John Reinecker

Tectonic stress in the Earth’s crust: advances in the World Stress Map project

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 academic research (e.g. geodynamics, plate tectonics) and applied sciences (e.g. hydrocarbon production, civil engineering) proves the necessity of a project like the World Stress Map for compiling 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 indicators (drilling-induced fractures, borehole slotter data) and their quality ranking schemes, and (d) examples for the application of tectonic stress data.

Understanding tectonic stress in the oil patch The World Stress Map Project

Knowledge of the present-day tectonic stress is essential for numerous applications in petroleum exploration and production and in civil and mining engineering, such as improving the stability of boreholes and tunnels and enhancing petroleum production through natural or induced fractures. The World Stress Map (WSM) Project is a collaborative project between academia, industry, and government that is building a comprehensive global database of present-day stress information to better understand the state and sources of contemporary tectonic stress in the lithosphere (Figure 1).

Thermal history of the central Gotthard and Aar massifs, European Alps: Evidence for steady state, long‐term exhumation

[1] Quantifying long‐term exhumation rates is a prerequisite for understanding the geodynamic evolution of orogens and their exogenic and endogenic driving forces. Here we reconstruct the exhumation history of the central Aar and Gotthard external crystalline massifs in the European Alps using apatite and zircon fission track and apatite (U‐Th)/He data. Age‐elevation relationships and time‐temperature paths derived from thermal history modeling are interpreted to reflect nearly constant exhumation of ∼0.5 km/Ma since ∼14 Ma. A slightly accelerated rate (∼0.7 km/Ma) occurred from 16 to 14 Ma and again from 10 to 7 Ma. Faster exhumation between 16 and 14 Ma is most likely linked to indentation of the Adriatic wedge and related thrusting along the Alpine sole thrust, which, in turn, caused uplift and exhumation in the external crystalline massifs. The data suggest nearly steady, moderate exhumation rates since ∼14 Ma, regardless of major exogenic and endogenic forces such as a change to wetter climate conditions around 5 Ma or orogen‐perpendicular extension initiated in Pliocene times. Recent uplift and denudation rates, interpreted to be the result of climate fluctuations and associated increase in erosional efficiency, are nearly twice this ∼0.5 km/Ma paleoexhumation rate.

Stress maps in a minute: The 2004 world stress map release

The World Stress Map (WSM) project has, since 1986, been compiling a free and public global database of contemporary crustal stress information.The WSM is now a key resource, for scientists and engineers in both academia and industry, that is used for understanding geodynamic processes, seismic hazard assessment, the stability of tunnels, improving hydrocarbon production, safe subsurface disposal of waste and greenhouse gases, and geothermal power production [Fuchs and Muller, 2001]. The WSM 2004 release, issued on 27 May 2004, contains over 13,800 data sets of contemporary crustal stress information, all of which can be downloaded free of charge from the project Web site: http://www. world-stress-map. org. The WSM Web site also includes stress maps, software, stress interpretation guidelines, and the fast online database interface “Create a Stress Map Online” (CASMO). CASMO allows WSM users to create high graphic quality stress maps to their own specifications that are delivered to the user via email within a minute.

What perturbs isotherms? An assessment using fission-track thermochronology and thermal modelling along the Gotthard transect, Central Alps

Abstract Interpretation of low-temperature thermochronological data usually relies on assumptions on the shape of isotherms. Recently, a number of thermal modelling approaches investigate and predict the theoretical influence of topography on isotherms. The application and proof of these predictions is not well confirmed by measured data. Here we present apatite fission-track (AFT) data from samples collected along the Gotthard road tunnel and its corresponding surface line to test these predictions. AFT ages broadly cluster around 6 Ma along the tunnel. No correlation of tunnel ages with superimposed topography is seen, which means that topography-induced perturbation of isotherms under given boundary conditions (topographic wavelength 12 km; relief 1.5 km; exhumation rate 0.45 km Ma−1) can be neglected for the interpretation of AFT ages. Thus, in areas characterized by similar topographies and exhumation rates, apparent exhumation rates deduced from the age–elevation relationship (AER) of AFT data need no correction for topography-induced perturbation of isotherms. Three-dimensional (3D) numerical thermal modelling was carried out incorporating thermally relevant parameters and mechanisms, such as topography, geology, thermal conductivities and heat production. Modelling reveals a strong influence on the shape of isotherms caused by spatially variable thermal parameters, especially heat production rates. Therefore, not only topography has to be considered for interpreting low-temperature thermochronological data, but also other parameters like heat production rates. Supplementary material: 1. Electron microprobe analyses, 2. Topography and model extend, 3. Model parameters are all available online at http://www.geolsoc.org.uk/SUP18380.

World stress map published

The World Stress Map (WSM), published in April 2007 by the Commission for the Geological Map of the World and the Heidelberg Academy of Sciences and Humanities, displays the tectonic regime and the orientation of the contemporary maximum horizontal compressional stress at more than 12,000 locations within the Earths crust. The Mercator projection is a scale of 1:46,000,000. The WSM provides insight into large-scale patterns of stress orientations (i.e., first-order stress patterns due to plate boundary forces and second-order stress patterns due to topography), large lateral density variations, and deglaciation effects. Furthermore, the WSM contains a number of regions with high data resolution that enable users to investigate variations in stress orientations on local scales and to discuss factors controlling third-order stress patterns such as active faults, local inclusions, detachment horizons, and density contrasts. Forces resulting from these geological subsurface structures control the stress field orientations especially when magnitudes of the horizontal stresses are close to each other.