J.-Y. Lee

Paleostress trajectory maps based on the results of local determinations: the “LISSAGE” program

Abstract This paper presents a program to reconstruct maps of paleostress trajectories for a given tectonic event, based on the results of multiple local stress determinations. The compiling process from local field data to regional paleostress database, is summarized. Two methods allow transformation of the local scattered directional data into a 2-D regional distribution of trajectories of principal paleostress axes, including a smoothing process: (1) a linear model uses a bivariate polynomial function to express the distribution of regional stress vectors; (2) a distance-weighting method uses an inverse distance weighting function to determine the paleostress direction for any given point within the calculated area. The smoothness degree of trajectories is controlled by the degree of the polynomial function for the linear model, and by the power value and threshold distance for the distance weighting method. The second method generally provides better results. The effects of local stress deviations (resulting from determination uncertainties or local stress perturbations) also are considered through weighting of local data; such individual weights are quantified with confidence intervals according to the quality of the data. The detailed description of the algorithm enables the users to understand the running routine of the program. The graphic output of the program consists of (1) the gridded map, and (2) the trajectories map corresponding to the smoothed stress/paleostress field. A case study shows how the program works.