Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
gravity models and then upward continued to various levels to determine the minimum elevation to
which GOCE gradient data must be downward continued to resolve subsurface structures.
Figure 2. Image of simulated gravity gradients from the European Space Agency (ESA).
(http://www.esa.int/).
Isostatic gravity anomalies as an indicator of seismic moment release
The GOCE gravity field and gradients could also be used to map asperities in convergent zones in
conjunction with seismic b-values. The locations of the largest co-seismic slips (asperities) on the fault
plane of the Antofagasta earthquake (1995) of Mw equal to 8.0 in northern Chile have been mapped
using the spatial distribution of the seismic b-values obtained from the aftershock sequence of the
mega-thrust earthquake and a high resolution isostatic gravity field. The co-seismic high moment
release and isostatic residual anomalies are superimposed on the seismogenic part of the north
Chilean subduction zone where the strongest coupling of upper and lower plate is expected. The
observed positive correlations between high seismic b-values, isostatic anomalies, and geologic
structures enabled a mechanical model for the generation of asperities in the Antofagasta region to be
proposed. The results suggest that the batholiths in conjunction with buoyant forces acting on the
subducted slab of the Nazca plate are responsible for locking the interface where asperities are
located. This implies that long-term conditions for the existence of an asperity generating tectonic
situation are present. Consequently, the asperities around Antofagasta could be stationary features, at
least for several seismic cycles, implying that isostatic anomalies of active segments of convergent
margins can be used as an indicator for high moment release and slip of future large earthquakes
(Figure 3).
References
Delouis, B., 1996, Subduction et deformation continentale au Nord-Chili : These de doctoral, Univ.
Louis Pasteur de Strasbourg, France.
Förste, C., Schmidt, R., Stubenvoll, R., Flechtner, F., Meyer, U., König, R., Neumayer, H., Biancale,
R., Lemoine, J.-M., Bruinsma, S., Loyer, S., Barthelmes, F., and Esselborn, S., 2008, The
GeoForschungsZentrum Potsdam/Groupe de Recherche de Gèodésie Spatiale satellite-only
and combined gravity field models: EIGEN-GL04S1 and EIGEN-GL04C: Journal of Geodesy,
82, 331-346.
Sobiesiak, M. M., Meyer, U. Schmidt, S., Götze, H. J., Krawczyk, C., 2007, Asperity generating upper
crustal sources revealed by b-value and isostatic residual anomaly grids in the area of
Antofagasta: J. Geophys. Res., Vol. 112, B12308, doi: 10.1029/2006JB004796.
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