Regional moment tensor inversion for strong aftershocks of the August 17, 1999 Izmit Earthquake (Mw=7.4)

We analyzed the source mechanisms of the thirty largest aftershocks (4.0 ≤M_L ≤ 6.2) of the August 17, 1999 Izmit earthquake (M_w=7.4) by applying the Regional Moment Tensor inversion method using data from near-regional broadband stations. The inversion solutions were compared to 17 well-constrained first motion solutions, and were seen to be in good agreement. We found that the dominance of strike-slip motion is the main characteristic of the Izmit earthquake sequence. Significant aftershock activity was recorded to the west and east of the un-ruptured extremities. In the east the aftershocks located near the town of Düzce represent an early replica of the November 12, 1999 Düzce earthquake (M_w=7.2) in terms of locations and source mechanisms. In the Marmara Sea, where the fault geometry is still very poorly resolved, most aftershocks have right lateral strike slip solutions with strike direction parallel to the submerged branches of the North Anatolian Fault.