Internal friction

Lal Vp (Anhydrite, Basalt, Chalk, Claystone, Coal, Dolomite, Halite, Limestone, Marl, Mudstone, Sandstone, Shale, Siltstone)

Chang & Zoback (Anhydrite, Basalt, Chalk, Claystone, Coal, Dolomite, Halite, Limestone, Marl, Mudstone, Sandstone, Shale, Siltstone)

18.532 in km/sec

Internal friction from GR (Anhydrite, Basalt, Chalk, Claystone, Coal, Dolomite, Halite, Limestone, Marl, Mudstone, Sandstone, Shale, Siltstone)

μ = tan(-24.17ln(GR)+139.68

-24.17 in 1/api

139.68 is a non-dimensional constant.

where GR is the gamma-ray log.