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Relative seismic moment tensor determination for Vrancea intermediate depth earthquakes

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The method of relative seismic moment tensor determination proposed byStrelitz (1980) is extended a) from an interactive time domain analysis to an automated frequency domain procedure, and b) from an analysis of subevents of complex deep-focus earthquakes to the study of individual source mechanism of small events recorded at few stations.

The method was applied to the recovery of seismic moment tensor components of 95 intermediate depth earthquakes withM L=2.6–4.9 from the Vrancea region, Romania. The main feature of the obtained fault plane solutions is the horizontality ofP axes and the nonhorizontal orienaation ofT axes (inverse faulting). Those events with high fracture energy per unit area of the fault can be grouped unambiguously into three depth intervals: 102–106 km, 124–135 km and 141–152 km. Moreover, their fault plane solutions are similar to ones of all strong and most moderate events from this region and the last two damaging earthquakes (November 10, 1940 withM W=7.8 and March 4 1977 withM W=7.5) occurred within the third and first depth interval, respectively. This suggests a possible correlation at these depths between fresh fracture of rocks and the occurrence of strong earthquakes.

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Oncescu, M.C. Relative seismic moment tensor determination for Vrancea intermediate depth earthquakes. PAGEOPH 124, 931–940 (1986).

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Key words

  • Seismic moment tensor
  • Vrancea region