There is no way to carry out an underground nuclear test in secret. It is no use denying it, because seismic waves are registered around the world, and the collected data is open for everyone.

All shocks on Earth are registered in earthquake data, which is collected communally. The data collected in Finland is also transmitted to the international network.

The ubiquitous data that is collected from many different locations can prevent bluffs and sharpen our observations of natural phenomena and human actions. It has been useful for investigating accidents and planning rescue operations.

How was the crash site of the Finnish Air Forces Hornet found?

A little before noon in January 2010, for example, a Hornet fighter plane crashed into the ground north of Tampere.


M. Tarvainen et al. / Natural Science 5 (2013) 811-817


Based on the observations by the Finnish seismograph stations, the crash site could be pinpointed to within a few kilometres’ accuracy.   Source: Seismic analysis of aircraft accidents, M. Tarvainen et al. 2013.

The collapse of the WTC towers in New York or the sinking of a nuclear submarine in the Sea of Barents can be seen in seismic data that can be accessed and analysed by anyone. On the other hand, if there is no seismic data available, it tells us something about the accident and its consequences.

What if Earth is flat, after all?

The signal from an earthquake in Mexico spreads in different directions and weaves its way to Finland. The wave caused by the earthquake is observed several times. The observations are registered in open data, and by studying that we have learned more about the structure of Earth.

“Some of the seismic waves also travel through the core of the Earth, but the quickest route for the seismic wave does not usually go through the core, but along the mantle. This is one way of proving that the Earth is not flat,“ says seismologist Aleksi Aalto from the Institute of Seismology at the University of Helsinki.

How the seismic wave travels

In the mantle, a seismic wave travels about 8-14 kilometres per second, and in the core, 8-11 kilometres per second. This means that the quickest wave arrives by avoiding the core, since the sound velocity is faster in the mantle. In air, sound travels some 343 metres per second, for example, and in water, some 1,500 metres per second. Thus, the velocity is much faster in stone.

For all the observations to fit together, researchers have concluded that the refraction and reflection of the signal is caused by the changing velocity of the seismic wave, and its collisions with the inner strata of Earth.

This has led to the conclusion that there are a lot of strata inside Earth, where the thickness of materia and the velocity of a seismic wave vary. And Earth must be round.

“The laws of physics and open data combined prove that the observations that Earth is round are true“, says Aalto.

Earthquake data draws a picture of continental plates

The Faculty of Science has collaborated with Exove Design to make the VR video Journey to the Centre of the Earth, an introduction to scientific research and recording observations of the universe. Aleksi Aalto tells us how the video was made.

"The data archived over earthquakes the past forty years, their strengths and locations, were compiled in one picture. Based on this data, we could form the illustration of the continental plates seen in the VR video", says Aalto.

Edges of the continental plates cross oceans and reveal where earthquakes are most likely to occur in future.

Do you want to study earthquakes observed in Finland on your own?

Start here

Nearly 13,000 seismic occurences in Northern Europe are analysed every year at the Institute of Seismology. Out of them, 1-3 percent are earthquakes, the rest are industrial explosions. In addition, over 3,000 earthquakes from other parts of the world are analysed. The analysis of seismic events includes identification and location of the events and determining the strength and depth of them.