COD wave parameter calculation using Center of damage utility module

Hi friends,

SACS use the following values in “Center of Damage Utility Version 11.2.0.15” for calculating COD wave parameter.

“For foundation linearization;

In the exponent am, the term a is taken as 1.8 and m is the inverse slope of
the S-N curve. The effective wave height Heff and associated period Teff are
taken as:

Heff = 0.89 * Hcs Teff = 0.84 * Tcz

For most probable maximum wave;

The exponent term am is taken as 3.0 and the most probable maximum wave height
Href and the associated period Tref are taken as:

Href = 1.86 * Hcs Tref = Tcz / 0.81”

Can anyone give the reference for these values? Or

How to arrive this value ?