Characterizing Complex Surface Ruptures in the 2013 Mw 7.7 Balochistan Earthquake Using Three‐Dimensional Displacements

Abstract

AbstractWe use satellite‐derived high‐resolution topography and orthoimages, namely, preearthquake Advanced Land Observing Satellite World 3‐D data and postearthquake Pleiades data, to retrieve 3‐D displacements in the 2013 Balochistan, Pakistan, earthquake. Previous studies of this earthquake have revealed many complex rupture patterns, such as off‐fault deformation (near‐field strike‐slip displacements smaller than the far field) and inelastic surface deformation (horizontal shortening on the surface significantly larger than that from simple elastic model). In this paper, we reanalyze the complexities of surface ruptures in a systematic way using the newly derived 3‐D displacements. In doing so, we made use of the vertical component of the curl and the horizontal divergence of the displacement field. By comparing the off‐fault deformation and curl field along the rupture, we found that curl is a good measure of the width of the deformation zone. The curl width ratio (CWR)—the ratio of the basic resolution of the curl field and curl width—was used to quantify the degree of surface slip localization. When CWR ≥ 0.9, there is no or very little off‐fault deformation, whereas when CWR ≤ 0.6, surface deformation is almost 100% distributed. The distributed deformation observed is controlled by both the fault geometry and local material types. Despite the overall strike slip with some thrusting, the divergence shows localized extension or enhanced shortening in the near field due to fault geometric variations at a spatial scale of tens to hundreds of meters, consistent with the 3‐D displacements and geological interpretations.