4.2.1. Rupture process using one elliptical slip patch
Ten final rupture models resulted from different inversions of the near field displacement waveforms are evaluated (see Fig. 3a; Table S3). They describe the mainshock slip using one elliptical slip patch. These rupture models were calculated on a planar fault with a strike/dip of 292°/60°N and with the hypocenter obtained in section-3. They have a minimum wave misfit of ~42%. Most of the misfit is due to the late part of the displacement fields which mainly contain the surface waves and site effects (see figures S2 to S11). For all of these models, the slip extends to the West of the hypocenter with large values located at depths ranging between 13 km to 10 km. This range is within our obtained depth range for the maximum waveform correlation in the moment tensor inversion as well as the IRSC result. The rupture has a left-lateral strike-slip mechanism (rakes =14°-18°) and does not reach the surface.
All the models had sub-shear rupture speeds between 2.2 km/s to 2.8 km/s (Vs=3.5 km/s) and almost the same duration, between 2.1 s to 2.8 s. The rise time changes between 0.02s to 0.26s. Models with higher rise times exhibit mostly higher rupture speeds, which is consistent with the results of dynamic simulations from Schmedes et al. (2010). The maximum slip changes from 3 cm to 9 cm, depending on the rupture dimension.
The inversions converge to a seismic moment release between 3.8e+16 Nm to 4.3e+16 Nm, which are smaller than the estimated scalar moment obtained by regional waveform inversion (4.8 e+16 Nm). We stress that the low-frequency noises in the strong motions limited inversion to use frequencies below 0.08 Hz. While in section 2, we use frequency ranges down to 0.03 Hz. All the rupture models can satisfy the strong motion data. We make an average of the ten final models as our preferred model. This rupture model shows nucleation at the depth of ~14 km (Fig. 4a). The slip mostly extends toward the west and to the shallow depths with an average speed of 2.75 km/s. The maximum slip is estimated as ~4 cm between depths ranging from 13km to 11km. The rupture lasts for ~2.8 s and releases a total scalar seismic moment of 4.04 E+16 Nm equal to Mw 5.0. That is less than the point-source moment tensor results in section 2. The maximum slip is situated 2.5 km West and ~0.5 km South of the hypocenter and at a depth of 12 km. The rupture stops at a depth of 10 km. The rupture length of ~9 km for an M5.0 event is remarkable, proposing its comfort extension.