Dispersive Media

For pulse problems where causality is critical, non-zero attenuation must be accompanied by frequency-dependent wave speeds. Since this is of main importance for seismic problems with relatively high attenuation, the specification of dispersive wave speeds has been limited to elastic media only. A dispersive layer is again flagged by a negative value of c_c:

c_c=-3:

A dispersive layer is specified as followsin the file input.dat:

D	-3	0	0	0			[L]
LTYP

The only significant parameters for the layer are the depth D, the density and the roughness parameters and L. The parameter LTYP is a type-identifier for the layer. The frequency dependence of the wave speeds and attenuations should be specified in the file input.dis, which may contain several dispersion laws. The file should contain a block of data in the form of a frequency table, for each value of LTYP specified in input.dat, with the first block corresponding to LTYP = 1, the second corresponding to LTYP = 2 etc. The format for each block is asfollows:

NF                                         # Number of freqs.
F(1)    CC(1)    CS(1)    AC(1)    AS(1)   # Freq, speeds, atten.
F(2)    CC(2)    CS(2)    AC(2)    AS(2)   # Freq, speeds, atten.
 :        :        :        :        :
F(N)    CC(N)    CS(N)    AC(N)    AS(N)   # Freq, speeds, atten.

The table does not have to be equidistant. OASES will interpolate to create a table consistent with the frequency sampling specified in input.dat.