murroslinjavaaitus km - - Geologian tutkimuskeskus

murroslinjavaaitus km - - Geologian tutkimuskeskus

Aarne Verio, Aimo Kuivamaki and Paavo Vuorela, 1993. Recent displace-

ments within reactivated fracture systems in Finland; results and

analysis of levelling measurements carried out by the National Land

Survey of Finland between 1974-1992. Geological Survey of Finland,

Nuclear Waste Disposal Research, report YST-84. Part 1: text, 189

pages, 98 figures and 61 tables; Part II: 3 pages and 44 appendices.

A block mosaic model of the bedrock of the Fennoscandian shield, as

well observations of potential displacements associated with existing

f racture zones, have been used in determining the most suitable sites

for radioactive waste disposal in Finland. It is considered likely

that movements related to isostatic readjustments following future

deglaciations will take place preferentially along the same zones

that are accommodating slow uplift at present.

Estimations of the distribution and intensity of bedrock movements

in the recent past have been made on the basis of observations from

faults, fault scarps and land slides and associated deposits within

and affecting Quaternary sediments.

In 1974 Aarne Veriö commenced a program of remeasuring the old

levelling network of the National Land Survey, in order to ascertain

the location and magnitude of present day irregularities in uplift

rate. This study revealed that instead of uniform plastic rebound,

bedrock movements appear to be concentrated within discrete fracture

zones separating more inert blocks. A series of new levelling

profiles were constructed across such fracture zones, and the number

of bench marks on selected old profiles was also increased. During

the early stages of investigation, potential movement zones were

identified using relatively generalized and small scale maps. Since

the early 1970fs, the National Land Survey of Finland has been

responsible for subsequent measurement of the newer levelling

prof iles.

This report presents results for a total of 53 levelling profiles,

with a combined length of 1300 km, carried out by the National Land

Survey between 1974 and 1992. The profiles were selected by the

National Land Survey and represent measurements over intervals

ranging from 4 to 81 years, with a mean of 23 years. Seventeen

profiles have been measured on at least three occasions, which has

permitted the continuity and directions and magnitudes of displace-

ments to be evaluated.

The report also contains background information and additional data,

measured during one levelling survey, from the Lavia, Kivetty and

Pasmajarvi sites.

Of the 53 profiles presented here, 27 recorded significant local

changes in elevation, while a further 7 showed variations that

deviate substantially from predictions based on uniform elastic

uplift. The 19 rernaining profiles either did not show any evidence

of movement, or else displacements took place in accord with tilting

estimates based on uniform uplift rates. Magnitudes of uplift rate,

classified as significant to highly significant, varied from 0.24

mrn/year to 1.52 mmlyear, with the highest individual cumulative

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