Multi-peril scenario damage

A multi-peril damage calculation evaluates primary ground shaking and one or more earthquake-triggered secondary perils in the same scenario. For example, the engine can calculate ground-shaking, landslide, and liquefaction damage to the same assets and use the results in an infrastructure connectivity analysis.

This workflow uses the normal scenario_damage calculation mode. It does not use multi_risk, which is a separate calculator retained for other multi-hazard applications.

How the inputs fit together

A multi-peril calculation adds three relationships to a standard scenario damage model:

1. secondary_perils selects the models that derive secondary intensity measures from the earthquake ground motions and site parameters.

2. A separate fragility file relates each peril’s intensity measure to damage states.

3. The taxonomy mapping and, when used, the consequence model identify the peril to which each row applies.

The relevant parts of job.ini look like this:

[general]
calculation_mode = scenario_damage

[site_params]
site_model_file = site_model.csv

[perils]
secondary_perils = Jibson2007BLandslides,
    AllstadtEtAl2022Liquefaction

[calculation]
intensity_measure_types = PGA, PGV, SA(0.3)

[exposure]
exposure_file = exposure.xml
taxonomy_mapping_csv = taxonomy_mapping.csv

[fragility]
groundshaking_fragility_file = {
    "structural": "fragility_groundshaking.xml"}
landslide_fragility_file = {
    "structural": "fragility_landslide.xml"}
liquefaction_fragility_file = {
    "structural": "fragility_liquefaction.xml"}

[consequence]
consequence_file = {'taxonomy': 'consequences.csv'}

The prefix of each fragility parameter is the peril name used throughout the risk model. groundshaking is the primary peril. The secondary fragility functions use the intensity measure produced by the selected secondary-peril model; for example, the maintained demo uses Disp for landslides and LSE for liquefaction.

The taxonomy mapping needs one row for every applicable taxonomy and peril:

taxonomy,risk_id,weight,peril
bridge,bridge1,1,groundshaking
bridge,bridge1,1,landslide
bridge,bridge1,1,liquefaction

The risk_id must identify a function in the corresponding fragility file. If consequences are required, their CSV rows use the same risk IDs and perils:

risk_id,consequence,peril,slight,moderate,extensive,complete
bridge1,non_operational,groundshaking,0,0,1,1
bridge1,non_operational,landslide,0,0,0,1
bridge1,non_operational,liquefaction,0,0,0,1

See Secondary perils for the intensity measures and site parameters required by each secondary-peril model. See Consequence Models for the complete consequence file format.

Consistency checks and modelling choices

Before running the calculation, check that:

• every fragility model uses the same limit-state names in the same order;

• the ground-motion calculation includes all primary intensity measures needed by both the ground-shaking fragilities and secondary-peril models;

• each secondary fragility uses an intensity measure produced by its selected secondary-peril model;

• every applicable exposure taxonomy maps to a valid risk ID for each peril; and

• consequence rows, when supplied, cover the required risk IDs and perils.

Review warnings about secondary intensity measures being discarded below minimum_intensity. A threshold that is too high can bias the damage results.

Asset Risk Distributions and Asset Risk Statistics preserve the result for each peril. Ground-shaking columns use names such as structural-complete; secondary-peril columns are prefixed, for example landslide-structural-complete and liquefaction-structural-complete.

For risk_by_event and the aggregate damage outputs, the engine composes the per-peril damage distributions. For each damage-state exceedance probability \(p_i\), the combined value is \(1 - \prod_i (1 - p_i)\). Consequences are combined by taking the maximum value across the perils for each asset and event. These are modelling assumptions rather than a joint fragility model; assess whether they are appropriate for the intended application. Infrastructure connectivity analysis uses these composed event results.

Maintained example

The InfrastructureMultiPeril demo contains a complete ground-shaking, landslide, and liquefaction scenario for a small road network. From a checkout of the engine repository, run it with:

oq engine --run demos/risk/InfrastructureMultiPeril/job.ini
oq engine --list-outputs -1
oq engine --export-outputs -1 results