Update NRML Schema for seismic source model

[Damiano Monelli]

[et=16h]
[at=9h]

The NRML schema for the seismic source model (https://github.com/gem/nrml/blob/master/schema/hazard/source_model.xsd#L24) needs to be updated to be compatible with the source data model developed in NHLIB.

As in the current schema, 4 source typologies have to be defined:
- Point Source
- Area Source
- Simple Fault Source
- Complex Fault Source

----------
Each source typology is defined by the following common parameters:

- source_id:
        Some (numeric or literal) source identifier. Supposed to be unique within the source model.

- name:
        String, a human-readable name of the source.

- tectonic_region_type:
        String representing source's tectonic regime. Represents one of the constants defined in `nhlib.const.TRT`.

- mfd:
        Magnitude-Frequency distribution for the source. Represents one of the mfds defined in `nhlib.mfd`, that is EvenlyDiscretizedMFD, and TruncatedGRMFD.
For the TruncatedGRMFD the schema should represent all the parameters required in the NHLIB object definition except the bin_width.

- magnitude_scaling_relationship:
        String identifying one of the magnitude scaling relationship defined in `nhlib.msr.base.BaseMSR`, that is 'PeerMSR' and 'WC1994'

- rupture_aspect_ratio:
        Float number representing how much source's ruptures are more wide
        than tall. It must be greater than zero.

----------
The Point Source is defined by the following additional parameters:

- upper_seismogenic_depth:
        Float number, must be greater or equal than zero. Represents minimum depth an earthquake rupture can reach, in km.

- lower_seismogenic_depth:
        Float number, must be greater or equal than zero. Represents maximum depth an earthquake rupture can reach, in km.

- location:
     Point geographical location, defined by longitude and latitude

- nodal_plane_distribution:
        represents `nhlib.pmf.PMF` object with values that are instances of `nhlib.source.nodalplane.NodalPlane`. Shows the distribution of probability for rupture to have the certain nodal plane.

- hypocenter_distribution:
        represents `nhlib.pmf.PMF` with values being float numbers in km
        representing the depth of the hypocenter.

----------
The Area Source is defined by the following additional parameters:

- upper_seismogenic_depth:
        Float number, must be greater or equal than zero. Represents minimum depth an earthquake rupture can reach, in km.

- lower_seismogenic_depth:
        Float number, must be greater or equal than zero. Represents maximum depth an earthquake rupture can reach, in km.

- area_boundary:
        2D polygon (each vertex defined by longitude, latitude) defining area boundary.

- nodal_plane_distribution:
        represents `nhlib.pmf.PMF` object with values that are instances of `nhlib.source.nodalplane.NodalPlane`. Shows the distribution of probability for rupture to have the certain nodal plane.

- hypocenter_distribution:
        represents `nhlib.pmf.PMF` with values being float numbers in km
        representing the depth of the hypocenter.

----------
The Simple Fault Source is defined by the following additional parameters:

- upper_seismogenic_depth:
        Float number, must be greater or equal than zero. Represents minimum depth an earthquake rupture can reach, in km.

- lower_seismogenic_depth:
        Float number, must be greater or equal than zero. Represents maximum depth an earthquake rupture can reach, in km.

- fault_trace:
        2D line (each point in the line represented by longitude, latitude) representing the line of intersection
        between the fault plane and the Earth's surface.

- dip:
        Float number. >0 and <= 90.0. Angle between earth surface and fault plane in decimal degrees.

- rake:
        Float number. >=-180.0 and <= 180.0. Angle describing rupture propagation direction in decimal degrees.

----------
The Complex Fault Source is defined by the following additional parameters:

- fault_top_edge:
        3D line (each point in the line represented by longitude, latitude, depth - depth >= 0.0) representing fault surface top edge.

- fault_bottom_edge:
       3D line (each point in the line represented by longitude, latitude, depth - depth >= 0.0) representing fault surface bottom edge.

- fault_intermediate_edges:
       Unbounded (from zero to infinity) sequence of 3D lines (each point in the line represented by longitude, latitude, depth - depth >= 0.0) representing fault surface intermediates edges.

- rake:
        Float number. >=-180.0 and <= 180.0. Angle describing rupture propagation direction in decimal degrees.

[Damiano Monelli (monelli)]

Examples of source data for the 4 different source typologies (point,area,simple fault, complex fault)

[Lars Butler (lars-butler)]

Per conversation with @monelli:

Relax the restrictions on "tectonic region type" elements (in source models, rupture models, and logic trees). We should simply allow any string in the places.

[Lars Butler (lars-butler)]

Update: Just remove the TRT attribute from the rupture model; it's no longer needed.

[Lars Butler (lars-butler)]

Pull request: https://github.com/gem/nrml/pull/20