Topography and its isostatic compensation as a cause of seismicity of the apennines

Abstract

The load generated by the Apennines and its isostatic adjustment is simulated on an elastic spherical model, and an estimate made of the maximum shear stress field produced. For this purpose a load on a shell with isostatic compensation is considered showing that the couple effect associated with the displacement of the compensation greatly increases the maximum shear stress as compared with the case of no displacement. When the results of the present study are compared with those obtained from seismicity and from the gravity anomalies of the Apennines, it is found that the largest earthquakes in the region and its most seismically active part are in the area of the largest shear stress and of large gravity anomaly gradient. A pattern recognition study of the correlation between large earthquakes and gravity anomalies (Benvenuti and Caputo, 1982) confirms this result. The case of a load on a spherical cap not isostatically compensated is also considered; the finding in this case are in agreement with Jeffrey's (1976) results for a half space, although in our case the largest value of the maximum shear stress occurs at a shallower depth. This case is of interest for those continents where the isostatic compensation is not complete.