E) Gravity Anomalies:
Mechanical modeling of Bouguer gravity anomalies is a good way to study plate interactions at depth. Basically, gravity anomalies reflect lateral variations in density at depth and helps us to understand to what degree surface deformation reflect deformation in the mantle. In order to maintain isostatically the elevation of Tibetan plateau, the crustal thickness beneath it, should be doubled compared to most of continental crust. Jin et. al. (1996) applied forward flextural modeling by examining fits to the gravity profile (figure 18).
Figure 18. A) Fit to the Bouguer gravity data along NNE-SSW trending profile for a model in which elastic plate
thickness varies and plates are subjected to bending moments by subducting slab. B) Interpreted crustal structure
of Tibetan plateau corresponding to the gravity fit and its comparison with seismic reflection data and earthquake
seismicity [Jin et al. 1996].
According to their model the Indian plate is subducting beneath the Eurasian plate for a distance of 500-700 km north of Main Frontal Thrust (MFT). As a result, stiff Indian plate which weakens beneath Himalaya underthrusts until Yarlong-Zangpo Suture (YZS) and is subject to a bending moment. North of YZS, gravity data was interpreted as the result of a mantle suture between Indian and Asian plates underthrusting from both ends.
Non uniqueness of the interpretation, is the major problem of gravity based flextural models. In this case, gravity agrees with geophysical data and suggests southward subducting Asian mantle in addition to Indian plate.
A) Tectonics & Geology B) Seismicity C) GPS D) Seismic profiles & Tomography
E) Gravity F) Anisotropy G) Paleomagnetism H) Geochemistry I) MT studies
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