# The Hazard Library
# Copyright (C) 2012-2021 GEM Foundation
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
Module :mod:`openquake.hazardlib.source.area` defines :class:`AreaSource`.
"""
import math
from copy import deepcopy
from openquake.hazardlib import geo, mfd
from openquake.hazardlib.source.point import PointSource
from openquake.hazardlib.source.base import ParametricSeismicSource
from openquake.hazardlib.source.rupture import ParametricProbabilisticRupture
[docs]class AreaSource(ParametricSeismicSource):
"""
Area source represents uniform seismicity occurring over a geographical
region.
:param polygon:
An instance of :class:`openquake.hazardlib.geo.polygon.Polygon`
that defines source's area.
:param area_discretization:
Float number, polygon area discretization spacing in kilometers.
See :meth:`openquake.hazardlib.source.area.AreaSource.iter_ruptures`.
Other parameters (except ``location``) are the same as for
:class:`~openquake.hazardlib.source.point.PointSource`.
"""
code = b'A'
MODIFICATIONS = set()
def __init__(self, source_id, name, tectonic_region_type,
mfd, rupture_mesh_spacing,
magnitude_scaling_relationship, rupture_aspect_ratio,
temporal_occurrence_model,
# point-specific parameters (excluding location)
upper_seismogenic_depth, lower_seismogenic_depth,
nodal_plane_distribution, hypocenter_distribution,
# area-specific parameters
polygon, area_discretization):
super().__init__(
source_id, name, tectonic_region_type, mfd, rupture_mesh_spacing,
magnitude_scaling_relationship, rupture_aspect_ratio,
temporal_occurrence_model)
self.upper_seismogenic_depth = upper_seismogenic_depth
self.lower_seismogenic_depth = lower_seismogenic_depth
self.nodal_plane_distribution = nodal_plane_distribution
self.hypocenter_distribution = hypocenter_distribution
self.polygon = polygon
self.area_discretization = area_discretization
self.max_radius = 0
[docs] def iter_ruptures(self, **kwargs):
"""
See :meth:
`openquake.hazardlib.source.base.BaseSeismicSource.iter_ruptures`
for description of parameters and return value.
Area sources are treated as a collection of point sources
(see :mod:`openquake.hazardlib.source.point`) with uniform parameters.
Ruptures of area source are just a union of ruptures
of those point sources. The actual positions of the implied
point sources form a uniformly spaced mesh on the polygon.
Polygon's method :meth:
`~openquake.hazardlib.geo.polygon.Polygon.discretize`
is used for creating a mesh of points on the source's area.
Constructor's parameter ``area_discretization`` is used as
polygon's discretization spacing (not to be confused with
rupture surface's mesh spacing which is as well provided
to the constructor).
The ruptures' occurrence rates are rescaled with respect to number
of points the polygon discretizes to.
"""
polygon_mesh = self.polygon.discretize(self.area_discretization)
scaling_rate_factor = 1. / len(polygon_mesh)
# take the very first point of the polygon mesh
[epicenter0] = polygon_mesh[0:1]
# generate "reference ruptures" -- all the ruptures that have the same
# epicenter location (first point of the polygon's mesh) but different
# magnitudes, nodal planes, hypocenters' depths and occurrence rates
# NB: all this mumbo-jumbo is done to avoid multiple calls to
# PointSource._get_rupture_surface
ref_ruptures = []
for mag, mag_occ_rate in self.get_annual_occurrence_rates():
for np_prob, np in self.nodal_plane_distribution.data:
for hc_prob, hc_depth in self.hypocenter_distribution.data:
hypocenter = geo.Point(latitude=epicenter0.latitude,
longitude=epicenter0.longitude,
depth=hc_depth)
occurrence_rate = (mag_occ_rate * np_prob * hc_prob
* scaling_rate_factor)
surface, nhc = PointSource._get_rupture_surface(
self, mag, np, hypocenter)
if kwargs.get('shift_hypo'):
hc_depth = nhc.depth
ref_ruptures.append((mag, np.rake, hc_depth,
surface, occurrence_rate))
# for each of the epicenter positions generate as many ruptures
# as we generated "reference" ones: new ruptures differ only
# in hypocenter and surface location
for epicenter in polygon_mesh:
for mag, rake, hc_depth, surface, occ_rate in ref_ruptures:
# translate the surface from first epicenter position
# to the target one preserving it's geometry
surface = surface.translate(epicenter0, epicenter)
hypocenter = deepcopy(epicenter)
hypocenter.depth = hc_depth
rupture = ParametricProbabilisticRupture(
mag, rake, self.tectonic_region_type, hypocenter,
surface, occ_rate, self.temporal_occurrence_model)
yield rupture
[docs] def count_ruptures(self):
"""
See
:meth:`openquake.hazardlib.source.base.BaseSeismicSource.count_ruptures`
for description of parameters and return value.
"""
polygon_mesh = self.polygon.discretize(self.area_discretization)
return (len(polygon_mesh) *
len(self.get_annual_occurrence_rates()) *
len(self.nodal_plane_distribution.data) *
len(self.hypocenter_distribution.data))
def __iter__(self):
"""
Split an area source into a generator of point sources.
MFDs will be rescaled appropriately for the number of points in the
area mesh.
"""
mesh = self.polygon.discretize(self.area_discretization)
num_points = len(mesh)
area_mfd = self.mfd
if isinstance(area_mfd, mfd.TruncatedGRMFD):
new_mfd = mfd.TruncatedGRMFD(
a_val=area_mfd.a_val - math.log10(num_points),
b_val=area_mfd.b_val,
bin_width=area_mfd.bin_width,
min_mag=area_mfd.min_mag,
max_mag=area_mfd.max_mag)
elif isinstance(area_mfd, mfd.EvenlyDiscretizedMFD):
new_occur_rates = [x/num_points for x in area_mfd.occurrence_rates]
new_mfd = mfd.EvenlyDiscretizedMFD(
min_mag=area_mfd.min_mag,
bin_width=area_mfd.bin_width,
occurrence_rates=new_occur_rates)
elif isinstance(area_mfd, mfd.ArbitraryMFD):
new_occur_rates = [x/num_points for x in area_mfd.occurrence_rates]
new_mfd = mfd.ArbitraryMFD(
magnitudes=area_mfd.magnitudes,
occurrence_rates=new_occur_rates)
elif isinstance(area_mfd, mfd.YoungsCoppersmith1985MFD):
new_mfd = mfd.YoungsCoppersmith1985MFD.from_characteristic_rate(
area_mfd.min_mag, area_mfd.b_val, area_mfd.char_mag,
area_mfd.char_rate / num_points, area_mfd.bin_width)
else:
raise TypeError('Unknown MFD: %s' % area_mfd)
for i, (lon, lat) in enumerate(zip(mesh.lons, mesh.lats)):
pt = PointSource(
# Generate a new ID and name
source_id='%s:%s' % (self.source_id, i),
name=self.name,
tectonic_region_type=self.tectonic_region_type,
mfd=new_mfd,
rupture_mesh_spacing=self.rupture_mesh_spacing,
magnitude_scaling_relationship=
self.magnitude_scaling_relationship,
rupture_aspect_ratio=self.rupture_aspect_ratio,
upper_seismogenic_depth=self.upper_seismogenic_depth,
lower_seismogenic_depth=self.lower_seismogenic_depth,
location=geo.Point(lon, lat),
nodal_plane_distribution=self.nodal_plane_distribution,
hypocenter_distribution=self.hypocenter_distribution,
temporal_occurrence_model=self.temporal_occurrence_model)
pt.num_ruptures = pt.count_ruptures()
yield pt
[docs] def wkt(self):
"""
:returns: the geometry as a WKT string
"""
return self.polygon.wkt