Fig. 8

Structural map showing gravity trends (thick dashed lines) interpreted as inherited Precambrian faults, aeromagnetic trends (thin dotted lines) related to Cenozoic dykes, normal faults evidence by InSAR (Baer and Hamiel 2010) (green lines), and Harrat area represented by a grey polygon. The map also shows the spatial distribution of relocated epicenters for the events listed in Additional file 1: Table S1. The 2009 HL seismic activity was described as a swarm-like earthquake sequence with a pattern that began with a swarm activity denoted by the events 1–35 (triangles) that delineated the NE fault trend; the foreshock–mainshock stage represents the events 36–109 (circles) that are located over the NNW fault trend and the aftershock stage represents the events 110–136 (diamonds) that distributed over the NNW fault trend. The red dashed line represents the fault trends identified from the distribution of epicenters