about earthquakes in the Groningen gas field, the Netherlands

Richter in Groningen

and why the Richter scale does not provide a complete picture

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by Kor Dwarshuis

Last update: oct 6th. 2015, 19:07 pm

“Why are they complaining in Groningen? A quake of 3.6 on the Richter scale is peanuts.
8 on the Richter scale, now THAT is a quake!!”

That is correct

Groningen does not have quakes of 8 on the Richter scale with thousands of casualties.

There is every reason to be worried, however.

The quakes caused by gas extraction differ from natural earthquakes. For this reason, the Richter scale does not provide a complete picture.

There are

4 differences

between normal natural earthquakes

and the induced (= man-made) quakes in Groningen.

Because of these differences the quakes in Groningen are not as innocent as Richter would have us believe.

The four differences:

depth
accumulation
clay
buildings

1. Depth

Shallow gas quakes release more energy to the surface than natural deep quakes.

Richter 3.6

3.6 Richter

‘Gas quakes’ 1 to 3 km

Natural quakes 20 to 100 km

Ergo: a natural earthquake of 3.6 has less impact than a gas quake of 3.6.

2. Accumulation

Together, many small earthquakes form one big quake.

Most quakes in Groningen are light. A light quake does not have big effects, but all those small accumulated quakes do.

3. clay

The soil in the quake zone consists of soft clay.

The clay behaves like a giant rubber band and has the potential of aggravating the quakes. This is called resonant rise.

The Groningen clay is a blessing for the grain yield, but a curse in relation to the earthquakes.

4. Buildings

Dense urban development can dampen a quake.

In the empty countryside, a quake can spread widely with resonant rise until it reaches a village.

Eyewitnesses say they have seen the countryside ripple into the distance.

In summary:

1.

A gas quake of 3.6 is not as devastating as a natural earthquake of 8.0, but much worse than a natural earthquake of 3.6.

In summary:

2.

Together, many small earthquakes form one big quake.

In summary:

3.

The Richter scale does not take into account the four factors mentioned earlier.

Conclusion

For a fair indexation of earthquakes in Groningen a better scale is required - one that includes factors such as depth, accumulation, soil and buildings in the equation.

Take a look at a story about the history of the Groningen gas field.

Credits

Based on information from Groninger Bodem Beweging.

and the NAM: http://www.nam.nl/content/dam/shell/static/nam/downloads/pdf/brochure-lichteaardbevingen.pdf, pagina 3

#2 (cumulation) explained by Manuel Sintubin on EenVandaag (Dutch): http://www.npo.nl/eenvandaag/16-12-2014/AT_2023867?start_at=630, at 10 min 28 sec

Animation of the resonant rise: bogotobogo, adapted by Kor Dwarshuis.

Images: 1