Finite element analysis of strain patterns from geodetic observations across a plate margin

Abstract

Abstract Repeated trilateration measurements of local or regional networks are frequently the basis of geodetic strain analyses. As a rule, the strain field is considered homogeneous for the whole area under investigation or at least for parts of it. However, the treatment of strain as homogeneous over a large area means averaging strains and is often not desired. To get an insight into the local variety of strain patterns, the area under investigation can be dissected into finite elements i.e. triangles. The individual analyses of these elements lead to meaningful results which can serve as a basis for refined models of interpretation. Emphasis is put on a strict analysis considering all correlations rigorously. This concerns: 1. (1) point displacements and their variance-covariance matrix as derived from the original geodetic observations through network adjustments. 2. (2) distortions of observables, i.e. distances and angles as derived from the point displacements, and their variance-covariance matrix. 3. (3) global, regional and local strain parameters and their variance-covariance matrix as derived from point displacements or from distorted observables. The method of strain analysis using finite elements is illustrated by a network spanning the San Andreas and Calaveras faults near Hollister, California.