Download presentation

Presentation is loading. Please wait.

Published byNikki Nightengale Modified about 1 year ago

1
Accommodation space, Coluvial wedge. Even in this image, throw is hard to interpret however, there is still geologic insight to be gained. Surface expression of the fault

2
Goals A. Distinguish among the following IDEAL types of seismic arrivals: 1.Seismic reflections 2.Seismic Refractions 3.Surface Waves B. Learn to decide what can be a good plan to remove noise and enhance signal C. Learn not to be afraid to interpret, test, and reinterpret arrivals.

3
Types of seismic events -Reflections -Direct Waves -Refractions -Surface Waves Many adaptations are from: Chris Liner’s book: Elements of 3D Seismology, Also see

4
Ross Sea, Antarctica, 2003

5
Direct water arrival Ross Sea, Antarctica, 2003

6
Normal Moveout x T Hyperbola:

7
Hyperbola x y As x -> infinity, Y-> X. a/b, where a/b is the slope of the asymptote x asymptote

8
Reflection between a single layer and a half-space below P O X/2 h V1V1 Travel distance = ? Travel time = ?

9
Reflection between a single layer and a half-space below P O X/2 h V1V1 Travel distance = ? Travel time = ? Consider the reflecting ray……. as follows ….

10
Reflection between a single layer and a half-space below P O X/2 h V1V1 Travel distance = Travel time =

11
Reflection between a single layer and a half-space below Traveltime = (6)

12
Reflection between a single layer and a half-space below and D-wave traveltime curves asymptote Matlab code

13
#1 At X=0, T= 2h /V 1 Two important places on the traveltime hyperbola * T 0 =2h/V 1 h Matlab code

14
#1As X--> very large values, and X>>h, then (6) simplifies into the equation of straight line with slope dx/dT = V 1 (6) If we start with as the thickness becomes insignificant with respect to the source-receiver distance

15
By analogy with the parametric equation for a hyperbola, the slope of this line is 1/V 1 i.e. a/b = 1/V 1

16
What can we tell from the relative shape of the hyperbola? Increasing velocity (m/s) Increasing thickness (m)

17
“ Greater velocities, and greater thicknesses flatten the shape of the hyperbola, all else remaining constant ”

18
Reflections from a dipping interface #In 2-D Matlab code Direct waves 10 30

19
Reflections from a 2D dipping interface #In 2-D: “The apex of the hyperbola moves in the geological, updip direction to lesser times as the dip increases”

20
Types of seismic events -Reflections -Direct Waves -Refractions -Surface Waves

21
Calama, Chile, 2008

22
Processing Steps Read the data (Convert from SEG2 to SU, a variant of SEGY) Eliminate non-reflectors (Mute refractions) Eliminate non-reflectors (f-k surface waves) Improve resolution (Spike the data) Improve signal-to-noise ratio (Velocity analysis) Restore true dip and remove diffractions (Migrate) Interpret (at all times)

23
x (m) Two-way traveltime (s) f (1/s) k (wavenumber - 1/m) V h=inf (m/s) V = 1000 (m/s) V h=inf (m/s) V = 1000 (m/s) Eliminate non-reflectors (f-k surface waves)

24
F-k analysis of surface waves IRIS 2012, Socorro NM

25
F-k surface waves F-k filtering of surface waves IRIS 2012, Socorro NM

26
Improve resolution (“Spike the data”) Convolutional Earth Model

27
Steps in Spiking Deconvolution Calculate autocorrelation function (ACF) “Study” the width of the ACF Conduct inverse filtering using ACF

28
Refractions (mainly) and reflections Calama, Chile, 2008

29
Normal Moveout x T Hyperbola: Improve signal-to-noise ratio (Velocity analysis)

30
Normal Moveout x T “Overcorrected” Normal Moveout is too large Chosen velocity for NMO is too (a) large (b) small

31
Normal Moveout x T “Overcorrected” Normal Moveout is too large Chosen velocity for NMO is too small (a) large (b) small

32
Normal Moveout x T “Under corrected” Normal Moveout is too small Chosen velocity for NMO is (a) too large (b) too small

33
Normal Moveout x T “Under corrected” Normal Moveout is too small Chosen velocity for NMO is too large (a) too large (b) too small

34
Vinterval from Vrms Dix, 1955

35
Vrms V1 V2 V3 Vrms < Vinterval

36
Vinterval from Vrms

37
Primary seismic events x T

38
x T

39
x T

40
x T

41
Multiples and Primaries x T M1 M2

42
Conventional NMO before stacking x T NMO correction V=V(depth) e.g., V=mz + B M1 M2 “Properly corrected” Normal Moveout is just right Chosen velocity for NMO is correct

43
+ + = Improve signal-to-noise ratio (Stacking)

44
+ + = Stacking improves S/N ratio

45
+ = Semblance Analysis “Semblance” + X Twtt (s)

46
+ = Semblance Analysis + X Twtt (s) V3V3 V1V1 V2V2 V Peak energy

47
Interpretation Baton Rouge Fault, 1999 V.E.~1, 300 m horizontal extent Two-waytraveltime (ms) (Elliott, 2011)

48
Interpretation-V1.0 IRIS 2012 SP Two-waytraveltime (ms) ~100m

49
Interpretation-V1.0 IRIS 2012 SP Two-waytraveltime (ms) ~100m

50
Notes Create working directory structure Make sure you are in your home directory Run the following instructions $ cp /u/jlorenzo /Project_Variables.pm./ $ cp /u/jlorenzo/setenviron.bash./ $ cp /u/jlorenzo/IRIS2014_SocorroCanyonFault.pptx./ $ source setenviron.bash $ gedit Project_Variables.pm Modify Project_Variables.pm according to the following instructions: Change $HOME = ‘/u/jlorenzo’ to $HOME = ‘/u/”your_login_name” (Save and Exit) $ SetProject $cp./Project_Variables.pm IRIS2014/seismics/pl/Socorro/Z/1/ $cd IRIS2014/seismics/pl/Socorro/Z/1/ $cp -R /u/jlorenzo/IRIS2014/seismics/pl/Socorro/Z/1./

51
Notes Directory structure Home_directory IRIS2014/ geomaps/ well/ seismics/ /data /pl etc. /Socorro/Socorro /Z /Z /1/1 /su etc /libAll

Similar presentations

© 2016 SlidePlayer.com Inc.

All rights reserved.

Ads by Google