Block V: Sources

OAST supports the same sources as SAFARI-FIP, 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. The significance of the source parameters are as follows

SD:

Source depth in m. If option 'L' has been specified, then SD defines the mid-point of the vertical source array.

NS:

Number of sources in the array.

DS:

Source spacing in m.

AN:

Specifies the nominal grazing ANG of the generated beam in degrees. ANG>0 corresponds to downward propagation.

IA:

Array type

1.

Rectangular weighted array

2.

Hanning weighted array

3.

Hanning weighted focusing array

4.

Gaussian weighted array

5.

Gaussian weighted focusing array

FD:

Focal depth in m for an array of type 3 and 5.

DA:

Dip angle in degrees for dip-slip sources (type 4).

Source Types  

As in SAFARI the default source type in OAST is an explosive type compressional source. In addition to the optional vertical point force, and axisymmetric seismic moment source has been added to OAST. The source type is specified by a number (1-3) 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, the source strength was normalized to yield unit pressure (in Pa) at a distance of 1 m from the source (for solids the negative of the normal stress 1 m below the source).

In OASES, 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 OAST has been upgraded to allow a user-defined source array through option l.

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 array definition 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)