Intraplate earthquakes in Scandinavia and Greenland, Neotectonics or postglacial uplift

Søren Gregersen

Publikation: Bidrag til tidsskriftArtikelForskningpeer review

Abstrakt

Even if the intraplate areas of Scandinavia and Greenland have only experienced small earthquakes
within the time of human tale, we can learn 4 lessons from these regions.

In a small part of Scandinavia, where the present earthquake activity is not significantly different from its surroundings, large faults have been discovered. And these are interpreted to show the occurrence of large earthquakes about 10,000 years ago. Signs of this are coincident landslides as well as liquefaction in loose sediments, which are well dated through varve-counting. Many Scandinavian scientists interpret the cause to be the deglaciation after the last Ice Age. And
since the present dominating stress field in the area follows the pattern of the World Stress Map Project, namely compression within the plate, oriented in the direction of the absolute plate motion, the glacier off-loading is a significantly different cause, 10,000 years ago. Stress reorientation clearly indicates that present-day earthquake activity is caused by neotectonics - plate motion.

Into this argument goes the observation from Greenland and Antarctica, that no earthquakes occur under the ice caps. For Scandinavia the argument is that no earthquakes occurred under the ice sheet of the Ice Age, and that the stored stresses were released, when the ice sheet melted 10,000 years ago. A third lesson comes from Greenland. Here we find that the compressional regime in the intraplate region is not reached until several hundreds of kilometers from the mid-ocean ridge. The few existing focal mechanisms show spreading and strike slip motion. This is supported by data from Iceland far out from the spreading zone. When a map became available a few years back of deep-reaching faults in the Denmark a comparison was attempted. The question asked
was, whether we can now point to some of these faults and call them active? Can the regional earthquake distribution be well correlated with the mapped deep faults? And the answer was for part of the region YES; while for another it was NO. The earthquake activity adds its own component to the fault map of Denmark.

The region is full of faults. Can we feel rather safe, because the stress seems to have diminished
since the end of the Ice Age 9,000 years ago? Or can we expect large earthquakes as observed 10,000
years ago?
OriginalsprogEngelsk
Sider (fra-til)25-30
Antal sider6
TidsskriftJournal of Indian Geophysical Union
Vol/bind10
Udgave nummer1
StatusUdgivet - 2006

Programområde

  • Programområde 5: Natur og klima

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