Short-term preparation: monitoring

Risk maps are good tools to make long-term preparations for natural hazards.

But they do not directly help with evacuations or other risk mitigation strategies that result from imminent or ongoing natural hazards.

This is because they do not contain information on when the next natural hazard will occur in the future.

In order to be able to make short-term preparation such as an evacuation, we need to monitor the faults, volcanoes, and other sources of natural hazards. We can do this with all sorts of instrumentation.

Seismometer

A crucial instrument for both earthquakes and volcanoes, is the seismometer.

This is an instrument used to record the motion of the ground during an earthquake. They are installed in the ground throughout the world and operated as part of a seismographic network.

Seismometer networks can be used as an early warning system for earthquakes. It is currently not possible to give advanced warning for an earthquake.

But, depending on your distance to the epicenter, it is possible to give a warning signal of seconds to tens of seconds before the severe shaking occurs.

ShakeAlert is such an early warning system that was developed in California.

You might like to watch this video of ShakeAlert explaining how it works.

Volcanic eruptions are often preceded by many changes underneath the surface that can be picked up by a range of instruments, including seismometers. So, unlike earthquakes, there is a lot higher chance that we can take action before an eruption, provided there is sufficient monitoring of erupting volcano.

At the same time, observations of subsurface activity does not always indicate an imminent eruption. The challenge here lays in the correct interpretation of seismic and other signals to identify the physical processes that are occurring.

2000 Hekla eruption, Iceland

The most successful volcanic eruption forecast was that of the Icelandic volcano, Hekla when it erupted in February 2000.

Small earthquakes were detected with Moment magnitude smaller than 1 starting at 17:07 on February 26, 2000.

At 17:30 ground deformation was being measured. These signals closely followed a pattern of a Hekla eruption in 1991. At 17:53 a warning was issued on the national radio that an eruption was to start at Hekla in 15 minutes; 17 minutes later it erupted.

The key elements of this success were:

1. Monitoring tools such as seismometers were present at the volcano.
2. The observation followed closely the pattern of a previous eruption.
3. An observational record that goes back long enough in time.

By combining long-term and short-term risk preparation techniques, we are able to make communities more resilient against future natural hazards.