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Heidbach, Oliver • Ziegler, Moritz
Abstract: The World Stress Map (WSM) is the global compilation of information on the present-day stress field in the Earth's crust. The current WSM database release 2016 (Heidbach et al., 2016) has 42,870 data records, but the data are unevenly distributed and clustered.To analyse the wave-length of the crustal stress pattern of the orientation of maximum horizontal stress Shmax, we use so-called smoothed stress maps that show the mean SHmax orientation on regular grids. The mean SHmax orientation is estimated with the Matlab® script stress2grid (Ziegler and Heidbach, 2017) which is based on the statistics of bi-polar data. The script provides two different approaches to calculate the mean SHmax orientation on regular grids.The first is using a constant search radius around the grid point and computes the mean SHmax orientation if sufficient data records are within the given fixed search radius. This can result in mean SHmax orientations with a high standard deviation of the individual mean SHmax orientation and it may hide local perturbations. Thus, the mean SHmax orientation is not necessarily reliable for a local stress field analysis.The second approach is using variable search radii and determines the search radius for which the standard deviation of the mean SHmax orientation is below a user-defined threshold. This approach delivers the mean SHmax orientations with a user-defined degree of reliability. It resolves local stress perturbations and is not available in areas with no data or conflicting information that result in a large standard deviation.The search radius starts with 1000 km and is decreased in 100 km steps down to 100 km. Mean SHmax orientation is taken and plotted here for the largest search radius when the standard deviation of the mean SHmax orientation at the individual grid points is smaller than 25°. For the estimation of the mean Shmax we selected the following data: A-C quality data without PBE flag.Furthermore, only data records located on the same tectonic plate as the grid point is used to calculate the mean SHmax orientation. Minimum number of data records within the search radius is n = 5 and data records within a distance of d ≤ 200 km to the nearest plate boundary are not used. Plate boundaries are taken from the global model PB2002 from Bird (2003).Furthermore, a distance and data quality weight is applied; the distance threshold is set to 10% of the search radius. We provide the resulting smoothed stress data for four global grids (0.2°, 0.5°, 1°, and 2° grid spacing) using two fixed search radii (250 and 500 km) and the approach with variable search radii. Details on the format of the data files with the mean SHmax orientation are provided in the 2018-002_readme file.
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