tramp.doc

实现地震射线追踪和反演的frotran程序

   supplied as an internal check to ensure that the correct rays 
   specified in the array ray  or the arrays amin and  amax have 
   been traced. This  ray code is  determined by the  program as 
   follows: the number to the left of the decimal  refers to the 
   deepest layer encountered by the ray; the number to the right 
   of the decimal will be one, unless (1) the  ray was reflected 
   upward from a layer boundary, in which case it will be two, or 
   (2) the ray traveled as a head wave, in which case it will be 
   three (assuming the ray was not reflected upward from a layer 
   boundary after traveling as a head wave).

Shot point located at depth: in  this case, the array ray  should 
   not contain ray codes corresponding to layers  above the shot 
   point.

Ray step length:  a very small  value of step  may not result  in 
   increased ray tracing accuracy due to round-off error

Ray changes direction: a ray traveling left to right  can reflect 
   or refract and change direction and travel right  to left, or 
   vice versa.

Terminating a ray:  if istop=0,  a ray  will be  traced until  it 
   encounters the top, bottom, left or right of the model, unless 
   it is reflected off the top of the model using nrbnd and rbnd.

Ray stopped warning: the warnings  which begin ray stopped -  are 
   included in  the  file  r1.out  directly before  the  summary  
   information for that ray is listed.

Failure of ray  search mode:  it is possible  that the  iterative 
   shooting/bisection algorithm used in the ray  search mode may 
   fail, or find  a limited range  of take-off angles  that only 
   sample a part of a  layer, if either (1) the  model has large 
   lateral variations, (2) the range of take-off angles defining 
   the desired ray group is very small, (3) the value of nsmax is 
   too small or stol is too large, or (4) it  is not possible to 
   trace the desired type of  rays through a particular  part of 
   the model (i.e., violates Snell's law). In any case, increase 
   the value of nsmax first and then decrease the  value of stol 
   if necessary and this should work (unless the problem is case 
   4). If this fails,  take-off angles can be  supplied manually 
   using ray=1.0 and  the arrays amin  and amax. Use  irays=1 to 
   see why the search mode is failing.

Travel  time-  and  amplitude-distance  curves:  join  successive  
   points of the same ray  code in the same ray  group. Prograde 
   and retrograde branches will be separated if ibreak=1.

Ray  search  mode  and  multiple  reflections:  for   ray  groups  
   specified by  L.2  in  the  array ray,  the  take-off  angles  
   determined in the search  mode will correspond to  rays which 
   reflect off the Lth  layer boundary only  and may or  may not 
   give rise to the multiple reflections specified  by nrbnd and 
   rbnd .

Integer code in the file tx.out: is used to identify  each travel 
   time to allow  for the appropriate  comparison with  the rays 
   traced  during  inversion.  It  will  begin  at   one  and  be  
   incremented one for each ray group if  itxout=1. In addition, 
   the integer will be  incremented by one  for a change  from a 
   prograde to retrograde branch or vice versa if ibreak=1. 

Laterally homogeneous  layer:  if  a  layer  boundary  is  to  be  
   horizontal or the upper or lower velocity of a layer is to be 
   constant, then only a single point is required in the velocity 
   model and it should be specified at an  x-coordinate equal to 
   xmin. If two or more points are required, then  the first and 
   last point must be specified at xmin and xmax, respectively.

Constant  velocity  layer:  to  specify  a  layer  with  constant  
   velocity, assign a  single upper layer  velocity at  xmin and 
   assign a lower layer velocity of zero at xmin.

Zero vertical velocity  gradient layer: to  specify a layer  with 
   zero vertical  velocity gradient,  assign one  or more  upper 
   layer velocities as usual and assign a lower layer velocity of 
   zero at xmin.

Zero velocity discontinuity across  layer boundary: to specify  a 
   layer boundary  with  no associated  velocity  discontinuity,  
   assign an upper layer velocity of zero at xmin  for the layer 
   directly beneath the boundary.

Head waves:  if  the  velocity  contrast  across  the  head  wave  
   boundary away from the critical point is zero or negative, the 
   angle of emergence from the boundary is 90 degree (grazing). Head 
   wave amplitudes will be incorrect if any part of the ray path 
   contains a reflection or conversion.

In-plane spreading/cubic spline: a  non-head wave ray group  must 
   consist of  at  least  two  rays to  calculate  the  in-plane  
   spreading. The slope  of the cubic  spline used  to calculate 
   the in-plane spreading may be sensitive to the number of rays 
   traced for  a particular  ray group  if the  model has  large 
   lateral variations; therefore, the number of rays traced will 
   determine the amount of lateral heterogeneity that is sampled.

Q attenuation: is calculated at a single frequency, omega, and is 
   applied    equally    at    all    frequencies,     i.    e.,    
   frequency-independent attenuation;  therefore,  there  is  no  
   waveform distortion due to dispersion.  This approximation is 
   valid for narrow-band data or if the  total attenuation along 
   any given ray path is not too large.

 
External plot routines: TRAMP is self-contained except  for the
   graphics calls inside the following CALCOMP or CALCOMP-like plot 
   routines: PLOTS, PLOT, NUMBER, SYMBOL, LINE, EMPTY, ERASE, PLOTND. 
   The file pltlib.f contains ALL these routines (and a few other 
   less important ones used by the graphics system where the 
   code was developed) and it will be necessary to replace the "call" 
   statements within each of these with their equivalents in the 
   local graphics package.

                           Array Sizes

The parameters specifying the size of all arrays within TRAMP are 
contained in the  file tramp.par  and may  be altered  to suit  a 
particular problem and memory requirements.

model layers - player

points defining a single layer boundary (must be a multiple of 10) 
   - ppcntr

points at which the upper or lower layer velocity is defined (must 
   be a multiple of 10) - ppvel

trapezoids within a layer - ptrap

shot points - pshot

ray codes for a single shot - prayf

ray groups for all shots combined - ptrayf

rays in a single group - pnrayf

rays reaching the surface (not including the search mode) - pray

points defining a single ray - ppray

intersections with model boundaries for a single ray - piray

reflecting boundaries for a single ray - prefl

reflecting boundaries for all ray groups - preflt

converting boundaries for a single ray - pconv

converting boundaries for all ray groups - pconvt

points defining smooth layer boundary or isovelocity contour - 
   pnsmth

trapezoids within which Poisson's ratio is modified - papois

velocity-depth profiles - pnvz

arrivals in a single seismogram - parriv

seismograms - pseis

                    Warning and Error Messages

The following is a list  and explanation of all possible  warning 
and error messages generated by TRAMP:

*** error  in velocity  model ***  - an  error in  the format  of 
   the velocity model in the file r.in or v.in has been detected. 
   One of the following problems exists:
      (1) the  x-coordinates  of a  boundary  or upper  or  lower 
         velocity have not been listed from left to right
      (2) the  x-coordinate  of the  first  or last  point  of  a 
         boundary or upper or lower velocity (comprised of two or 
         more points) does not equal xmin or xmax, respectively
      (3) a model block has a P-wave velocity less than or equal 
         to zero
      (4) a line  specifying the  model (x-  or z-coordinates or  
         upper or lower  velocity) or a  blank line  in the file  
         r.in or  v.in  has  been  omitted  (i.e.,  the file  is  
         incomplete)

*** array size error  for number of model  points *** - the  size 
   of the arrays specifying the maximum number of points defining 
   a layer boundary and/or the upper or lower  layer velocity is 
   not a multiple of 10

*** maximum number of  blocks in layer _  exceeded *** - a  layer 
   in the velocity model will  consist of more than  the maximum 
   number of trapezoids  allowed for  a single  layer given  the 
   current form  of  the  model.  Reduce the  number  of  points  
   defining the upper and/or lower boundary or  velocity for the 
   particular layer.

*** location of shot  point outside model ***  - a shot point  is 
    located outside the model.

*** error  in specification  of  amin or  amax  *** -  values  of 
   amin or amax have not been specified or are  greater than 180 
   in absolute value.

*** max  reflecting  boundaries  exceeded  *** -  the  number  of  
   reflecting boundaries in nrbnd  is greater than  that allowed 
   for one or more ray groups.

*** max  converting  boundaries  exceeded  *** -  the  number  of  
   converting boundaries in ncbnd  is greater than  that allowed 
   for one or more ray groups.

*** reflecting  boundary  greater  than  #  of  layers  ***  -  a  
   boundary in rbnd is  greater than or  equal to the  number of 
   model layers.

*** no  ray  codes  specified  ***  -  no  ray  codes  have  been  
   specified in the array ray.

*** shot# _  ray code  _ no  rays traced  *** -  the search  mode 
   was unable  to find  rays for  the  shot point  and ray  code 
   specified.

*** shot# _ ray  code _ 1  ray traced *** -  the search mode  was 
   unable to find the maximum take-off angle of  a refracted ray 
   group for the shot point and ray code specified; only a single 
   ray with  a take-off  angle  equal to  the  minimum value  is  
   traced.

*** less  than  nray rays  traced  for _  ray  groups ***  -  the 
   search mode was unable to find rays (or traced less than nray 
   rays) for the number of ray groups specified.

*** possible  inaccuracies  in  rngkta  ***  -  the  Runge  Kutta  
   routine has detected possible inaccuracies in  its attempt to 
   solve the ray tracing equations. The exact  point(s) at which 
   the problem  occurred can  be  found in  the  file r2.out  if  
   idump=1 is  used. The  problem  can be  eliminated by  either  
   reducing the velocity gradient in the appropriate location of 
   the model or reducing the value of step and/or smin.

*** ray stopped  - consists  of too many  points ***  - a ray  is 
   composed of  more than  the  maximum number  of points  (step  
   lengths) allowed. Tracing of this ray is terminated.

*** ray stopped  - intersected too  many boundaries ***  - a  ray 
   intersected more than the maximum number  of model boundaries 
   allowed. Tracing of this ray is terminated.

*** ray stopped -  illegal reflection ***  - a ray has  reflected 
   off a  boundary not  specified in  ray or  rbnd and  istop=1. 
   Tracing of this ray is terminated.

*** ray stopped - converted ray  cannot reflect/refract  *** -  a 
   ray is at a point of conversion from S to P and is beyond the 
   critical angle. Tracing of this ray is terminated.

***  ray  stopped  -  s-wave   cannot  propagate  ***  -  a   ray  
   propagating as an S-wave has  entered a model block  in which 
   the  S-wave  velocity  is  zero.  Tracing  of   this  ray  is  
   terminated.

*** ray  stopped -  reflected  from pinchout    *** -  the  layer 
   from which  a ray  is  to be  reflected  has zero  thickness.  
   Tracing of this ray is terminated.

*** ray  refl.  from  zero  vel.  contrast  boundary  ***  -  the  
   amplitude of a  ray reflected from  a zero  velocity contrast 
   boundary has been set to zero. If ampsmt>0,  the amplitude of 
   this ray may become greater than zero after smoothing.

*** ray attenuated  to zero amplitude  *** - the  amplitude of  a 
   ray is zero because of large Q attenuation.  If ampsmt>0, the 
   amplitude of  this ray  may  become greater  than zero  after  
   smoothing.

*** block  undetermined ***  -  this is  the most  serious  error 
    since it implies  that TRAMP  has lost  track of  what model  
    block a ray is supposed to be in and therefore implies there 
    is probably a bug in the code. The problem may be avoided if 
    the ray  step  length  is  reduced.  Also  check that  layer  
    boundaries do  not  cross  or  that  a  deeper  boundary  is  
    specified before a  shallower boundary  in the  file r.in or  
    v.in.