The World Stress Map (WSM) is a global database on the contemporary in-situ stress conditions. It is a collaborative project linking academia and industry that aims to characterize the crustal stress patterns and understand the large-scale stress sources. The WSM was established in 1986 at the International Lithosphere Program under the leadership of Mary-Lou Zoback. From 1995 to 2008 it was a project of the Heidelberg Academy of Sciences and Humanities led by Karl Fuchs and Friedemann Wenzel. Since 2012 the WSM is a member of the ICSU World Data System. All stress information is analyzed and compiled in a standardized format and quality-ranked for reliability and comparability on a global scale. The current WSM database release 2016 contains 42,870 data records within the upper 40 km of the Earth’s crust (Fig. 1).
The information collected within the WSM, has been excessively used throughout the years within the geothermal industry for many different geomechanics-related purposes starting from understanding the local and regional in-situ stress patterns of low- and high-temperature geothermal fields, predicting wellbore stability of deep geothermal wells, helping to optimize stimulation operations for EGS and hydrothermal systems, design drilling targets, and drilling paths as well as many others.
Figure 1: The world stress map (update from 2016) showing the orientation of maximum horizontal stress in the Earth’s crust (Heidbach et al. 2016)
The WSM is an open-access database used by various academic and industrial institutions working in a wide range of Earth science disciplines such as geodynamics, hazard assessment, geothermal as well as hydrocarbon exploitation and engineering. The main operational areas where WSM may be used are:
The WSM compiles information of the present-day crustal stress from a wide range of indicators, which might be grouped into four main categories i.e.:
Another classification of indicators of the contemporary stress field is presented in Fig. 2.
Figure. 2. Technical classification of the different stress indicator (Heidbach O. 2016)
The success of the WSM is based on a standardized quality ranking scheme, making all stress indicators comparable on a global scale. The ranking scheme is based mainly on the number, accuracy, and depth of the measurements. The scheme was introduced in 1989 and refined and extended in 2003 and 2010. Currently, it is widely accepted as the ranking scheme, which guarantees reliability and global comparability of the present-day crustal stress data coming from various types of sources. The current WSM database release 2016 uses the quality ranking scheme from 2008. One of the examples of the quality ranking scheme for estimation orientation of maximum horizontal stress from borehole breakouts (BO) localized from caliper logs is presented in the Tab. 1.
Tab. 1. WSM quality criteria for BO data from caliper logs (WSM, 2016) (s.d. – standard deviation)
This concludes our #GeothermalFactsandStats post on the word stress map. For more posts and other insight, follow us on all the major social media platforms.
Author: Michal Kruszewski