Geonet Enhances Earthquake Reporting

Geonet have enhanced their earthquake web pages by offering interactive shake maps for reported earthquakes. The shake maps are compiled from instrument data and on-line questionnaires completed by the public.

Until recently, maps showing the amount of shaking caused by the more prominent earthquakes were manually posted as separate reports in the “news” section of Geonet’s website. These reports were compiled from the “felt earthquake” forms completed by visitors to the website, and appeared one or more days after the event.

The latest innovation results in a shake map being produced for every earthquake reported on the site, and has been made possible by a re-writing of the on-line “felt earthquake” software which analyses reports submitted by the public.

The “Shaking Maps” software displays a summary of the felt effects against a map of New Zealand, drawing on information submitted by the public and data drawn from Geonet’s network of seismometers.

Whilst the energy released during an earthquake is reported using the Richter Scale, the intensity of the felt effects is expressed using the Modified Mercalli (MM) scale which combines observed effects (objects swinging, falling), damage to buildings and infrastructure and various human experiences (trouble standing, walking etc).

By moving their cursor across a shake map, visitors to the site can activate pop-ups summarising individual felt reports (represented by round dots) and seismograph data (represented by small squares). Each map contains a layer (changed via a drop-down menu in the top right corner) showing Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV) and Wood_Anderson Amplitude (W-A) calculated from seismometer measurements. A zoom tool allows viewers to look at selected areas of the map in more detail.

Date, time and location information appears below the map, as does a table summarising the earthquake’s felt intensity at reported locations.

A map for the magnitude 5.4 earthquake 50 km north-east of Collingwood on October 9th, which attracted 180 felt reports from the public, can be viewed here.

Shake maps for individual earthquakes can be activated while viewing the details of an earthquake reported on Geonet’s website. Simply click on the “Shaking Map” option in the left hand toolbar to activate the shake map whilst viewing the details page for a selected earthquake.

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