3D finite-element model of the absolute stress state of the Marmara Sea region
(Tobias Hergert, Oliver Heidbach, Anne Becel, Alfred Hirn)
The 1999 Izmit earthquake is supposed to be a precursor of an expected future earthquake beneath the Sea of Marmara
about 20 km south of the city of Istanbul. During the last decade earthquake hazard in this region has been investigated
by several approaches based on Coulomb failure stress changes, earthquake recurrence rates, geodetic analyses, seismic
moment-frequency relationships, and others. In our work build a structurally complex 3D numerical model that simulates
the absolute 3D stress field. The model geometry includes the 3D fault system with Coulomb friction, topography, bathymetry,
water load, basement, and Moho structure. The model is driven by gravity and kinematic boundary conditions. Our results
indicate that slip-rates along the main fault in the Marmara Sea vary significantly along strike and that they are smaller
(12-18 mm/a) than previously anticipated from existing GPS data analysis (19-27 mm/a). The modelled tectonic regime is
consistent with earthquake focal mechanism solutions. Furthermore, it shows that, even though strike-slip regime prevails,
at a number of sites normal faulting occurs.
Spatio-temporal evolution of pore-pressure stress coupling
(Birgit Müller, Martin Schönball, Johannes Altmann, Anna Dorner, Oliver Heidbach)
Geomechanical modelling of a reservoir is important to understand the coupling between pore pressure and stress
state in a reservoir. Changes of pore pressure due to injection or depletion implies also a spatio-temporal
re-distribution of the stress state. Reservoirs are complex underground storage volumes in which the role of pore
pressure stress coupling is not fully understood. To quantify the spatio-temporal evolution of pore pressure
stress coupling in complex settings we solve the coupled differential equations of quasi-static poroelasticity
with the 3D finite element method. Our modelling results indicate that in the early stage of fluid injection
experiments pore pressure stress coupling deviates significantly from a description in the static limit.
Global crustal stress pattern from statistical analysis
(Oliver Heidbach, Mark Tingay, Birgit Müller, Daniel Kurfeß, John Reinecker)
We reinvestigate the global stress pattern by means of a statistical analysis using the Mardia statistics.
In contrast to earlier studies we accomplish a global spatial wave-length analysis of the mean SH orientation on a 0.5° grid.
The resulting hybrid smoothed global stress map displays both the mean SH orientation that results from the maximum smoothing
radius for which the standard deviation is < 25° and the maximum smoothing radius. This hybrid global map confirms that
long spatial wave-length stress patterns (>2000 km) exist in some areas (e.g. North America, NE Asia). Such long spatial
wave-length stress patterns have been used in earlier analyses to conclude that the global stress pattern is primarily
controlled by plate boundary forces that are transmitted throughout the intraplate region. However, our analysis also reveals
that shorter spatial wave-length variations in the stress pattern, in the order of less than 200 km, are very common,
particularly in western Europe, Alaska and the Aleutians, the southern Rocky Mountains, Basin and Range province, Scandinavia,
Caucasus, most of the Himalayas and Indonesia. This implies that local stress sources such as density contrasts and active
faults systems in some plates have high impact in comparison to plate boundary forces and control the stress pattern.