rayinvr.doc

实现地震射线追踪和反演的frotran程序

space - an array which  determines the spacing of  take-off angles 
   between the minimum and  maximum values for each  ray group in 
   the array  ray.  For  space=1,  the  take-off  angles will  be  
   equally spaced;  for  space>1,  the  take-off angles  will  be  
   concentrated  near  the  minimum  value;  for  0<space<1,  the  
   take-off angles will  be concentrated  near the  maximum value  
   (default: 1;  however, space=2  for a  reflected ray  group if  
   specified as L.2 in the array ray)

amin, amax  -  arrays  containing  minimum  and  maximum  take-off  
   angles  (degrees);  measured  from  the  horizontal,  positive  
   downward and negative upward (for rays traveling left to right 
   or right to left); used for ray groups specified by ray=1.0

nsmax -  an array  containing the  maximum number  of rays  traced 
   when searching for the take-off angles of the ray groups in the 
   array ray  (default: 10;  however,  the default  is  the first  
   element of  nsmax for  all  ray groups  if only  one  value is  
   specified)

n2pt - maximum number of iterations during two-point ray tracing
   (i2pt>0); this is the maximum number of rays traced for each
   receiver to determine the take-off angle of the ray that
   connects the source and receiver (default: 5)

x2pt - distance tolerance (km) for two-point ray tracing; less than
   n2pt rays will be traced for a particular receiver if a ray end 
   point is within x2pt of the receiver location 
   (default: (xmax-xmin)/2000)

crit - head waves are generated if a down-going  ray in the search 
   mode has an angle of incidence at the  bottom of the Lth layer 
   within  crit  degrees  of  the  critical  angle  when  ray=L.3  
   (default: 1)

hws - the spacing (km) of rays emerging upward  from the bottom of 
   the Lth layer when ray=L.3 (default: (xmax-xmin)/25)

nhray - maximum number of rays traced for a head wave ray group
   (default: pnrayf)

aamin - minimum  take-off angle  (degrees) for  the refracted  ray 
   group in the first layer (default: 5)

aamax - maximum take-off angle (degrees) for  reflected ray groups 
   specified as L.2 in the array ray (default: 85)

stol - if a ray traced in  the search mode is of the  correct type 
   and its  end point  is within  stol (km)  of the  previous ray  
   traced in the search mode, then the search for that ray type is 
   terminated; a value of stol=0 will ensure  that nsmax rays are 
   always traced in the search mode (default: (xmax-xmin)/3500)

xsmax - for  reflected ray  groups specified as  L.2 in  the array 
   ray, determine the minimum take-off angle using the search mode 
   so that the maximum range for this ray  group is xsmax (km) if 
   iturn=0 or  the  maximum offset  of  the  reflection point  is  
   xsmax/2 (km) if iturn=1; for head wave ray groups specified as 
   L.3 in  the array  ray,  the maximum  offset of  the  point of  
   emergence from the head wave  boundary is xsmax  (km); xsmax=0  
   will ensure that the take-off angle of the reflected ray which 
   grazes off the bottom of the Lth  layer is determined and head 
   waves are traced along the Lth boundary  until the edge of the 
   model is reached (default: 0.0)

nrbnd - an  array containing the  number of  reflecting boundaries 
   for each ray group in the array ray (default: 0)

rbnd - an array containing the reflecting  boundaries specified in 
   the array nrbnd; the following code is used:
   (1) L -  ray traveling  downward is  reflected upward  off the  
   bottom of the Lth layer
   (2) -L -  ray traveling upward  is reflected downward  off the  
   top of the Lth layer

ncbnd - an array containing the number of converting (P  to S or S 
   to P) boundaries for each ray group in the array ray (default: 
   0)

cbnd - an array containing the converting  boundaries specified in 
   the array ncbnd; the following code is used:
   (1) i   - ray will  convert from its  present wave type  (P or  
   S) at the ith layer boundary encountered
   (2) 0 - ray will leave the source as an S-wave

frbnd - an  array containing the  floating reflecting boundaries 
   for each ray group in the array ray; the values of frbnd 
   correspond to the order in which the reflectors are listed in
   the file f.in  (default: 0)

pois - an array containing  the value of Poisson's ratio  for each 
   model layer; a  value of  0.5 signifies  a water layer  with a  
   corresponding  S-wave   velocity  of   zero   (default:  0.25;   
   however, the  default is  the first  element of  pois  for all  
   layers if only one value is specified)

poisl, poisb -  arrays specifying  the layers  and block  numbers, 
   respectively, of model trapezoids within which Poisson's ratio 
   is modified over that given by pois using the array poisbl; for 
   poisb, the trapezoids with  a layer are numbered  from left to 
   right

poisbl - an array containing the value of Poisson's  ratio for the 
   model trapezoids  specified  in  the  arrays poisl  and  poisb  
   overriding the values assigned using the array pois

npbnd  -  number  of  points  at  which  each  layer  boundary  is  
   uniformly sampled  for smoothing  if ibsmth=1  or  2 (default:  
   100)

nbsmth - number of applications of a  three-point averaging filter 
   to each layer boundary if ibsmth=1 or 2 (default: 10)

xminns, xmaxns - minimum and maximum model distance over which the
   layer boundaries listed in the array insmth are not to be smoothed
   using ibsmth=1 or 2 (defaults: smooth boundaries between xmin and 
   xmax) 

step - controls  the ray step  length in the  solution of  the ray 
   tracing equations according to the relationship

             step length (km) = step*v/(|vx|+|vz|) 

  where   v   is  velocity   and   vx   and  vz   are   its   partial  
   derivatives with respect to x and z (default: 0.05)

smin, smax -  minimum and maximum  allowable ray step  length (km) 
   (defaults: (xmax-xmin)/4500, (xmax-xmin)/15)

4) Inversion parameters (INVPAR namelist):

a) Switches  (usually 0 = off, 1 = on):

invr -  calculate  partial  derivatives  of  the  selected  model  
   parameters and write these to the file i.out (default: 0)

b) Other inversion parameters:

ivray - an  array of  non-zero integers  corresponding to the  ray 
   groups listed in the  array ray used  to identify the  type of 
   arrival in the file tx.out if itxout=2 or 3 and to allow for the 
   appropriate comparison with the  observed travel times  in the 
   file tx.in if invr=1 or i2pt>0

ximax - the maximum allowable distance (km) between the nearest ray
   end point and an observed seismogram location for one of the rays
   used to interpolate the partial derivatives and travel time at
   that observed seismogram location (default: (xmax-xmin)/20)

ttunc - uncertainty of the calculated travel times  (s) written to 
   the file tx.out if itxout>0 (default: 0.01)

bndunc, velunc -  estimated uncertainty of  the depth  of boundary 
   nodes (km)  and velocities  (km/s) written  to the  file i.out  
   (defaults: 0.1, 0.1)

                         Additional Notes

Array defaults: if  a single  default value is  indicated for  an 
   array parameter, all elements of the array  have that default 
   value.

Layer boundaries: must begin at xmin and end at xmax even  if the 
   layer above and/or below is pinched out  (unless the boundary 
   is defined by only one point, then it is specified at xmax).

Bottom layer boundary: should consist of at most ten points.

Near-vertical layer boundaries:  should be  avoided because  they 
   may result in large velocity gradients  nearby. If necessary, 
   the adjacent trapezoids should have zero velocity gradient.

Shot point locations: may be anywhere in the model,  but locating 
   them directly on a model boundary may cause problems.

Ray group: is defined as a set of rays specified by a ray code in 
   the  array  ray,   possibly  modified  to   include  multiple  
   reflections and/or  conversions,  whose take-off  angles  are  
   determined by an  iterative search mode  or specified  by the 
   user using ray=1.0 and the arrays amin and amax.

Zero velocity gradient: if the four corner velocities of  a model 
   trapezoid are equal, then  there is a zero  velocity gradient 
   inside and no  ray bending  will occur.  It is preferable  to 
   have a zero gradient in all or part of a  layer rather than a 
   very small gradient  so that the  Runge Kutta routine  can be 
   avoided and straight ray paths are used.

Large velocity gradients: ray  tracing becomes inaccurate if  the 
   velocity gradient is  large and  the ray  step length is  not 
   small enough. In this case a warning message is given and the 
   value of smin and/or step should be reduced.

Ray code:  listed in  the  file r1.out  for  each ray  traced  is 
   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 travelled 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 particular 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 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. 
   This may  be  undesirable  if  the  prograde  and  retrograde  
   branches should be identified by a single number for inversion 
   or if more than one ray group should be identified by the same 
   number, in which case itxout=2 or 3 and the array  ivray should 
   be used when writing to the file tx.out.

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 
   xmax. 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  xmax and 
   assign a lower layer velocity of zero at xmax.

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 xmax.

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

Fixed  vertical  velocity  gradient:  if  the  vertical  velocity