Geologically extremely rapid changes in attitude by glacial rebound of the Earth crust after retreat of the Scandinavian Ice Sheet at the end of the last Weichsetian glaciation influenced the patae- ogeography of nort...Geologically extremely rapid changes in attitude by glacial rebound of the Earth crust after retreat of the Scandinavian Ice Sheet at the end of the last Weichsetian glaciation influenced the patae- ogeography of northern Europe. The up（ift of the Earth crust apparently was not gradual, but shock-wise, as the uplift was accompanied by frequent, high-magnitude earthquakes. This can be deduced from strongly deformed layers which are interpreted as seismites. Such seismites have been described from several coun- tries around the Baltic Sea, including Sweden, Germany and Poland. Now similarly deformed layers that must also be interpreted as seismites, have been discovered also in Latvia, a Baltic country that was covered by an ice sheet during the last glaciation. The seismites were found at two sites： Near Vatmiera in the NE part and near Rakuti in the SE part of the country. The seismites were found in sections of about 7 m and 4.5 m high, respectively, that consist mainly of glaciofluvial and gtaciotacustrine sands and silts. At the Vatmiera site, 7 seismites were found, and at the Rakuti site these were even 12 seismites. The two sections have not been dated precisely up tilt now, but lithological correlations and geomorpho- logical characteristics suggest that the sediments at the Vatmiera site cannot be older than 14.5 ka. Because the accumulation of the section did not take more than about 1000 years, the average recurrence time of the high-magnitude （M≥4.5-5.0） earthquakes must have been maximally only 100-150 years, possibly only 6-7 years. The sediments at Rakuti must also have formed within approx. 1000 years （17-16 ka）, implying a recurrence time of high-magnitude earthquakes of maximaUy once per 100-200 years.展开更多
基金financially supported by grants from the National Science Centre Poland(based on decisions No.DEC-2013/09/B/ST10/00031 and No 2015/19/B/ST10/00661)
文摘Geologically extremely rapid changes in attitude by glacial rebound of the Earth crust after retreat of the Scandinavian Ice Sheet at the end of the last Weichsetian glaciation influenced the patae- ogeography of northern Europe. The up（ift of the Earth crust apparently was not gradual, but shock-wise, as the uplift was accompanied by frequent, high-magnitude earthquakes. This can be deduced from strongly deformed layers which are interpreted as seismites. Such seismites have been described from several coun- tries around the Baltic Sea, including Sweden, Germany and Poland. Now similarly deformed layers that must also be interpreted as seismites, have been discovered also in Latvia, a Baltic country that was covered by an ice sheet during the last glaciation. The seismites were found at two sites： Near Vatmiera in the NE part and near Rakuti in the SE part of the country. The seismites were found in sections of about 7 m and 4.5 m high, respectively, that consist mainly of glaciofluvial and gtaciotacustrine sands and silts. At the Vatmiera site, 7 seismites were found, and at the Rakuti site these were even 12 seismites. The two sections have not been dated precisely up tilt now, but lithological correlations and geomorpho- logical characteristics suggest that the sediments at the Vatmiera site cannot be older than 14.5 ka. Because the accumulation of the section did not take more than about 1000 years, the average recurrence time of the high-magnitude （M≥4.5-5.0） earthquakes must have been maximally only 100-150 years, possibly only 6-7 years. The sediments at Rakuti must also have formed within approx. 1000 years （17-16 ka）, implying a recurrence time of high-magnitude earthquakes of maximaUy once per 100-200 years.
