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Abstract:
Two earthquakes struck eastern Turkey and caused severe damage on 6th February 2023. The magnitudes are Mw7.8 and Mw7.7, respectively. The rupture processes of the two earthquakes are significantly different. The Mw7.8 earthquake has a gradual initial rupture, resulting in a longer duration time. In addition, the epicenter is located at a small branch.We focus on the initial rupture constrained by teleseismic data. We set up fault planes based on preliminary online geodetic and seismology results by other researchers. After a series of tests, we could not simulate the initial rupture well based on the uniform sub-fault size (6x4km). We carry out a two-step inversion strategy. Firstly, we used a rectangle fault with a length of 26km and a width of 30km to simulate the first 12s teleseismic P waveforms. The sub-fault size is 2x2km. The strike and dip angles are 220° and 70°, respectively. The residual teleseismic waveforms between synthetic and the whole observed teleseismic waveforms are calculated.Secondly, Two rectangle segments with larger sub-fault sizes and different strike angles (220° and 235°) are applied to simulate the residual teleseismic waveforms. The sub-fault size is 6x4km.The result indicates that the initial rupture propagated downward along the dip-slip direction which is a nearly pure strike-slip event. The moment is 1.3x10^19 Nm, and the corresponding moment magnitude is Mw6.7, about 2% of the total moment.A significant normal component could be observed at the shallow depth between the initial pure strike-slip patch and the body patch, which is consistent with the tectonic background.
