地殻応力場に及ぼす地形の影響 (I)

抄録

Recently, in situ stress measurements have been carried out in Japan by various methods. Measured stresses, however, are apt to be different from regional tectonic stress field, because of such disturbing factors as topography, geological structure, material properties of rocks, and so on. Since the measurements are made at merely shallow sites, topographic effects on tectonic stress field are expected to be larger than other factors. Especially in mountainous area, they may become considerable.
In order to estimate topographic effects, a three-dimensional finite-element analysis is applied to some simple models, which represent mountainous area, on the assumption of homogeneous elastic properties. Furthermore, to geographically realistic models around measuring sites, the same analysis is applied.
The results show that (1) at relatively shallow points, stresses affected by topography are generally different from regional stress acting around the model, (2) therefore, measured stress obtained at shallow sites should be put in a topographic correction, but that (3) such topographic effects become negligible beneath the depth comparable to an amplitude of topographic undulation.