Significance of near-field geodetic data and diversified geometries of acquisition to model coseismic slip and refine shallow slip deficit: the case of the Balochistan earthquake (2013, Mw 7.7, Pakistan)

The 2013 Mw 7.7 Balochistan earthquake ruptured the Hoshab fault (Pakistan) and was dominated by left-lateral slip with some reverse component. This event is one of the few earthquakes that benefit from a rich satellite imagery coverage with optical and radar data. This coverage offers an opportunity to measure coseismic displacements in many directions both in near-field and far-field, allowing us to address the question of earthquake dynamics modeling using geodetic data with different geometries of acquisition.

Our optical dataset consists in offset fields computed from Landsat 8 (15-m pixel) and SPOT 5 (2.5-m pixel) images. We also process SAR data from RADARSAT-2 and TerraSAR-X to produce interferograms and radar correlations. Since the ScanSAR mode of TerraSAR-X induces particular pre-processing steps before computing interferograms, we developed new tools to enable data reading, bursts handling and phase corrections.

Exploiting such a diversified dataset has been the opportunity to bring new elements on the understanding of data complementarity and weighting, which are significant points of the fault geometry and coseismic slip modeling process. In particular, we show that no weighting is necessary between InSAR on one hand and optical and radar correlations on the other hand.

Finally, in line with recent studies (Vallage et al. 2015, Xu et al. 2016, Marchandon et al. 2018) we infer that no shallow slip deficit occurred during the Balochistan earthquake. We thus suggest that near-field data is a methodological key point to enhance earthquake modeling and shallow slip deficit refinement.