Openquake 0.1 hazard input

An OpenQuake PSHA Input Model contains a Seismic Sources System and a Ground Motion Prediction Equations System. A Seismic Sources System contains one (or several) Initial Seismic Sources Model and a logic tree structure describing epistemic uncertainties connected with the definition of the Earthquake Rupture Forecast. A Ground Motion Prediction Equation System contains the logic tree structure describing epistemic uncertainties connected with the use of Ground Motion Prediction Equations in the tectonic regions used to characterise the Seismic Sources included in the Seismic Sources System.

Notes

A Seismic Source Model consists of a collection of seismic sources (without any epistemic uncertainty). Each source type is characterized by three common parameters: ID, name, and a tectonic region type. So far, four source typologies are considered:

• Area (a polygonal geographic region with uniform seismicity). An area source is characterized by the following parameters:

  • region outer border
  • one or more magnitude frequency distributions, each associated to a focal mechanism
  • average top of rupture depth versus magnitude
  • average hypocentral depth

• Grid (arbitrarily shaped grid with varying seismicity). A grid source is defined in terms of multiple point sources, each characterized by the following parameters:

  • location coordinates
  • one or more magnitude frequency distributions, each associated to a focal mechanism
  • average top of rupture depth versus magnitude
  • average hypocentral depth

• Simple Fault (rectangular 3D surface for simple fault representation). The required parameters are:

  • fault trace coordinates
  • dip angle
  • rake angle
  • lower seismogenic depth
  • upper seismogenic depth
  • magnitude frequency distribution

• Complex Fault (irregular 3D surface for complex fault representation)

  • fault top edge coordinates
  • fault bottom edge coordinates
  • fault rake angle
  • magnitude frequency distribution

A magnitude frequency distribution can be of three types:

1. truncated Gutenberg-Richter
2. Gaussian
3. generic evenly-discretized, incremental magnitude frequency distribution

While simple fault and complex fault sources can assume all the three types of magnitude frequency distributions, area sources and grid sources can assume only type 1 and 3.

Tectonic region types can be of five typologies:

• Shallow Active Crust

• Stable Continental

• Subduction Interface

• Subduction Intraslab

• Volcanic

A Ground Motion Prediction Equations model contains as a set of ground motion prediction equations (GMPEs) each corresponding to a tectonic region type defined in the seismicity source model. In the simplest case where only one tectonic region type is considered, the ground motion model will be defined by only one set of GMPEs.

Epistemic uncertainties (expressing scientific uncertainties due to limited data and knowledge) are expressed through a logic tree structure. A logic tree consists of one or more branching levels, each containing one or more branch sets. A branch sets contains one or more branches, each defining an uncertainty value.

To describe epistemic uncertainties in the Seismic Sources System, multiple (alternative) initial Seismic Sources Models can be defined in the first branching level. Subsequent branching levels can be used to describe uncertainties on specific parameters.

To describe epistemic uncertainties in the Ground Motion Prediction Equations System, a logic tree consisting of a single branching level describing the possible GMPEs is defined for each tectonic region type.

There's a number of features we're planning to implement within the next few months with respect to the definition of input information and its support in OpenQuake. In particular we would like to:

1. Extend the standard Hazard Input Model description by adding new source typologies and more flexible definitions of frequency-magnitude distributions and temporal occurrence model;
2. Better support the description of Site properties by allowing the specification of site specific parameters (e.g. VS,30);
3. Extend the standard Hazard Input Model description by adding more comprehensive ways of describing the structure of a logic tree (e.g. general rules Vs source specific rules a la Coppersmith et al., 2009).

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