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

## Presentation on theme: "Accommodation space, Coluvial wedge. Even in this image, throw is hard to interpret however, there is still geologic insight to be gained. Surface expression."— Presentation transcript:

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

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.

Types of seismic events -Reflections -Direct Waves -Refractions -Surface Waves Many adaptations are from: Chris Liner’s book: Elements of 3D Seismology, 2004. Also see http://www.geol.lsu.edu/jlorenzo/ReflectSeismol13/Syllabus.htmhttp://www.geol.lsu.edu/jlorenzo/ReflectSeismol13/Syllabus.htm http://www.geol.lsu.edu/jlorenzo/PetroleumSeismology7900.2S14/Syllabus.html

Ross Sea, Antarctica, 2003

Direct water arrival Ross Sea, Antarctica, 2003

Normal Moveout x T Hyperbola:

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

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

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 ….

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

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

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

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

#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

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

What can we tell from the relative shape of the hyperbola? Increasing velocity (m/s) Increasing thickness (m) 1000 3000 50 250

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

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

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”

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

Calama, Chile, 2008

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)

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)

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

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

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

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

Refractions (mainly) and reflections Calama, Chile, 2008

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

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

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

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

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

Vinterval from Vrms Dix, 1955

Vrms V1 V2 V3 Vrms < Vinterval

Vinterval from Vrms

Primary seismic events x T

x T

x T

x T

Multiples and Primaries x T M1 M2

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

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

+ + = Stacking improves S/N ratio

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

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

Interpretation Baton Rouge Fault, 1999 V.E.~1, 300 m horizontal extent Two-waytraveltime (ms) 20002003(Elliott, 2011)

Interpretation-V1.0 IRIS 2012 SP 11999 Two-waytraveltime (ms) ~100m

Interpretation-V1.0 IRIS 2012 SP 11999 Two-waytraveltime (ms) ~100m

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./

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

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