The magma could rise from the upper mantle to the middle and upper crust, below the Laacher See (Rhineland-Palatinate) volcano. This is the result of a study carried out by the German Southwest Seismic Service (Erdbebendienst Südwest), together with the German Center for Geoscience Research of the GFZ, Karlsruhe Institute of Technology (KIT) and the Seismological Survey of North Rhine-Westphalia. For the first time, scientists present evidence of deep, low-frequency earthquakes caused by magma movements under the Laacher See volcano. However, there are currently no signs of any volcanic activity in the near future. Researchers report their findings International Geophysical Review.
"The detected earthquakes are generated at great depths and are characterized by unusually low frequencies. Its magnitudes are below the limit of human perception, "explains Professor Joachim Ritter of the Geophysical Institute (GPI) of the KIT. Scientists speak of "low frequency deep" (DLF) earthquakes. They are generated in depths between ten and over forty kilometers, that is, in the earth's crust and in the upper mantle. Its dominant oscillation frequencies are between one and ten Hertz, which is significantly smaller than comparable magnitude tectonic earthquakes.
"DLF earthquakes are considered worldwide as an indication of the movement of magmatic fluids at great depths," explains Professor Torsten Dahm, head of the GFZ earthquake and volcano physics section. "These earthquakes can be observed regularly under active volcanoes, for example in Iceland, Japan or Kamchatka." The results of the study in the East Eifel region suggest that magmatic fluids from the upper mantle of Earth may rise in the earth's crust under the soil. Laacher sees the volcano. This can be interpreted as an indication of the existence and slow recharge of the magma chambers in the crust below the volcano.
In their study, scientists from KIT, GFZ, Erdbebendienst Südwest – the joint seismological services of Rhineland-Palatinate and Baden-Württemberg – and the Seismological Service of North Rhine-Westphalia determined that these earthquakes occur episodically in groups that are narrowly time and space and line along a line between 10 and 45 kilometers deep Scientists concluded that fluids and magmas, ie molten rock, could rise from the upper mantle to the middle and upper crust of the earth below the Laacher volcano See.
"Due to extensive improvements in seismic monitoring networks in the Rhineland-Palatinate and adjacent regions, low-frequency earthquakes could be registered under the Laacher See Volcano for the first time in 2013," says Dr. Martin Hensch, head of the study. in the Erdbebendienst Südwest. "Over the past five years, a total of four spatially well-defined clusters of these DLF earthquakes have been detected in the East Eifel region." The clusters line up along a south-east dipping line of approximately 80 ° south of the Laacher See volcano. In addition to spatial separation, the temporal occurrence of DLF earthquakes is also quite limited: to date, specialists have observed eight episodes of DLF earthquakes lasting between 40 seconds and eight minutes.
However, researchers do not interpret the observed DLF earthquakes as an immediate precursor to any volcanic activity in the near future. "The rise of magma in the surface crust is usually accompanied by swarms of high-frequency earthquakes. This activity has not yet been observed in Eastern Eifel, "reports Joachim Ritter. "In addition, there is no sign of deformation on the surface of the Earth, which must be clearly detectable during the huge magma ascents," adds Torsten Dahm. The dating of the magma produced during the last eruption 12,900 years ago shows that the filling and differentiation of the upper magma chamber under the Laacher See Volcano could have taken about 30,000 years before the actual eruption occurred. This means that magmatic processes take a long time before an eruption occurs. As the technical requirements for the detection and location of DLF earthquakes in the East Eifel region have reached only a sufficient quality in recent years, it is not possible to determine retrospectively since when DLF earthquakes occurred in the region. It can be assumed that this was already happening before 2013. After the first observation of deep earthquakes in 2013, KIT, GFZ and Erdbebendienst Südwest installed a seismological research network. The joint use of seismic records now allows detailed scientific analysis of micro-nature.
In order to better investigate the interrelationship between DLF earthquakes and possible magmatic activities under the East Eifel region, the researchers recommend intensifying geochemical monitoring to analyze the emitted gases as well as repeated geodetic measurements to detect possible deformations on the Earth's surface. Specific geophysical investigations must also be carried out to map and characterize possible magma reservoirs under the Laacher See Volcano. In addition, scientists advise a re-evaluation of the volcanic hazard of Eifel.
GFZ GeoForschungsZentrum Potsdam, Helmholtz Center. .