How fast is rupture during an earthquake?: New insights from the 1999 Turkey earthquakes

We report that during the two devastating 1999 earthquakes in Turkey, rupture propagated over a large part of the nearly 200km long fault zone at supershear speed approaching 5km/s. We present observations and modeling which confirm the original inference of supershear rupture during the Izmit earthquake and we show that supershear rupture also occurred during the Duzce earthquake. We show that the rupture velocity measured - about root2 times the shear wave velocity - is the value predicted by theoretical studies in fracture dynamics. We look for clues to explain these observations.