ARKHANGELSK, June 16. /TASS/. Seismologists found the least stable karst area in the Arkhangelsk Region's Pinezhsky District, the Laverov Federal Research Center for Integrated Arctic Studies (the Russian Academy of Sciences' Urals Branch) told TASS.
The seismic studies were conducted in the district for the first time, the scientific center's press service said.
"Speleologists have pointed to the least stable area of the Pinezhsky karst. This is a segment of about 0.5 square kilometers, which is located in the Kulogorskaya - Troya cave system between caves K-4 and K-13. The Laverov Center's scientific group used an interdisciplinary approach where they combined seismic, GPR and passive seismic methods. By using this approach they could detail the structure of craters (sinkholes and caves) and karst processes," the press service said.
In March, seismic equipment was installed for the first time in one of the Pinezhye caves - to monitor the mobility of karst - unstable rocks eroded by waters. This time, the scientists faced the task to study in detail the structure of karst caves in the Pinezhsky District.
"The karst occupies about a quarter of the Arkhangelsk Region. Its huge area, for example, is between the Onega River and the Northern Dvina. Karst caves are unstable, developing, "living" structures. Sinkholes and landslides are developing permanently in the district. Seismic exploration is a most effective geophysical method to study in detail the structure of the Earth's crust upper part. In our case, this is engineering, shallow-depth seismic exploration, by using which we can "look" down up to 100 meters," the center's expert, Corresponding Member of the Russian Academy of Sciences Galina Antonovskaya said.
Karst carbonate rocks lie at depths up to 120 meters. According to expert Irina Basakina, GPR studies, which effectively obtain information about geological environment, do not always provide a complete "underground picture." Clay deposits would reflect the wave not allowing researchers to look deeper. Therefore, geophysicists use different techniques and compare obtained results. During shallow-depth seismic exploration, scientists use a sledgehammer to launch artificially shock waves deep into the earth and then they use special sensors to record how the waves run inside rocks.
Rocks' structures under the karst
The researchers have used also so-called passive seismic methods to see the rock structure at depths below the karst.
"By using the temporary monitoring system that we install beforehand, we record the seismic activity associated with cave destruction. Seismic exploration identifies formation of new craters, as well as fracturing that specifies the rock structure. We use passive seismic methods to identify how much "alive" a particular fracture zone is, how it is developing, whether it is active or passive right now. In other words, we expand view by observing the karst, and we can identify potentially dangerous areas," Antonovskaya added.
This research is important, among other aspects, for the safety of local residents, whose homes may be in close proximity to the intensively developing karst.