# 6. Glossary#

## 6.1. Area Source#

A source type usually adopted to model distributed seismicity. In an area source the seismicity occurrence rate is assumed uniform over the source area; this produces an hazard pattern with aplateau of constant hazard inside the polygon delimiting the area sourceand values of hazard that tend to decrease as we move away from the border of the source

## 6.2. Asset#

An asset is an element with a certain value, which can include buildings or
population. For example, an asset can include an individual building at a
given location, or a number of buildings that are grouped, co- located at a
single location and classified with the same *Taxonomy*

## 6.3. Branch#

The simplest element in a logic tree; it belongs to a *Branch Set* where it
represents one possible option among a finite number of alternatives. A branch
is associated with a weight value if the *Branch Set* represents the
epistemic uncertainty on a parameter or a model when the *Branch Set* is
used to specify alternative models (e.g. district
*Magnitude-Frequency Distribution*)

## 6.4. Branch Set#

The structure describing the epistemic uncertainty on a specific parameter or
model included in a logic tree structure. It ensembles a number of *Branch*,
each one representing a discrete alternative

## 6.5. Configuration File#

The file (usually .ini) containing the information necessary to run a calculation in OpenQuake

## 6.6. Consequence Function#

the distribution of the consequence (or loss) ratio conditional on a set of
discrete limit states, defined for a particular *Taxonomy*

## 6.7. Consequence Model#

A set of *Consequence Function* used to model the consequence ratios of all
the *Taxonomy* in the *Exposure Model*

## 6.8. Characteristic Fault Source#

A fault source typology where ruptures always cover the entire fault surface

## 6.9. Complex Fault Source#

A source typology usually adopted to model subduction interface faults

## 6.10. Deductible#

A parameter used in the calculation of insured losses thatestablishes the economic value that needs to be deducted from the ground-up losses

## 6.11. Seismic Hazard Disaggregation#

A methodology to investigate the contributions to aspecific level of hazard in
terms of fundamental variables commonly usedto characterize seismic sources
and ground motion models (e.g. magnitude, source-site distance, *Epsilon*

## 6.12. Dip#

The dip is the steepest angle of descent of the fault plane relative to a horizontal plane; it is measured in degrees [0,90]

## 6.13. Disaggregation Matrix#

A multi-dimensional matrix used to systematically store thecontributions to a
level of hazard to be disaggregated and that is specified by the user.
See also *Seismic Hazard Disaggregation*

## 6.14. Earthquake Rupture Forecast#

A list of all possible ruptures generated by all thesources included in a seismic source model. Each element in the listcontains: the rupture geometry and the rupture probability of occurrencein a given time span. See also the definition available on the OpenSHA website

## 6.15. Earthquake Rupture Forecast Calculator#

Calculator producing a *Seismic Source Model* from a
*Seismic Source Logic Tree*

## 6.16. Epsilon#

normalized residual of the ground motion

## 6.17. Exposure Model#

A set of *Asset* grouped according to their geographical location, *Taxonomy*
and value

## 6.18. Fault Trace#

A curve representing the intersection between the surface containing the fault surface (or its prolongation) and the topographic surface

## 6.19. Fragility Function#

the probability of exceeding a set of limit states, given an intensity measure level. These functions can be discrete or continuous

## 6.20. Fragility Model#

A set of *Vulnerability Function* used to model the fragility of all the
*Asset* in the *Exposure Model*

## 6.21. Frequency-Magnitude Distribution#

A distribution describing the frequency of earthquakes with a specific magnitude. It can be continuous or discrete. One frequency- magnitude distribution frequently adopted in PSHA is the double truncated Gutenberg-Richter distribution

## 6.22. Grid Source#

A source typology usually adopted to model distributedseismicity. It is routinely produced by a seismicity smoothing algorithm (one of the most famous algorithm is the one proposed by Frankel 1995)

## 6.23. Ground-Motion Field (GMF)#

An object describing the geographic distribution around a rupture of a ground motion intensity measure

## 6.24. Ground-Motion Field Calculator#

An OpenQuake engine calculator that given a rupture computes thegeographic
distribution of a ground motion intensity parameter. Currently OQ can
generate ground motion fields using a *Ground-Motion Prediction Equation*

## 6.25. Ground-Motion Logic Tree#

A method used to systematically describe the epistemicuncertainties related
to the ground motion models used in the computation of hazard using a
specific *PSHA Input Model*

## 6.26. Ground-Motion Model#

An object that given a rupture with specific propertiescomputes the expected
ground motion at the given site. In simplest case aground motion model
corresponds to a *Ground-Motion Prediction Equation*. Incase of complex PSHA
input models, the produced ground motion models contains a set of
*Ground-Motion Prediction Equations*, one for each tectonic region considered

## 6.27. Ground-Motion Parameter#

A scalar or vector quantity describing a relevant propertyof the shaking such as intensity (e.g. PGA or Spectral Acceleration)or duration, equivalent number of cycles. See for example Hancock 2005.

## 6.28. Ground-Motion Prediction Equation (GMPE)#

An equation that - given some fundamental parameters characterizing the
source, the propagation path and the site (in thesimplest case magnitude,
distance and *VS30* - computes the value GM of a (scalar) ground
motion intensity parameter

## 6.29. Ground-Motion System#

An object containing a list of *Ground-Motion Logic Trees*

## 6.30. Initial Seismic Source Input Model#

It is the ensable of information needed to fully describethe seismic sources composing a seismic source input model. Theinitial seismic source input model is included in the first branching level of a seismic source logic tree

## 6.31. Insured Losses#

Fraction of the ground-up losses that can be covered by the insurance industry, according to a certain policy

## 6.32. Integrated Risk Modelling Toolkit#

A plugin for QGIS which includes tools to run the OpenQuake Engine,to visualize hazard and risk results, to develop composite indicatorsand integrate them with physical risk estimations, and to predict building recovery times following an earthquake.This plugin was designed as a collaborative effort between theGEM Foundation and the Center for Disaster Management and Risk Reduction Technology, and it has been developed by the GEM Foundation.

## 6.33. Investigation Time#

The time interval considered to calculate hazard; usually it corresponds to 50 years

## 6.34. Limit#

A parameter used in the calculation of insured losses thatestablishes the maximum economic amount that can be covered by the insurance industry, according to a certain insurance policy

## 6.35. Logic Tree#

Data structure used to systematically describe uncertainties on parameters and models used in a PSHA study

## 6.36. Logic Tree Processor#

An OQ calculator that takes the PSHA Input Model and createsmany
realisations of a *Seismic Source Model* and of a *Ground-Motion Model*

## 6.37. Magnitude-Scaling Relationship#

An empirical relationship linking the magnitude with a parameter describing the size of the corresponding rupture (e.g. the area of the rupture or the rupture length)

## 6.38. Magnitude-Frequency Distribution#

A distribution describing the frequency of earthquakes with a specific
magnitude. It can be continuous or discrete. One frequency-magnitude
distribution frequently adopted in *PSHA* is the double truncated
Gutenberg-Richter distribution

## 6.39. Non-Parametric Source#

A source typology in which the earthquake rupture forecast isdescribed explicitly by a set of ruptures and the corresponding probabilities of occurrence

## 6.40. Natural Hazards’ Risk Markup Language#

A markup language similar to XML, which specifies a numberof standardised schemas to represent various input models used for OpenQuake engine calculations and output files generated by the OpenQuake engine

## 6.41. OpenSHA#

OpenSHA is an open-source, advanced Java-based platformfor conducting Seismic Hazard Analysis - (see the OpenSHA website)

## 6.42. Point Source#

The elemental source typology used in the OpenQuake Engine to model distributed seismicity

## 6.43. PSHA Input Model#

An object containing the information necessary to describethe seismic source and the ground motion models - plus the related epistemic uncertainties

## 6.44. Probabilistic Seismic Hazard Analysis (PSHA)#

A methodology to compute seismic hazard by taking intoaccount the potential contributions coming from all the sources of engineering importance for a specified site

## 6.45. Earthquake Rupture#

A 3D surface - representing a portion or the entire fault surface - over which a slip event (i.e. an earthquake) occurs

## 6.46. Rupture Model#

An object containing the information necessary to describe a *Rupture*,
such as magnitude, hypocenter location, strike, dip, rake, and seismogenic
depths

## 6.47. Rupture Aspect Ratio#

The ratio between the lenght and the width of an earthquake rupture

## 6.48. Rake#

The rake is the direction in which a hanging wall block movesduring a rupture, measured relative to fault strike on the plane of the fault

## 6.49. Scenario Based Seismic Hazard Analysis#

An analyis of seismic hazard based on the selection ofone or a few ruptures
and the computation of the expected groundmotion at a set of sites using a
*GMPE* accounting ground motion variability

## 6.50. Seismicity History#

An object containing a set ruptures representative of thepossible seismicity
generated by the sources in a *Seismic Source Model* during the investigation
time $t$

## 6.51. Seismicity Rate#

Number of events per unit of time (if not betterspecified, the definition of a seismicity rate generally presumes a time independent

## 6.52. Seismic Source Data#

An object containing the information necessary tocompletely describe a
*PSHA* seismic source i.e. seismic source type, position, geometry and
seismicity occurrence model

## 6.53. Seismic Source Logic Tree#

Logic tree structure defined to describe in structured and systematic way
the epistemic uncertainties characterizing the seismicsource model. The first
branching level in the logic tree by definition contains one or several
alternative *Initial Seismic Source Input Model*

## 6.54. Seismic Source Input Model#

An object containing a list of *Seismic Source Data*. In the OpenQuake Engine
a seismic source model does not contain epistemic uncertainty

## 6.55. Seismic Source#

An object that can generate

## 6.56. Seismic Source Model (SSM)#

An object containing a list of *Seismic Source* objects

## 6.57. Seismic Source System#

An object containing a list of *Initial Seismic Source Input Model*
and the *Seismic Source Logic Tree*

## 6.58. Simple Fault Source#

A source typology usually adopted to model shallow structures with an uncomplicated geometry

## 6.59. Stochastic Event Set#

An object containing one or many *Seismicity History*

## 6.60. Strike#

The strike direction correspond to the angle between thenorth and the
direction you take so that when you walk along the *Fault Trace*
the fault dips on your right

## 6.61. Tag#

Scheme used to specify attributes for the *Asset*. Attributes for an *Asset*
could include the state, county, zip-code,city, occupancy, CRESTA ID, or
other such markers that could be usedin the post-processing stage of a risk
calculation to aggregate results for each tag.

## 6.62. Taxonomy#

Scheme used to classify the *Asset*. For buildings, a classification
scheme has been proposed by the GEM Foundation which considers anumber of
attributes including lateral load resisting system and itsmaterial, height,
year of construction. The taxonomy is currently used tolink the *Asset*
in the *Exposure Model* to the relevant *Vulnerability Function* or
*Fragility Function*

## 6.63. Tectonic Region#

A area on the topographic surface that can be considered homogeneous in terms of tectonic properties such as the prevalent seismogenic properties and/or the seismic wave propagation properties

## 6.64. Temporal Occurrence Model#

Usually a probabilistic model giving the probability of occurrence of an
event in a specified *Investigation Time*

## 6.65. Vulnerability Function#

A function that describes the probability distribution ofloss ratio, conditioned on an intensity measure level. Currently only discrete vulnerability functions are supported

## 6.66. Vulnerability Model#

A set of *Vulnerability Function* used to model the physical vulnerability
of all the *Asset* in the *Exposure Model*

## 6.67. VS30#

Average shear wave velocity of the materials in the uppermost 30m of the soil column