Figure 5
Left panel displays the hypocenters of the aftershock sequence, superimposed on the seismic section (see track line in Fig. 2) that was shot during the Seismamara cruise28,36,56 in 2001 in the Western High area. The migration was obtained after stack and time-migrated, by using 5 main velocity intervals based on velocity analysis for the sedimentary layers and constraints from refraction modelling for the crust: the water-column, the shallow sediment interval, the deep sediment interval, the interval between the basement and the detachment, and the crustal layer below the detachment. Velocity in the water is settled constant at 1500 m/s and velocity increases linearly in other intervals. The average velocity in the shallow sediment is 1700 m/s, 2400 m/s for the deep sediment interval, 3300 m/s between the acoustic basement and the detachment, and is 5500 m/s in the crust below the detachment. Line-drawing (partly based on ref.37, page 160) is displayed in right panel along with the locations of the aftershocks that followed the M 5.1 earthquake of July, 25, 2011. Continuous red line indicates the MMF. The dotted line within the sedimentary basin indicates the east-west oriented, secondary fault displayed in Fig. 4. The earthquakes (at depths between 2 and 4 km) that were used to compute the composite focal mechanism using HASH38,39 are listed in Appendix 3. Image created with GMT software, Version 4.5.11.
