Source code for openquake.hazardlib.gsim.fukushima_tanaka_1990

# -*- coding: utf-8 -*-
# vim: tabstop=4 shiftwidth=4 softtabstop=4
#
# Copyright (C) 2014-2023 GEM Foundation
#
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"""
Module exports :class:'FukushimaTanaka1990' and :class:
'FukushimaTanakaSite1990'
"""
import numpy as np
from scipy.constants import g


from openquake.hazardlib.gsim.base import GMPE, CoeffsTable
from openquake.hazardlib import const
from openquake.hazardlib.imt import PGA


def _compute_distance_scaling(C, rrup, mag):
    """
    Returns the distance scaling term
    """
    rscale1 = rrup + C["c2"] * (10.0 ** (C["c3"] * mag))
    return -np.log10(rscale1) - (C["c4"] * rrup)


def _compute_magnitude_scaling(C, mag):
    """
    Returns the magnitude scaling term
    """
    return C["c1"] * mag + C["c5"]


def _compute_site_scaling(vs30, mean):
    """
    Scales the ground motions by increasing 40 % on NEHRP class D/E sites,
    and decreasing by 40 % on NEHRP class A/B sites
    """
    site_factor = np.ones(len(vs30), dtype=float)
    idx = vs30 <= 360.
    site_factor[idx] = 1.4
    idx = vs30 > 760.0
    site_factor[idx] = 0.6
    return np.log(np.exp(mean) * site_factor)


class FukushimaTanaka1990(GMPE):
    """
    Implements the PGA GMPE of Fukushima and Tanaka (1990)
    Fukushima, Y. and Tanaka, T. (1990) A New Attenuation Relation for Peak
    Horizontal Acceleration of Strong Earthquake Ground Motion in Japan.
    Bulletin of the Seismological Society of America, 80(4), 757 - 783
    """
    #: The GMPE is derived from shallow earthquakes in California and Japan
    DEFINED_FOR_TECTONIC_REGION_TYPE = const.TRT.ACTIVE_SHALLOW_CRUST

    #: Supported intensity measure types are peak ground acceleration
    DEFINED_FOR_INTENSITY_MEASURE_TYPES = {PGA}

    #: Supported intensity measure component is the average horizontal
    #: component
    #: :attr:`openquake.hazardlib.const.IMC.GEOMETRIC_MEAN`,
    DEFINED_FOR_INTENSITY_MEASURE_COMPONENT = const.IMC.GEOMETRIC_MEAN

    #: Supported standard deviation types is total.
    DEFINED_FOR_STANDARD_DEVIATION_TYPES = {const.StdDev.TOTAL}

    #: Required site parameters. The GMPE was developed for an ''average''
    #: site conditions. The authors specify that for rock sites the
    #: values should be lowered by 40 % and for soil site they should be
    #: raised by 40 %. For greatest consistencty the site condition is
    #: neglected currently but a site-dependent GMPE may be implemented
    #: inside a subclass.
    REQUIRES_SITES_PARAMETERS = set()

    #: Required rupture parameters are magnitude
    REQUIRES_RUPTURE_PARAMETERS = {'mag'}

    #: Required distance measure is rupture distance
    REQUIRES_DISTANCES = {'rrup'}

    def compute(self, ctx: np.recarray, imts, mean, sig, tau, phi):
        """
        See :meth:`superclass method
        <.base.GroundShakingIntensityModel.compute>`
        for spec of input and result values.
        """
        for m, imt in enumerate(imts):
            C = self.COEFFS[imt]

            imean = (_compute_magnitude_scaling(C, ctx.mag) +
                     _compute_distance_scaling(C, ctx.rrup, ctx.mag))
            # Original GMPE returns log10 acceleration in cm/s/s
            # Converts to natural logarithm of g
            mean[m] = np.log((10.0 ** (imean - 2.0)) / g)
            if self.REQUIRES_SITES_PARAMETERS:  # in subclass
                mean[m] = _compute_site_scaling(ctx.vs30, mean[m])

            # Convert from common logarithm to natural logarithm
            sig[m] = np.log(10 ** C['sigma'])

    COEFFS = CoeffsTable(sa_damping=5, table="""
    IMT     c1      c2     c3         c4    c5   sigma
    pga   0.41   0.032   0.41    0.0034  1.30    0.21
    """)


class FukushimaTanakaSite1990(FukushimaTanaka1990):
    """
    Implements the Fukushima and Tanaka (1990) model correcting for
    site class. The authors specify that the ground motions should
    be raised by 40 % on soft soil sites and reduced by 40 % on rock sites.
    The specific site classification is not known, so it is assumed that
    in this context "average" site conditions refer to NEHRP C, rock conditions
    to NEHRP A and B, and soft soil conditions to NEHRP D and E
    """
    #: Input sites as vs30 although only three classes considered
    REQUIRES_SITES_PARAMETERS = {"vs30"}