Block V: Sources

OASP supports the same sources as SAFARI-FIPP, i.e explosive sources in fluids or solids or vertical point forces in solids (option X). Multible sources in a vertical array are supported. If sources with horizontal directionality are desired, the 3-dimensional version OASP3D must be used.

Source Types  

As in SAFARI the default source type in OASP is an explosive type compressional source. In addition to the optional vertical and horizontal point forces, various seismic moment sources have been added to OASP. The source type is specified by a number (1-5) in the option field (line 2). The translation is as follows:

1.

Explosive source (default) normalized to unit pressure at 1 m distance.

2.

Vertical point force with amplitude 1 N.

3.

Horizontal (in-plane) point force with amplitude 1 N.

4.

Dip-slip source with seismic moment 1 Nm. Dip angle specified in degrees in block V, following the other parameters.

5.

Omnidirectional seismic moment source representing explosive source. Same as type 1, but all three force dipoles have seismic moment 1 Nm.

Source Normalization

In SAFARI-FIPP, the source pulse shape was defined as the pressure pulse produced at a distance of 1 m from the source (for solids the negative of the normal stress 1 m below the source).

In OASP, the same source normalization has been maintained for point sources (explosive sources) in fluid media. For solid media, however, the sources are normalized to unit volume (1 m³) injection for explosive sources and unit force 1 N for point sources or 1 N/m for line sources.

User defined Source Arrays  

Version 1.6 of OASP has been upgraded to allow a user-defined source array through options l and v.

Option l is intended for general physical arrays with uneven spacing or special shadings, As for the built-in arrays, such user-defined arrays may be present in fluid as well as elastic media. The source type is specified as described above, and the array geometry and shading should be given in the file input.src in the following format

LS
SDC(1)  SDELAY(1)  SSTREN(1)    # Depth (m), Delay (s), Amplitude
SDC(2)  SDELAY(2)  SSTREN(2) 
SDC(3)  SDELAY(3)  SSTREN(3) 
  :        :          :
  :        :          :
SDC(LS) SDELAY(LS) SSTREN(LS)

Option v is more general in the sense that it allows for different source types to be mixed in the array, and the pure time delay is replaced by a specification of the complex amplitudes in the frequency domain, allowing for representation of multibles etc. This option is used for virtual arrays such as those imposed by coupling of wave systems. For example, this option is used for coupling tube wave phenomenae to propagation in a stratified formation when modeling borehole seismics. Option v is only allowed for source arrays in elastic media (including transversily isotropic layers). The complex amplitudes of the source array is specified in the file input.strf. This should be an ASCII trf file, and the frequency sampling should be consistent with the frequency sampling selected in the input file input.dat. There are 3 source types available. All are omnidirectional in the horizontal. The source type is identified by a type number in the file header, and each depth can have one of each source type present. The possible source types are:

10

Seismic monopole, i.e. 3 perpendicular and identical force dipoles. The unit is seismic moment (Nm).

11

Vertical force dipole. The unit is seismic moment (Nm).

12

Vertical force, positive downwards. The unit is force (N).

The source types are regognized by PP which can therefore be used to check your source timeseries by simply specifying input.strf in Field 1 of the PP main menu. An example of an strf-file for 21 source depths, with a monopole and a dipole source at each depth, is

 PULSETRF                               # TRF file identification
 OASP16                                 # Calculating program
           2                            # No. sources per depth NSIN
          10          11                # Source types
 tube wave simulation                   # Title
 +                                      # Sign if time factor exponent
 400.0                                  # Center frequency 
   6.0                                  # Depth of primary source
  -0.5  19.5  21                        # SD-min, SD-max, LS
   0.0   0.0   1                        # Range (fixed).
  1024   2   104  0.0001                # Time/frequency parameters
           1                            # Dummy
  -38.20335                             # Imag. part of frequencies
           1                            # One Fourier order (fixed)
           1                            # Fixed
           0                            # Dummy
           0                            # Dummy
           0                            # Dummy
  0.0                                   # Dummy
  0.0                                   # Dummy
  0.0                                   # Dummy
  0.0                                   # Dummy
  0.0                                   # Dummy
  -24.15950 82.01517 -24.15950 82.01517 # Data
  -28.20251 83.04697 -28.20251 83.04697 # Data
  -32.38960 83.93490 -32.38960 83.93490 # Data
  -36.71837 84.66933 -36.71837 84.66933 # Data
  -41.18590 85.24049 -41.18590 85.24049 # Data
       :        :         :        :        :

Note: All lines should start with an empty space!. The time/frequency parameters are given in the form

 NT  LX  MX  DT

where

NT

is the number of time samples

DT

is the time sampling interval in seconds

LX

is the index of the first frequency, LX = INT(FR1*DT)

MX

is the index of the last frequency, MX = INT(FR2*DT)

The complex data must be written in the following loop structure

      DO 10 K = LX,MX
       DO 10 L = 1,LS
        WRITE(15,*) (REAL(TRF(K,L,M)),AIMAG(TRF(K,L,M)), M=1,NSIN)
 10   CONTINUE