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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

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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.

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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

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Ross Sea, Antarctica, 2003

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Direct water arrival Ross Sea, Antarctica, 2003

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Normal Moveout x T Hyperbola:

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

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

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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 ….

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

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

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

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

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#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

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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

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

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

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

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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”

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

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Calama, Chile, 2008

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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)

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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)

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

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

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

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

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Refractions (mainly) and reflections Calama, Chile, 2008

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

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

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

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

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

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Vinterval from Vrms Dix, 1955

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Vrms V1 V2 V3 Vrms < Vinterval

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Vinterval from Vrms

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Primary seismic events x T

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x T

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x T

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x T

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Multiples and Primaries x T M1 M2

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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

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

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+ + = Stacking improves S/N ratio

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

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

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

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

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

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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./

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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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GG 450 April 16, 2008 Seismic Reflection 1.

GG 450 April 16, 2008 Seismic Reflection 1.

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