IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan

1. IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution Receiver functions - basics, deconvolution Stacking receiver functions receiver function ‘imaging’ Complicated Earth Dipping layers Anisotropic receiver functions Applications & Examples - Himalaya, Western US

2. Teleseisms used in Himalayan Receiver Function Study

3. Want to deconvolve source and instrument response so we are just left with the signal from structure

5. converted pulse: delay time dt depends on depth of interface and vp, vs of top layer amplitude depends on velocity contrast (mostly) and density contrast (weakly) at the interface converted arrival: "+" bump = bottom slow, top fast "-" bump = bottom fast, top slow layer 2 vp, vs, density layer 1 vp, vs, density dt amplitude

6. unfortunately, incident P is not a nice simple bump: station source ... to isolate phases converted near station need to remove these bits ...

7. Receiver Function Construction • Convert seismogram from vertical, NS, EW components to vertical, radial, transverse components Source Receiver Surface SH: Transverse z Wave propagation direction y P wave compression X SV: Radial

8. The magic step to isolate near-receiver converted phases via receiver function analysis: incident P appears mostly on the vertical component, converted S appears mostly on horizontal components. -> call the vertical component the "source" (it's as close as we're going to get to the true source function) and remove it from the horizontal components; what remains is close enough to the converted phases. how this works:

9. Linear Systems and Fourier Analysis • Recall that for a linear system:

10. Linear Systems and Fourier Analysis • Deconvolution is the inverse of CONVOLUTION

11. Linear Systems and Fourier Analysis

12. Teton Gravity Research & Warren Miller present: Craig Jones' new radical receiver function movie

13. A single receiver function - hard to interpret amplitude time • one receiver function per earthquake • function of slowness (incidence angle) • -function of backazimuth (unless flat layered isotropic case)

14. receiver functions are sensitive to discontinuity structure

15. "moveout plot": sort receiver functions by incidence angle (slowness) station ILAM (Nepal) radial receiver functions binned by slowness Moho conversion midcrustal conversion direct P Schulte-Pelkum et al., 2005

16. Tibet station Moho ~70km

17. azimuthal variation arrival time/polarity variation with backazimuth (corrections for slowness + elevation applied)

18. transverse components highly coherent transverse component receiver functions

19. attempt at a standard moveout plot for narrow azimuthal range multiples depth of modelled discontinuity (km)

20. common conversion point (CCP) stacking scale time to depth along incoming ray paths with an assumed velocity model stack all receiver functions within common conversion point bin

21. profile (red): stack along

22. Schulte-Pelkum et al., 2005

23. but where is the decollement?

24. Linear Systems and Fourier Analysis • Using Fourier analysis, deconvolution of linear system responses becomes a very simple problem of division in the frequency domain • Solution in the frequency domain is converted to a solution in the time domain using the Fourier transform  f(t) = 1 F()eiwtd 2  Fourier transform -   inverse Fourier transform F() = f(t)e-iwtdt -

25. Receiver Function Constructionafter Langston, 1979 and Ammon, 1991 • In the earth, the source signal is convolved with the earth’s response • We want to extract the information pertaining to the earth’s response, because it can tell us about the earth’s structure • We also have to worry about the instrument responses from our seismometers

26. Receiver Function Construction Theoretical Displacement Response for a P plane wave • This is analogous to the form d = Gm Dv(t) = I(t)*S(t)*Ev(t) (vertical) Dr(t) = I(t)*S(t)*Er(t) (radial) Dt(t) = I(t)*S(t)*Et(t) (transverse) Instrument Impulse Response Structure Impulse Response (Receiver Function) Source Time Function Displacement Response

27. Receiver Function Construction • Assumption: using nearly vertically incident events, the vertical component approximates the source function convolved with the instrument response Dv(t) = I(t)*S(t)

28. Er() = Dr() = Dr() I()S() Dv() Et() = Dt() = Dt() I()S() Dv() Receiver Function Construction • In the frequency domain, Er and Et can be simply calculated • this implies that Dv(t)*Er(t) = Dr(t)

29. P SV Receiver Function Construction incident: steep P mostly on vertical component converted phase: SV (in plane) mostly on radial component Out of plane S conversions (on radial and transverse components) with dipping interface with anisotropic layer

30. synthetic data Schulte-Pelkum et al., 2005

31. Azimuthal difference stacking flip polarity of all receiver functions incident from northerly backazimuths before stacking

32. -> new interface shows up in stack Schulte-Pelkum et al., 2005

33. interface found with azimuthal difference stack has good match with INDEPTH decollement found anisotropy suggests ductile shear deformation at depth Schulte-Pelkum et al., 2005

35. out-of-plane S conversions (on radial and transverse components): incident: steep P mostly on vertical component P with dipping interface converted phase: SV (in plane) mostly on radial component SV with anisotropic layer

36. Receiver function profiles across the Western United States Gilbert & Sheehan, 2004

37. Western United States crustal thicknesses from receiver functions Gilbert & Sheehan, 2004

38. On-line resources: convolution animation: http://www-es.fernuni-hagen.de/JAVA/DisFaltung/convol.html Chuck Ammon's online receiver function tutorial: http://eqseis.geosc.psu.edu/~cammon/HTML/RftnDocs/rftn01.html