Hazard map

Earthquakes: seismic aspects


seismic
Maps produced during a humanitarian response to earthquakes, visualising the seismic data and any data that may forecast the extent of physical damage and potentially act as a proxy for humanitarian impact. It may be combined with other thematic layers, notably with baseline population data to enable a rapid/early analysis of the population potentially affected.
Strategic or operational?

Both

Basemap, baseline or situational?

Situational.

When might it be produced?

At an early stage after the occurrence of a major earthquake with the potential to create damage and casualties. The necessary data will invariably be available within hours of the initial earthquake. Data and maps may be updated following aftershocks or to add additional analysis layers, including for example assessed landslide risk zones, vulnerable infrastructure (e.g. dams), or population baselines.

Intended audience

All responders, but particularly those operating across the wider affected area, and including actors working on assessment processes and response planning and coordination.

Influence on humanitarian decisions

Initial data, typically from United States Geological Survey Earthquake alerts, will give basic indicators including the magnitude and location of the epicentre of the initial event and any aftershocks. This point data should be placed on the map first. It is not good practice to buffer circular rings around the epicentre, as this may imply a spatially regular fall-off of damage that is very unlikely to reflect reality. As a large earthquake is “more appropriately described as a slip over a larger fault area” (United States Geological Survey, see below), single points are poor representations of large earthquakes, so a map showing zones of ‘shake intensity’ provides more useful information. Analysed shake intensity zone data should be obtained and mapped as soon as possible. Because this is modelled predictively rather than ground-truthed, it should be appropriately explained and caveated on maps. A suitable base map will normally include terrain and any available data on population distribution or population places.

Initial data, typically from United States Geological Survey (USGS) Earthquake alerts, will give basic indicators including the magnitude and location of the epicentre of the initial event and any aftershocks. This point data should be placed on the map first. It is not good practice to buffer circular rings around the epicentre as this may imply a spatially regular fall-off of damage which is very unlikely to reflect reality. As a large earthquake is “more appropriately described as a slip over a larger fault area” (USGS, see below), single points are poor representations of large earthquakes, so a map showing zones of ‘shake intensity’ provides more useful information. Analysed shake intensity zone data should be obtained mapped as soon as possible. Because this is modelled predictively rather and not ground-truthed, it should be appropriately explained and caveated on maps. A suitable base map will normally include terrain and any available data on population distribution or population places.

  • Geophysical data is usually obtained from United States Geological Survey or others. This may include locations of reported epicentres of primary and aftershocks (as points), and modelled shake intensity (as polygons).
  • Data on predicted or actual landslides from various providers; but be cautious of the methods used to derive these as they may not be reliable.
  • Analysed satellite imagery to identify building damage; but be cautious because analysis methods may not have been standardised or reliable, and take special care to identify areas that have not been analysed.

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