Использование соотношения между интенсивностью и Балльностью) землетрясений для оценки глуБины астеносферы в районе вранча (карпаты)

Summary

The correlation between the magnitudeM and intensityI of an earthquake is found [4]: 1·5M−I=δ(h), where δ(h) is a simple function of focal depthh:

$$\begin{gathered} \delta (h) = - 3 \cdot 0 + 3 \cdot 5\lg h, 0< h< 60 - 100 km, \hfill \\ \delta (h) = - 5 \cdot 4 + 3 \cdot 5\lg h, 60 - 100 km< h< 640 km. \hfill \\ \end{gathered} $$

Thus at a depth of 60–100 km the value of δ(h) changes with a jump from 3·2–4·0 to 0·9–1·5 (Fig. 1). This may be explained by the decrease in the long wave amplitudes on the Earth’s surface due to the upper boundary of the asthenosphere reflecting seismic rays from underlying foci.

It is found that the sudden decreasing of δ(h) for all the earthquakes of some definite region takes place at a definite depth. For the Carpathian earthquakes this depth is found to be 100 km (Fig. 2). Some typical records for the foci lying under and over the upper boundary of the asthenosphere are shown (Fig. 3).