The earthquakes near Uithuizen and Uithuizermeed led to more than fifty damage reports on Saturday. Why is it that the earthquakes in Groningen cause so much damage?
According to the explanation of the Richter scale the earthquakes in Groningen mean little. Quakes to a strength of 2.9 on this scale almost never cause damage and tremors with a magnitude of 3.0 until 3.9 provide at most some loose roof tiles. Most earthquakes in Groningen are much lighter. Yet they cause serious damage to buildings. That has two causes.
The earthquakes in Groningen originate at a shallow depth
The earthquakes in Groningen originate in the gas field at a depth of only three kilometers. The shock waves lose little energy during their short journey to the surface. Natural earthquakes occur at depths of ten kilometers and more. Their shockwaves lose much more energy along the way.
The Groningen soil is weak
The soil under Groningen partly consists of peat and clay. This soft ground moves easily. A relatively light earthquake can already cause a strong ground movement (and thus damage) to the surface. Local differences in the soil composition mean that the damage in one place can be much greater than in another nearby place.
The Richter scale
The numbers on this logarithmic scale expresses the strength of an earthquake. With each step on the scale, the tremor gets ten times stronger. A tremor with strength 3 is therefore ten times stronger than a strong quake 2. And a tremor of 3.1 is more than one and a half times stronger than an earthquake of 2.9.