Tectonic stress in the Earth's crust: advances in the World Stress Map project B. SPERNER 1 , B. MULLER!, O. HEIDBACH l , D. DELVAUX 2 ,3, J. REINECKER 1 & K. FUCHS l 'Oeophysical Institute, Karlsruhe University, Hertzstrasse 16, 76187 Karlsruhe, Germany (e-mail: blanka.sperner@gpi.uni-karlsruhe.de) 2Royal Museum for Central Africa, Leuvensesteeweg 13, 3080 Tervuren, Belgium 3Present address: Vrije University, Amsterdam, The Netherlands Abstract: Tectonic stress is one of the fundamental data sets in Earth sciences comparable with topography, gravity, heat flow and others. The importance of stress observations for both aca- demic research (e.g. geodynamics, plate tectonics) and applied sciences (e.g. hydrocarbon pro- duction, civil engineering) proves the necessity of a project like the World Stress Map for com- piling and making available stress data on a global scale. The World Stress Map project offers not only free access to this global database via the Internet, but also continues in its effort to expand and improve the database, to develop new quality criteria, and to initiate topical research projects. In this paper we present (a) the new release of the World Stress Map, (b) expanded quality ranking schemes for borehole breakouts and geological indicators, (c) new stress indi- cators (drilling-induced fractures, borehole slotter data) and their quality ranking schemes, and (d) examples for the application of tectonic stress data. Tectonic stress is felt most extremely during its release in catastrophic earthquakes, although less spectacular tectonic stress is a key safety factor for underground constructions such as tunnels, caverns for gas storage or deposits of nuclear waste (Fuchs & Muller 2001). Furthermore, the economic aspect is of increasing importance in hydrocarbon recovery. Knowledge of the stress field is used in the hydrocarbon industry to foresee stability prob- lems of boreholes and to optimize reservoir man- agement through tectonic modelling in combi- nation with correlation with other data sets such as 3D-structural information, e.g. location and orien- tation of faults. Geodetic measurements (e.g. Global Positioning System, GPS; Very Long Baseline Interferometry, VLBI; Satellite Laser Ranging, SLR) have become available in increasing numbers and enhanced quality. They provide surface displacement vectors from which the strain rate field can be deduced. The combined interpretation of stress and strain rate data provides unique challenges for Earth scientists in a number of fields. In tectonics, plate boundary forces confine the kinematics of plate motion and the dynamics of plate deformation resulting, for example, in major differences between intraplate and plate boundary deformation zones. The width of the latter even varies for the different types of plate boundaries (Gordon & Stein 1992). These differences express the laterally and vertically heterogeneous deformation pattern of the crust due to its composition, mechanical properties and tectonic setting. The comparison of the strain rate field at the surface with earthquake data from the seismogenic part of the crust will give infor- mation on the depth variation of strain. The relationship of strain and stress is of special impor- tance at active fault zones, where accumulated stress is abruptly released in earthquakes. The scale of stress impact ranges from a continent-wide scale in order to explain tectonic processes, to a metre scale at reservoir and con- struction sites. The global database World Stress Map (WSM) provides information on the contem- porary tectonic stress in the Earth's crust in a com- pact and comprehensive way. The WSM project was initiated as a task force of the International Lithosphere Program under the leadership of M. L. Zoback. The database is now maintained and expanded at the Geophysical Institute of Karlsruhe University as a research project of the Heidelberg Academy of Sciences and Humanities. The WSM team regards itself as 'brokers' for these fundamen- tal data: data of different types from all over the world are integrated into a compact database fol- lowing standardized procedures for quality assign- From: NIEUWLAND, D.A. (ed.) New Insights into Structural Interpretation and Modelling. Geological Society, London, Special Publications, 212, 101-116. 0305-8719/03/$15 © The Geological Society of London 2003.