IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic...
-
Upload
clarence-flowers -
Category
Documents
-
view
219 -
download
0
Transcript of IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic...
![Page 1: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/1.jpg)
IRIS Summer Intern Training CourseWednesday, May 31, 2006Anne Sheehan
Lecture 3: Teleseismic Receiver functionsTeleseismsEarth response, convolutionReceiver functions - basics, deconvolutionStacking receiver functions
receiver function ‘imaging’Complicated Earth
Dipping layersAnisotropic receiver functions
Applications & Examples - Himalaya, Western US
![Page 2: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/2.jpg)
Teleseisms used in Himalayan Receiver Function Study
![Page 3: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/3.jpg)
Want to deconvolve source and instrument response so we are just left
with the signal from structure
![Page 4: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/4.jpg)
![Page 5: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/5.jpg)
layer 2 vp, vs, density
layer 1 vp, vs, density
dt
amplitude
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
![Page 6: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/6.jpg)
unfortunately, incident P is not a nice simple bump:
need to remove these bits ...
... to isolate phases converted near station
source
station
![Page 7: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/7.jpg)
Receiver Function Construction• Convert seismogram from vertical, NS,
EW components to vertical, radial, transverse components
SourceReceiver
Wave propagation direction
SH: Transverse
SV: Radial
P wave compression
Surface
zy
X
![Page 8: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/8.jpg)
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:
![Page 9: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/9.jpg)
Linear Systems and Fourier Analysis
• Recall that for a linear system:
Source Signal: x(t)
Linear System: Response f(t)
Output: y(t) = x(t)*f(t) Y( ) = X( )F( )
Note: * means convolved, not multiplied!
![Page 10: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/10.jpg)
Linear Systems and Fourier Analysis
• Deconvolution is the inverse of CONVOLUTION
![Page 11: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/11.jpg)
Linear Systems and Fourier Analysis
![Page 12: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/12.jpg)
Teton Gravity Research&
Warren Millerpresent:
Craig Jones' new radical
receiver function movie
![Page 13: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/13.jpg)
A single receiver function - hard to interpret
time
ampl
itud
e
one receiver function per earthquake-function of slowness (incidence angle)-function of backazimuth (unless flat layered isotropic case)
![Page 14: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/14.jpg)
receiver functions are sensitive to discontinuity structure
![Page 15: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/15.jpg)
midcrustal conversion
"moveout plot":sort receiverfunctions byincidence angle(slowness)
station ILAM(Nepal)
radial receiver functionsbinned by slowness
direct P
Moho conversion
Schulte-Pelkum et al., 2005
![Page 16: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/16.jpg)
Moho ~70km
Tibet station
![Page 17: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/17.jpg)
arrival time/polarity variation with backazimuth(corrections for slowness + elevation applied)
azimuthal variation
![Page 18: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/18.jpg)
highly coherent transverse componentreceiver functions
transverse components
![Page 19: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/19.jpg)
attempt at a standard moveout plot for narrow azimuthal range
depth of modelleddiscontinuity(km)
multiples
![Page 20: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/20.jpg)
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
![Page 21: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/21.jpg)
stack along profile (red):
![Page 22: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/22.jpg)
Schulte-Pelkum et al., 2005
![Page 23: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/23.jpg)
but where is the decollement?
![Page 24: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/24.jpg)
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
-
F() = f(t)e-iwtdt-
Fourier transform
inverse Fourier transform
![Page 25: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/25.jpg)
Receiver Function Constructionafter Langston, 1979 and Ammon, 1991
• In the earth, the source signalsource signal is convolved with the earth’s responseearth’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
![Page 26: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/26.jpg)
Receiver Function Construction
• This is analogous to the form d = Gm
Theoretical Displacement Response for a P plane wave
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)
Displacement
Response
Instrument
Impulse
Response
Source
Time
Function
Structure
Impulse
Response
(Receiver Function)
![Page 27: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/27.jpg)
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)
![Page 28: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/28.jpg)
Receiver Function Construction
• In the frequency domain, Er and Et can be simply calculated
• this implies that Dv(t)*Er(t) = Dr(t)
Er() = Dr() = Dr()
I()S() Dv()
Et() = Dt() = Dt()
I()S() Dv()
![Page 29: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/29.jpg)
Receiver Function Construction
P SV
incident: steep P
mostly on vertical component
converted phase: SV (in plane)
mostly on radial component
with dipping interface with anisotropic layer
Out of plane S conversions
(on radial and transverse components)
![Page 30: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/30.jpg)
synthetic data
Schulte-Pelkum et al., 2005
![Page 31: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/31.jpg)
Azimuthal difference stacking
flip polarityof all receiverfunctions incidentfrom northerlybackazimuthsbefore stacking
![Page 32: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/32.jpg)
-> new interface shows up in stack
Schulte-Pelkum et al., 2005
![Page 33: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/33.jpg)
interface found with azimuthal difference stack has good match with INDEPTH decollementfound anisotropy suggests ductile shear deformation at depth
Schulte-Pelkum et al., 2005
![Page 34: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/34.jpg)
![Page 35: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/35.jpg)
incident: steep Pmostly 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
P
SV
![Page 36: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/36.jpg)
Receiver function profiles across the Western United States
Gilbert & Sheehan, 2004
![Page 37: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/37.jpg)
Western United States crustal thicknesses from receiver functions
Gilbert & Sheehan, 2004
![Page 38: IRIS Summer Intern Training Course Wednesday, May 31, 2006 Anne Sheehan Lecture 3: Teleseismic Receiver functions Teleseisms Earth response, convolution.](https://reader036.fdocuments.in/reader036/viewer/2022062309/5697bf8b1a28abf838c8af30/html5/thumbnails/38.jpg)
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