{"id":304,"date":"2012-10-03T09:04:33","date_gmt":"2012-10-03T09:04:33","guid":{"rendered":"http:\/\/ahay.org\/blog\/?p=304"},"modified":"2015-09-02T17:03:41","modified_gmt":"2015-09-02T17:03:41","slug":"program-of-the-month-sfkirmod","status":"publish","type":"post","link":"https:\/\/ahay.org\/blog\/2012\/10\/03\/program-of-the-month-sfkirmod\/","title":{"rendered":"Program of the month: sfkirmod"},"content":{"rendered":"

sfkirmod<\/a> is a program for modeling seismic reflection data using the Kirchhoff method. According to this method, the reflection response is computed by integrating over the reflector surface. For a theoretical derivation, see, for example,<\/p>\n

Haddon, R. A. W., and P. W. Buchen, 1981, Use of Kirchhoff’s formula for body wave calculations in the earth: Geophys. J. Roy. Astr. Soc., 67, 587-598. <\/p>\n

At the moment, sfkirmod can handle only asymptotic Green’s functions, analytically computed in three kinds of velocity models: <\/p>\n

    \n
  1. Constant velocity<\/li>\n
  2. Constant gradient of velocity<\/li>\n
  3. Constant gradient of velocity squared<\/li>\n<\/ol>\n

    The type is specified with type=<\/strong> parameter, and the velocity model is specified with vel=<\/strong>, refx=<\/strong>, refz=<\/strong>, gradx=<\/strong>, and gradz=<\/strong>. <\/p>\n

    The following example from rsf\/scons\/rsf<\/a> shows shot gathers modeled by sfkirmod<\/strong> in a medium with horizontal reflectors and a constant vertical gradient of velocity <\/p>\n

    \"\" <\/p>\n

    It is also possible to model a converted (PS or SP) wave by supplying vel2=<\/strong>, gradx2=<\/strong>, and gradz2=<\/strong> to specify the converted velocity. The standard input file for sfkirmod<\/strong> contains the shape of one or more reflectors. Several other input files can be optionally provided: dip=<\/strong> specifies the slope of the reflector(s), refl=<\/strong> specifies normal-incidence reflectivity (AVA intercept), rgrad=<\/strong> specifies AVA gradient. <\/p>\n

    The sampling of the time axis in the output is controlled by nt=<\/strong>, t0=<\/strong>, and dt=<\/strong> parameters. A Ricker wavelet is used with the peak frequency specified by freq=<\/strong>. Factors such as the geometrical spreading and the obliquity factor are taken into account. The geometrical spreading correction is different for 2-D (cylindrical waves) or 2.5-D (spherical waves). The default behavior is 2.5_D. To switch to 2-D, use twod=y<\/strong>. By default, sfkirmod<\/strong> outputs shot gathers. <\/p>\n

    It is also possible to compute CMP gathers directly by using cmp=y<\/strong>. The following example from jsg\/crs\/dome2<\/a> shows CMP gathers computed over a hyperbolic-shape reflector. <\/p>\n

    \"\" <\/p>\n

    Since Kirchhoff modeling is fundamentally a linear operation, it is easy to run sfkirmod<\/strong> in a data-parallel fashion, for example by using pscons<\/a> with split=[1,n1]<\/strong> and reduce=’add’<\/strong>. <\/p>\n

    The 3-D version of sfkirmod<\/strong> is sfkirmod3<\/a>. <\/p>\n

    10 previous programs of the month<\/h3>\n