Results

The fracture frequency observed on outcrops of the crystalline rocks is presented in section A and B (Fig. 3), with a logarithmic scale for the fracture frequency because of the large range. In section A, the fracture frequency is generally very high, close to 1000 fractures/m2 over a distance of 1700 m. No transition from high fracture frequency to low is noticed towards the suggested northern margin of the structure. In section B a transition from high to low fracture frequency can be seen. The frequency is variable but high in the northern part of the section, over 1000 fractures

Shattered basement ■ Early Granitoids * Rev sun d «ran it?

Shattered basement ■ Early Granitoids * Rev sun d «ran it?

1DOO 10000 10DGG0 1QOOOGO

Resistivity (Grn)

Fig. 4. Correlation between the fracture frequency and electric resistivity of crystalline rocks in the Lockne impact structure measured in two sections shown in Fig. 1.

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Resistivity (Grn)

Fig. 4. Correlation between the fracture frequency and electric resistivity of crystalline rocks in the Lockne impact structure measured in two sections shown in Fig. 1.

per m2 and thus similar to the frequency in section A. In the transitional part, the fracture frequency declines from ~ 1000 fractures/ m2 to ~10 fractures/m2. This transition occurs within 1100 m, from 500 to 1600 m distance from the start of the section. In the southernmost area of section B, the fracture frequency remains at 10 fractures/m2. At 1000 m in section B there is a step in the fracture frequency over one order of magnitude, shown as a light gray area in Figure 3.

The crystalline rocks have different resistivity values depending on the amount of brecciation. The non-brecciated crystalline rocks have resistivities of >10 000 Om. The brecciated crystalline rocks have resistivities ranging from 10 000 to 300 Om depending on the amount of brecciation.

The correlation between the two-dimensional fracture frequency and resistivity measured on the outcrops along section A and B is shown in Fig. 4.

The correlation plots as a straight line on doubly logarithmic axes, indicating that it has a power law functional form. The equation for the correlation shown in Fig. 4 relating resistivity and fracture frequency in the Lockne structure is:

where F = fracture frequency (fractures/m2) and R = electric resistivity (Dm) and the constants 9.4 and -1.9 are derived from the linear reduction of the correlation.

The correlation is assumed to be linear although the distribution of data indicates two populations with a rather wide gap, as seen in Fig. 5. This is caused by the rapid decline in fracture frequency and increase in resistivity at 1000 m in section B, when moving away from the crater center. The frequency decrease of the resistivity can be seen in the histogram of resistivity values in Fig. 5, where there are no values between 7000-15000 Dm.

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