Implements the Douglas et al. (2013) GMPE (Stochastic)

Implements the Douglas et al (2013) GMPE to characterise ground motion from induced seismicity in geothermal regions, as derived using stochastic simulations of ground motions. The GMPE itself is a collection of 36 GMPEs, of the same functional form, with coefficients given for different combinations of stress drop (1, 10, 100 bar), attenuation quality factor Q (200, 600, 1800) and kappa (0.005, 0.02, 0.04, 0.06 s). These modelling parameters are intended to be treated as epistemic uncertainties (see Douglas and Edwards, 2013); hence, all GMPEs are implemented separately here.

Douglas et al (2013) also provide coefficients for an empirical GMPE, which will be implemented in due course.

1) Adds "GEOTHERMAL" to the const.py class
2) Implements Douglas et al (2013) stochastic GMPE
3) Tests all 36 different GMPEs against a Fortran implementation supplied by J. Douglas

More explanation is supplied in the doc string of the initial implementation class.