New Insights into the 2009 Harrat Lunayyir Dike Intrusion from InSAR, Stress Calculations and Analog Experiments

Abstract:

Previous studies of the 2009 Harrat Lunayyir (western Saudi Arabia) dike intrusion have shown extensive ground deformation. However, these studies did not report fully the spatial and temporal evolution of ground deformation during majority of the activity. Here we use additional InSAR observations, stress calculations and analog experiments to unravel the sequence of events during the intrusion and to analyze the interaction between the intruding dike and normal faulting at Harrat Lunayyir. We find that surface deformation is first observed in data from 16 May, about four weeks after the earthquake activity started, when surface displacements due to a ~1.9 m thick dike intrusion are observed. From 19 May, the dike propagated to within ~1 km of the surface, with graben-bounding normal fault displacements dominating the near-field deformation. The volume of the dike increased gradually from a total of ~0.06 km³ on 16 May to ~0.13 km³ on 17 June. Coulomb failure stress-change calculations of the dike-fault interaction show that the growing dike caused extension above its tip and triggered slip on the graben-bounding normal faults. In return, the faulting lead to compression around the upper tip of dike, holding back its vertical propagation. Our analog experiments show that the wedge-shape graben at the surface is consistent with the asymmetric arched shape of the dike at shallow depth.