This year marks the 100th anniversary of seismological measurements in Finland.
In honor of the anniversary, the researchers of the Institute of Seismology publish a biweekly blog on a current or otherwise interesting topic related to seismology and research conducted in the institute. I have the honor to start the blog series by introducing the activities of the institute in general.
Seismological observation began in Finland in 1924, when the Finnish Society of Sciences and Letters donated the first seismograph to the University of Helsinki.. A seismograph is a device used to measure the vibrations of the earth’s crust. In 1961, almost 40 years after donation of first seismograph, the Institute of Seismology was founded. The foundation of the Institute was driven by an increasing need for seismic monitoring because of the Soviet Union’s nuclear tests on Novaya Zemlya. Nuclear tests, like other explosions, cause seismic waves that propagate through the earth’s crust like earthquakes. Explosions and earthquakes are typically easy to distinguish from each other based on the waveform, as the generation mechanisms of these events are physically different. In an explosion, the energy travels uniformly in all directions from a point source, while the wave front caused by an earthquake is asymmetrical. In the explosion recordings, the first ground motion is always upward, regardless of the seismograph’s location. In an earthquake, on the other hand, the different sides of the fault zone move relative to each other, as a result of which the ground movement can be either up or down, depending on the position of the seismograph in relation to the origin of the earthquake, the epicenter. The current global network of seismographs enables the detection of seismic events with a magnitude greater than 3.5 all around the world, so monitoring underground nuclear tests using seismological methods is also effective. Due to its location, Finland is an important part of seismic monitoring.
Finland’s seismic network currently includes more than 40 permanent stations around the country. In addition, the Institute of Seismology uses data from the stations maintained by the Sodankylä Geophysical Observatory in Northern Finland. With the help of the seismic network, we can detect and locate significant earthquakes around the world. The Institute of Seismology delivers earthquake warnings to the Natural Disasters Warning System (LUOVA). In particular, we inform the authorities about large earthquakes that may have caused severe damage to populated areas. Earthquakes that occur under the sea are analyzed quickly and accurately because of the tsunami danger. In addition to global cases, the national network also monitors the seismicity of our nearby areas. In Finland, earthquakes are small, but especially in the Rapakivi areas in Kymenlaakso and Åland, as well as in the Kuusamo area, earthquakes are relatively common. The Institute of Seismology receives observations of earthquakes from citizens every year, which are often confirmed to be correct by analysis of the recorded seismic data.
In addition to maintaining and developing the national seismic network, the Institute of Seismology conducts research on earth structures using seismic methods. The velocity of seismic waves depends on the properties of the medium, and seismic waves are reflected, refracted and scattered from different interfaces of the subsurface, such as when the rock type changes or from fracture zones. An interpretation of the structures of the subsurface can be formed by registering the ground movement caused by seismic waves with tens, hundreds or even thousands of measuring devices. In seismic reflection soundings, the object of interest is typically the interface between bedrock layers, while in refraction sounding and tomography studies, information is obtained about the composition of the bedrock.
In the following blogs, different researchers will take a closer look at interesting seismological themes and talk about, for example, earthquakes related to postglacial faults, the history and operating principle of seismographs, environmental seismology, the International Nuclear Test Ban Treaty, seismicity in Finland and historically significant earthquakes. So, stay tuned!
Suvi Heinonen, director
