Glossary of Terms#

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


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


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)

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


A unique set of input files for which we attempt to produce results. Input files include an INI-style config file (containing various calculation parameters) and various XML files. The structure of these XML files is defined by our XML specification: NRML. The quantity, type, and content of these XML files will vary depending on the calculation mode.

The terms calculation and job are often used synonymously, but it is important to understand the distinction.


A Python class which can implement various methods associated with each calculation phase. In order of execution, the phases are:

  • pre_execute

  • execute (this is the only required method)

  • post_execute

  • post_process

  • export

  • clean_up

Each calculation mode has its own calculator class defined, although many common functionalities are shared between calculators. This common functionality is abstracted into common base classes and plain functions.

Configuration File#

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

Consequence Function#

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

Consequence Model#

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

Control Node#

The machine from which the user initiates a calculation. The control is responsible for running code which processes user input, initializes a calculation, distributes work, and manages/monitors the calculation until completion.

By convention, the machine used as the control node does not process tasks. The control node is also typically the machine which runs vital server processes, such as RabbitMQ, and PostgreSQL/PostGIS.

Characteristic Fault Source#

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

Complex Fault Source#

A source typology usually adopted to model subduction interface faults


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

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)


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

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

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

Earthquake Rupture Forecast Calculator#

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


The term “engine” refers to the OpenQuake engine, the piece of software which is responsible for reading inputs, distributing calculations, and collecting outputs.


normalized residual of the ground motion

Exposure Model#

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

Fault Trace#

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


Fig. x.x Single rupture#

Fragility Function#

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

Fragility Model#

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

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

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)

Ground-Motion Field (GMF)#

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

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

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

Ground-Motion Model#

An object that given a rupture with specific properties computes 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

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.

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

Ground-Motion System#

An object containing a list of Ground-Motion Logic Trees

Initial Seismic Source Input Model#

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

Insured Losses#

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

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 the GEM Foundation and the Center for Disaster Management and Risk Reduction Technology, and it has been developed by the GEM Foundation.

Investigation Time#

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


The runtime “thing” which represents an attempt to complete a calculation. The job contains various pieces of information which are relevant while a calculation is in progress, including:

  • status (i.e., “Is it running?”, as well as the calculation phase)

  • logging level

  • the user who initiated/owns this job

  • engine process IDs

If in the future calculation resumability is supported, there could be more than 1 job associated with a calculation.


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

Logic Tree#

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

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

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)

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

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

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


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

OpenQuake Hazard Library#

The OpenQuake Hazard Library (openquake.hazardlib) is the Python library the OpenQuake engine team has developed to function as the core scientific library behind the OpenQuake engine for Seismic Hazard.

OpenQuake Risk Library#

The OpenQuake Risk Library (openquake.risklib) is the Python library the OpenQuake engine team has developed to function as the core scientific library behind the OpenQuake engine for Seismic Risk.

Point Source#

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

PSHA Input Model#

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

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

Earthquake Rupture#

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

Rupture Model#

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

Rupture Aspect Ratio#

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


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

Scenario Based SHA#

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

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

Seismicity Rate#

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

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

Seismic Source Logic Tree#

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

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

Seismic Source#

An object that can generate SHOULD BE COMPLETED

Seismic Source Model (SSM)#

An object containing a list of Seismic Source objects

Seismic Source System#

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

Simple Fault Source#

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

Stochastic Event Set#

An object containing one or many Seismicity History


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


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 used in the post-processing stage of a risk calculation to aggregate results for each tag.


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 its material, height, year of construction. The taxonomy is currently used to link the Asset in the Exposure Model to the relevant Vulnerability Function or Fragility Function

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

Temporal Occurrence Model#

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

Vulnerability Function#

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

Vulnerability Model#

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


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

Worker Process#

A process which is dedicated to task execution.

Worker Machine#

A machine dedicated to run worker processes.

The concepts of “worker machines” and “worker processes” are often referred to synonymously (as “workers”, for short). Technically, there can be many worker processes running on a single worker machine. The number of worker processes per machine is typically equal to the number of CPU cores available.