tramp.doc

实现地震射线追踪和反演的frotran程序

   of the Lth layer
   (4) L.0  - ray  take-off angles  supplied by  the user  in the  
   arrays amin and amax

nray - an  array containing the  number of rays  to be  traced for 
   each ray group  in the  array ray  (default: 10;  however, the  
   default is the first element of nray for all ray groups if only 
   one value is specified)

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 in which 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)

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)

angbnd - maximum  allowable angular  difference (degrees)  between 
   the angle of the boundary along which head waves originate and 
   emerge (default: 20)

dbnd - an array  containing the layers  along the bottom  of which 
   diffracted waves are to be generated  if a downward travelling 
   ray  intersects  the   lower  layer  boundary;   each  element   
   corresponds to the ray groups in the array ray; the spacing of 
   emerging rays along the boundary is hws  (km) and the angle of 
   emergence equals the angle of incidence of the generating ray; 
   the velocity  of  propagation along  the  boundary equals  the  
   velocity directly beneath  the boundary; amplitudes  cannot be  
   calculated for this type of ray

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)

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

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 smoothing filter 
   to each layer boundary if ibsmth=1 or 2 (default: 10)

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) 
   (default: (xmax-xmin)/4500 and (xmax-xmin)/15)

4) Amplitude parameters (AMPPAR namelist):

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

iamp  -  calculate  ray  theoretical   amplitudes  if  iamp=1  or  
   calculate amplitudes  and plot  amplitude-distance  curves if  
   iamp=2 (default: 0)

isect - calculate the  time, amplitude and phase  of each arrival  
   of the  synthetic  sections by  interpolating  the  calculated 
   travel time- and amplitude-distance curves and write these to  
   the file sect.out for input to the plotting program PLTSYN; the 
   seismogram locations are specified by xmins, xmaxs and xincs if 
   isect=1 or contained in the  file rec.in if isect=2 (default:  
   0)

ibreak - an array corresponding  to the ray groups  listed in the 
   array ray to split into prograde and retrograde segments when  
   (1) plotting travel time- and ampltude-distance curves (itx=1),
   (2) fitting cubic splines to the range versus take-off angle values 
   to evaluate the in-plane spreading,  and (3) interpolating to  
   obtain an arrival at  a seismogram location  if isect=1 or  2; 
   also to increment the integer code  by one in the file tx.out  
   when changing from a  prograde to retrograde  segment or vice  
   versa if itxout=1 (default: 1)

iint - an  array corresponding  to the  ray groups  listed in  the 
   array ray  to  use  all arrivals  in  a  particular ray  group  
   regardless or  their calculated  ray code  when (1)  fitting a  
   cubic spline  to the  range  versus take-off  angle  values to  
   determine the  in-plane spreading,  and  (2) interpolating  to  
   calculate the arrivals of the  synthetic sections; iint=0 will 
   ensure that  cubic  splines  will  involve  rays  of the  same  
   calculated ray code and  that interpolation will  be performed 
   across two successive arrivals of the  same ray code (default: 
   0)

icaust -  add a 90 degree phase  shift  to  a  retrograde  branch  of  
   refracted arrivals  (ray code  L.1) to  represent  the passage  
   through a single caustic (default: 1)

icomp - seismometer type: icomp=1 for  vertical component, icomp=0 
   for horizontal component (default: 1)

icmp - measure  the receiver  locations with  respect to the  shot 
   points (positive to the right, negative to the left) and output 
   the mid-point  and  half-offset  of  each  trace  to the  file  
   sect.out; icmp=0 will ensure that  the receivers are specified 
   with respect to model distance if iszero=0, or with respect to 
   the shot  points  and  the  directions  specified  by  idr  if  
   iszero=1 (default: 0)

iden - convert the  velocity model to constant-density  blocks and 
   output to  the  file  m.out for  use  as  input  to a  gravity  
   modelling program (default: 0)

surcon - calculate  the surface  conversion coefficient  (default: 
   1)

amprev - calculate the amplitudes of refracted  and reflected rays 
   in the reverse direction  to which they  were traced (default:  
   0)

b) Other amplitude parameters:

ampsmt - number of applications, N, of a  3-point smoothing filter 
   to amplitude curves is given by

                         N = ampsmt (n-2)

   where n is  the number of  arrivals in  the corresponding  
   cubic spline used  to determine  the in-plane  spreading for
   refracted and reflected ray groups, or the number of arrivals in
   the ray group for a head wave ray group; this smoothing can be 
   used  to remove some of  the artificial highs and lows often 
   associated with ray amplitudes (default: 0.1)

spamp -  ratio of  S-wave  to P-wave  displacement  at the  source  
   (default: 1)

denc -  an  array  containing  the  coefficients  of  a  4th-order  
   polynomial relating P-wave velocity, vp  (km/s), to density, r 
   (g/cm3), where
   
  r  = denc(1) + denc(2)vp + denc(3)vp2 + denc(4)vp3 + denc(5)vp4;
   
   if poisson's ratio equals  0.5, the material is  assumed to be 
   water and  r=1.0; this  relationship fits  empirical  data for  
   1<vp<9 (default: -.6997, 2.2302, -.598, .07036, -.0028311)
   
denmin  -  minimum  density  (g/cm3)  for   a  non-water  material  
   (default: 1.25)

ncaust - an array to  add a phase shift equal  to 90x(ncaust) degrees 
   to the ray groups in the array ray (default: 0)

omega  -  dominant  fequency   (Hz)  used  in  calculation   of  Q  
   attenuation and head wave amplitudes (default: 5)

hedcut -  the amplitude  of  all head  waves  that have  travelled  
   along the head wave boundary less than  Hmin (km) will have an 
   amplitude equal to that ray which travelled exactly Hmin along 
   the boundary where Hmin equals hedcut  percentage of the first 
   head wave  of the  group, i.e.,  the minimum-range  head wave;  
   hedcut is used to avoid an infinite  amplitude at the critical 
   point predicted by asymptotic ray theory (default: 25)

qp,  qs  -  arrays  containing   the  P-  and  S-wave   Q  values,  
   respectively, for each layer  of the velocity  model (default: 
   infinite, infinite; however, the default  is the first element 
   of qp (or qs) for all layers if only one value is specified)

ql,  qb  -  arrays  containing  the  layers   and  block  numbers,  
   respectively, of  model  trapezoids within  which  the P-  and  
   S-wave Q values are modified over that given by qp and qs using 
   the array qpbl first, followed by qsbl

qpbl, qsbl  -  arrays  containing  the  P- and  S-wave  Q  values,  
   respectively, for model trapezoids specified  by the arrays ql 
   and qb overriding the values assigned using  the arrays qp and 
   qs

xmins, xmaxs  -  minimum  and  maximum seismogram  location  (km),  
   respectively,  if   isect=1   (default:   xmin+(xmax-xmin)/50,   
   xmax-(xmax-xmin)/50)

xincs   -   seismogram   spacing   (km)   if   isect=1   (default:   
   (xmaxs-xmins)/48)

                         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 xmin).

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