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Workreport 1997-61

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Name:

Olkiluodon alueen seismisyys

Writer:

Jouni Saari

Language:

Finnish

Page count:

44

Summary:

Working report: Saari J., 1997. Seismicity in the Olkiluoto area. Posiva Oy, Work Report-97-61,
38 pages


ABSTRACT

Posiva Oy studies the bedrock of the island of Olkiluoto in Eurajoki for the final
disposal of the spent fuel from the Finnish nuclear power plants. The study deals
with the seismicity of the Olkiluoto area in relation to the general seismicity of the
Fennoscandian Shield and the region of the southwestern Finland.

The study covers an area within 500 km from Olkiluoto. The area includes
altogether over 900 observations of earthquakes since 1375. About 1/3 of those
has been observed by seismic instruments during the years 1965 - 1995.

The distribution of the seismicity in the southwestern Finland and in the Bothnian
Sea area is presented in a geological map. The study shows that the Saaristomeri-
Paldis-Pskov Seismic Zone has an important role when the seismicity in southern
Finland and in Estonia is concerned. All significant earthquakes (M is greater or equal
to 3.5) in the
region of the Gulf of Finland and in the Ålands archipelago are related to this
zone.

The 1976 Osmussaar earthquake, in the northwestern coast of Estonia, was felt
also in Eurajoki. This event was exceptionally strong (mb = 4.7) in the area. The
event is often associated with the proposed fault zone running diagonally through
the Gulf of Finland in the direction of WSW-ENE. The Osmussaar event is
reviewed on the basis of current geological and seismological knowledge.

Within a radius of 100 km from Eurajoki there has been altogether 6 earthquakes.
The nearest event (M = 3.1) occurred 1926 in Uusikaupunki, 35 - 40 km from
Olkiluoto, as a part of the active period in the Saaristomeri-Paldis-Pskov Zone.
The earthquakes of the area are small (M is less or equal to 3.1)
and their recurrent periods are
long. This means that the potential impact on the vault due to of seismicity are
likely indirect changes in the surrounding bedrock structure, stress field and
groundwater conditions.

In addition to the seismic zoning, the aim of the seismotectonic interpretation was
to identify individual active shear or thrust zones. Two nearest active zones from
Olkiluoto seem to be NW-SE oriented. The southern one of those runs along the
contact of the Laitila rapakivi massif, about 20 km SW from Olkiluoto. The other
one runs along the edge of the Satakunta sandstone formation, about 35 km NE
from Olkiluoto. These potentially active zones are possibly related to 1 - 2 small
(M = 2.7 - 3.1) earthquakes.
Saari J., 1997. Seismicity in the Olkiluoto area. Posiva Oy, Work Report-97-61,
38 pages


ABSTRACT

Posiva Oy studies the bedrock of the island of Olkiluoto in Eurajoki for the final
disposal of the spent fuel from the Finnish nuclear power plants. The study deals
with the seismicity of the Olkiluoto area in relation to the general seismicity of the
Fennoscandian Shield and the region of the southwestern Finland.

The study covers an area within 500 km from Olkiluoto. The area includes
altogether over 900 observations of earthquakes since 1375. About 1/3 of those
has been observed by seismic instruments during the years 1965 - 1995.

The distribution of the seismicity in the southwestern Finland and in the Bothnian
Sea area is presented in a geological map. The study shows that the Saaristomeri-
Paldis-Pskov Seismic Zone has an important role when the seismicity in southern
Finland and in Estonia is concerned. All significant earthquakes (M is greater or equal
to 3.5) in the
region of the Gulf of Finland and in the Ålands archipelago are related to this
zone.

The 1976 Osmussaar earthquake, in the northwestern coast of Estonia, was felt
also in Eurajoki. This event was exceptionally strong (mb = 4.7) in the area. The
event is often associated with the proposed fault zone running diagonally through
the Gulf of Finland in the direction of WSW-ENE. The Osmussaar event is
reviewed on the basis of current geological and seismological knowledge.

Within a radius of 100 km from Eurajoki there has been altogether 6 earthquakes.
The nearest event (M = 3.1) occurred 1926 in Uusikaupunki, 35 - 40 km from
Olkiluoto, as a part of the active period in the Saaristomeri-Paldis-Pskov Zone.
The earthquakes of the area are small (M is less or equal to 3.1)
and their recurrent periods are
long. This means that the potential impact on the vault due to of seismicity are
likely indirect changes in the surrounding bedrock structure, stress field and
groundwater conditions.

In addition to the seismic zoning, the aim of the seismotectonic interpretation was
to identify individual active shear or thrust zones. Two nearest active zones from
Olkiluoto seem to be NW-SE oriented. The southern one of those runs along the
contact of the Laitila rapakivi massif, about 20 km SW from Olkiluoto. The other
one runs along the edge of the Satakunta sandstone formation, about 35 km NE
from Olkiluoto. These potentially active zones are possibly related to 1 - 2 small
(M = 2.7 - 3.1) earthquakes.

Keywords:

File(s):

Olkiluodon alueen seismisyys (pdf) (2.1 MB)


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