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The Warsaw Voice » Society » March 31, 2015
Institute of Geophysics Polish Academy of Science
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Peering Deep Under the Earth’s Crust
March 31, 2015   
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Researchers from the Department of Lithospheric Research, part of the Polish Academy of Sciences’ Institute of Geophysics, can be regarded as historians specializing in the evolution of the Earth; seismic phenomena in the planet’s lithosphere speak volumes about the past 3.5 billion years.

The lithosphere, the outer layer of the Earth, comprises the crust and upper mantle. This is where all available mineral resources are located. Research into what lies deep under the surface of the Earth allows scientists to determine the structure and physical state of the planet and understand how it has evolved. Such studies are based on geophysical research, especially on methods that analyze the propagation of seismic waves generated in the Earth’s crust by natural earthquakes and manmade vibrations such as explosions.

The Department of Lithospheric Research uses active seismic methods that penetrate the lithosphere up to a depth of 100 kilometers. The most important body of research concerns crust that is 30-40 km thick on continents and a dozen or so kilometers under the oceans. The researchers are mostly interested in Central Europe, as the area between the Baltic, Adriatic and Black Seas has an extremely complicated geological structure and tectonic history. Geological maps of this part of Europe show that Poland has the most complex mix of geological structures in the region. Northeastern Poland sits on the Eastern European craton—an old and stable part of the continental lithosphere—which is up to 3.5 billion years old, while the west of the country is formed by the tip of the paleozoic platform of Central and Western Europe, which is 300-400 million years old. Pushing in from the south is the Alpideorogenic (mountain-forming) belt, whose Polish section is part of the Carpathian mountains. These three immense tectonic formations converge in southeastern Poland, making the region a crucial source of information on geodynamic processes that have taken place in Europe. In order to understand these processes, the Department of Lithospheric Research has for many years worked closely with partners in Western and Southern Europe as well as in Ukraine and Belarus. Their joint efforts include a host of large-scale active seismic experiments. These have employed state-of-the-art seismic stations brought in from many European countries, the United States and Canada. In recent years, much of this research has been focused on Ukraine.

After 2007, a lot of research projects were carried out on six fault lines, aiming to identify the structure of the ridge of the Eastern European craton and the Southeastern European extension of the Teisseyre-Tornquist fault zone that cuts through Poland. Prof. Tomasz Janik, who heads the Department of Lithospheric Research, says his team led all these projects. “This was because of our experience and know-how in preparing experiments and then gathering and interpreting data,” says Janik. “We are one of the world’s leading research centers.”

Problems that geophysicists encounter in their work are often of a completely non-scientific nature. Prof. Aleksander Guterch, who has worked at the Department of Lithospheric Research the longest and who used to head the department, says that national borders constitute a major hindrance to geodynamic studies. “Coping with regulations and restrictions is nothing short of a nightmare, as is trying to obtain permission for specific research projects,” says Guterch. “Americans are surprised to see that despite so many political borders, geodynamic research is nevertheless conducted in Europe.” It was not until European integration happened that a radical change took place and expensive seismic equipment could finally be shipped across borders without complications.

Active seismic research uses seismic waves set off by explosions. Explosive charges used in such experiments range from several hundred kilograms of TNT to over a metric ton. “I started such experiments in Poland in the late 1960s,” says Guterch. After communism fell, researchers from the Department of Lithospheric Research initiated four major international seismic experiments in Central and Southern Europe. The projects were called Polonaise ’97, Celebration 2000, ALP 2002, and Sudetes 2003, and were carried out in 1997-2003. New-generation seismic data obtained from the experiments will be used by researchers for many years to come. Some of the data is so complicated that the Department of Lithospheric Research is still working to interpret it. So far, findings from the experiments have been cited in around 100 publications, including international science magazines and prestigious monographs. The four research projects were carried out as a joint international effort by 35 research and industry organizations from 17 European countries, the United States and Canada. The experiments were conducted on seismic profiles with a total length of over 20,000 km.

Celebration 2000 (short for Central European Lithospheric Experiment Based on Refraction) was the largest of the four projects, with experiments conducted in western Russia, Belarus, Poland, Slovakia, the Czech Republic, Austria, Hungary and Germany. Seismic waves were generated at 147 so-called shot points and recorded by 2,340 cutting-edge seismic stations brought from European countries and the United States. It is estimated that at the time of the experiment, the expensive seismic stations used in it accounted for 70 percent of all of the world’s equipment of this kind. In order to prepare the shot points, a huge number of holes were bored in the ground, each around 30 meters deep and packed with 50 kilograms of TNT.

The seismic waves generated by the explosions penetrated up to 100 km into the lithosphere. They were registered along specified profile lines by stations placed every 2 km. This dense array of seismic stations and lines enabled the researchers to record seismic waves from all shot points and coming from different directions. The data obtained was subsequently used to identify the spatial structure of the Earth’s crust in the studied areas.

The Celebration 2000 experiment covered an area of around 500,000 square kilometers and involved around 800 technical staff and several dozen researchers. It lasted 30 days and nights. In a special report, the European Foundation for Science described Celebration 2000 as the largest research project of this kind in the history of world geophysics. The Oxford Guide to Modern Science (2003), a special publication of the University of Oxford, named Celebration 2000 as one of the experiments that brought science into the 21st century.

According to Guterch, technological barriers encountered during research into what is hiding inside the Earth are incomparably harder to overcome than in space exploration. Boreholes reaching just 3-4 km under the Earth’s surface cost around zl.30 million. The deepest holes that the Americans have bored in the Gulf of Mexico reach 12 km inside the crust. “Consequently, geophysical methods are the only efficient way to study the interior of the Earth and seismic methods are the most important of them,” says Guterch.

Active seismic methods employing explosives have also been used in large-scale explorations of the deep structure of the crust in polar regions, the Western Antarctic and the Svalbard Archipelago in the Arctic. In 1976-2010, experts from the Department of Lithospheric Research organized seven expeditions to the Arctic and five to the Antarctic. The areas selected for research in the two regions are of key importance to the geodynamics of the Earth. A large amount of the research was carried out as part of international projects. Before the Polish researchers arrived in the Antarctic, nobody had carried out such a systematic series of experiments and Antarctic research is considered a “Polish specialty” to this day.

In recent years, a new kind of broadband seafloor seismic station has been introduced. These devices can stay submerged up to 6 km underwater for around one year. After they are recovered, data analysis begins, presenting new opportunities for researchers in polar regions. Economic issues have recently boosted the importance of seismic research in these areas. Guterch says that crude oil deposits in the Arctic are estimated at around 20 percent of total global resources and deposits of natural gas at 30 percent.

Highlighting how important scientific research has become to industry and the economy, the researchers from Department of Lithospheric Research work closely with Poland’s Environment Ministry and Polish natural gas giant PGNiG. “We have been persuading young oil industry experts that in order to make progress in the search for energy resources these days, you need to precisely identify the deep structure of the Earth’s crust,” says Guterch.
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