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, Also see
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)
“ 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”
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
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./