wave arrivals,

  8. Tomographic result The ATF is not restricted to the crust but controls at lithospheric scale.

  9. Sensitivity Test

  10. Herquel et. al. 1999, GRL SV: In the great circle plane Due to the Lattice Preferred Orientation of crystal in a single upper mantle layer, with horizontal fast direction Comes up almost vertically fast direction relative to the fault strike, time delay

  11. SKS splitting cross ATF 0.5 s 1.0 s Whether some of the faults that affect the crust extend downwards into the mantle as shear zones?

  12. Angle Relative to the ATF/ Time Delay vs. Distance Away from ATF

  13. Conclusion • Rapid swing of FPD(fast polarization direction) are observed across ATF. • From a azimuth of ~110degree in Qaidam Basin to a azimuth of ~60degree in the Altyn mountains. • The swing occurs in a short distance range(40km). • Consistent with tomographic study in the same region(low Vp anomalies at 140km).

  14. Basic method of receiver function • Part of the P waves signals incident to a discontinuity in the crust or upper mantle will be converted to S waves (Ps), that arrive at the station within the P wave coda directly after the direct P wave, the time separation between Ps and P can be used to estimate crustal thickness.

  15. Receiver function is obtained by removing the source time function from raw teleseismic records using deconvolution Vertical Radial

  16. For one M6.1 Earthquake

  17. The SAF and Eastern Californian Shear Zone extend through the entire crust. The Mohoupwarps under the San Gabriel Mt. indicates the mountain ranges were lifted entirelyas a result of horizontal compression

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