The objective of GDACS is to assess the overall impact of earthquakes (and eventually associated tsunamis) on affected countries. GDACS alert levels aim at drawing attention to an event that might turn out to be serious enough to require international intervention, or, that could overwhelm national authorities’ response capacity.

JRC has established partnerships with seismological organisations around the world that provide real-time data on earthquakes parameters (magnitude, depth and location). As of September 2017, GDACS included the earthquake intensity calculations (USGS shakemaps [1]) in the alerting algorithm. These parameters are used to establish the affected area and calculate the population nearby. A country-wide vulnerability indicator moderates the alert level to take into account the country-specific vulnerability.
GDACS alert levels aim at classifying earthquakes according to the likelihood that the affected societies can no longer cope at national level and will require humanitarian intervention. The final score then considers the level of coping capacity of the affected country or countries, obtained by the INFORM Index [2]. The coping capacity dimension measures the ability of a country to cope with disasters in terms of formal, organized activities and the effort of the country’s government as well as the existing infrastructure, which contribute to the reduction of disaster risk.

The Tsunami Alerting Algorithm

GDACS tsunami alert calculations are triggered by earthquakes that occur in or near the water. The logic for the tsunami alert is based on (1) the magnitude of the earthquake, (2) the depth of the earthquake, (3) the maximum wave height at any coast reach by the tsunami. The first two parameters are used to look up a tsunami wave height calculation in the JRC Tsunami Database (containing over 132000 scenarios).

For each earthquake of magnitude exceeding 6.5 occuring in a location with positive water depth (from ETOPO30), the tsunami database is queried for the closest matching scenario. Scenarios have been calculated for 13800 locations covering tsunamogenic areas (from NOAA database) for magnitudes ranging from 6.5M to 9.5M with steps of 0.25M.
If a scenario is available, the maximum wave height at a coast is retrieved.
The GDACS Alert Score for tsunami relies on the maximum wave height at a coast. As for the Seismic alerting model, the alert score is transformed into an alert level according to the following thresholds:

These values are then corrected for earthquake depth in the same way as for earthquakes.
A new calculation is always started with the tight EQ parameters (taking about 20 minutes), but the alert routine does not take it into account. Rather, the IOC alert Matrix is used (see figure below), based only on magnitude. This fall-back routine, although widely used in tsunami warning centres, results in many false alerts.

For each earthquake of magnitude exceeding 6.5 occuring in a location with positive water depth (from ETOPO30), the tsunami database is queried for the closest matching scenario. Scenarios have been calculated for 13800 locations covering tsunamogenic areas (from NOAA database) for magnitudes ranging from 6.5M to 9.5M with steps of 0.25M.

If a scenario is available, the maximum wave height at a coast is retrieved. If the maximum wave height is greater or equal than 3m, the tsunam alert is Red; if it the height is greater or equal than 1m, the alert is Orange; otherwise, the alert is Green. These values are then corrected for earthquake depth in the same way as for earthquakes2.

If no scenario has been precalculated (only very few cases), a new calculation is started (taking about 20 minutes), but the alert routine does not take it into account. Rather, the IOC alert Matrix is used (see figure below), based only on magnitude. This fall-back routine, although widely used in tsunami warning centres, results in many false alerts.

Results and limitations

Over the years, the GDACS models have been put to the test, with a high user satisfaction. For earthquakes and tsunamis, the most important aspects are timeliness of alerts (as fast as possible) and avoiding false alerts (don’t wake up people if it’s not needed). The first aspect has been improved steadily by forging agreements with regional seismological institutes around the world to push data to GDACS (rather than GDACS scraping data from their web sites). This is most important for timely triggering of tsunami models. The second aspect is ensured by GDACS’s earthquake vulnerability score (which effectively lowers the alert level for countries able to cope with disasters) and the wave-height-based alerting approach for tsunamis (reducing false tsunami alerts by 90%).

Some of the limitations of the approach

GDACS automatic alerts cannot always reliably predict the humanitarian impact of a natural disaster event - this is very difficult to predict even by very sophisticated probabilistic seismic risk assessment tools that take into account detailed exposure and vulnerability data, painstakingly gathered over long time-periods.
GDACS alerting algorithms are empirical in nature and are intended to give a fast and rough warning to people that realise the limitations of automatic systems and of simple “green - orange - red” schemes.
The INFORM Lack of coping capacity Index a simplification of the reality. The main constraints are related to limitations in the methodology and data quality and availability.

Further work

With increasing availability of (real time) data and continuously improving accuracy and detail of models, impact assessment can always improve. GDACS is a collaboration platform open to organisations that have data, models or systems that can significantly contribute towards better impact assessment and new information for emergency responders.

In the past 5-10 years, seismic risk assessment tools have moved into increasing sophistication and detail and are able to take full advantage of the newest developments in hazard, exposure and vulnerability data. All systems are non-commercial and most are open-source and their components can be freely downloaded. The common approach based on the risk equation renders them easily interoperable, but on the other hand this entails significant duplication of effort.

Most systems are either ready or are adapting fast to a real-time use, as early impact assessment and warning mechanisms. Additionally, the lack of accurate globally available exposure and vulnerability data is hampering this effort, so a joint effort to collect these data sets would be an enormous benefit to the global risk assessment and – eventually – risk reduction effort.

JRC, as the scientific lead in GDACS, is interested in exploring integration of such products in the existing impact models.

With regards to earthquakes and tsunamis, we are currently moving towards a more comprehensive and transparent process by:

The inclusion of the output of at least two seismic risk assessment systems in the GDACS events pages with an automatic calculation after an event, or by a manual update by the system developers in a dedicated space.
The integration of probabilistic models and the assessment of the uncertainty, e.g. in relation to the following factors: (i) preliminary uncertainty related to the variation of initial parameters (Mw, depth, location); (ii) number of previous deadly events used to calculate the country seismic vulnerability; (iii) differences in the exposed population due to the use of different global datasets e.g. LandScan and GHSL). This would allow to define and communicate the “alert uncertainty” based on the parameters used to calculate the GDACS alert score.

Additionally, the increase of accurate globally available exposure and vulnerability data is supporting this scope, so the joint effort to collect these data sets is providing an enormous benefit to the global risk assessment and – eventually – risk reduction effort.