Abstract
The world-wide strain release in relation to focal depth has been calculated for all shocks with magnitude 7 and over for the interval 1918–1952. The strain exhibits a strong maximum in the uppermost 75 km of the earth; it decreases exponentially with depth between 75 and 400 km, with an unimportant minimum corresponding to the asthenosphere low-velocity layer and another minimum at 275 km; after a pronounced minimum between 400 and 475 km it increases again approximately exponentially between 475 and 650 km, after which it drops rapidly to zero. The shape of the strain-depth curve is interpreted in terms of the physical conditions and the intensity of strain accumulation. In particular, the increase between 475 and 650 km is ascribed to a combined effect of temperature and pressure variation with depth with related phase changes and possible changes in composition. The depth curve for the number of shocks is nearly parallel to the strain-depth curve, and the average strain per earthquake shows only an insignificant decrease with depth.
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