2.Moment Tensor of the 7 May 2020 M5.1 mainshock
The low-frequency full waveforms of the mainshock recorded by eight Iranian broadband seismic network (BIN) stations situated at distances ranging from 84 km to 433 km (Fig. 1a) were inverted to obtain the moment tensor, assuming a point source. The BIN seismic network is maintained by the International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran. More distant stations were excluded from the inversion to keep the maximum possible frequencies of the displacement waves while avoiding the undesirable effects of crustal heterogeneity on the centroid location and moment tensor calculations. The moment tensor inversion was carried out using the latest version of Isola code (Sokos and Zahradnik, 2008). The mean and trend of data were removed and bandpass filtered by fourth-order Butterworth filter between 0.03- 0.08 Hz and cut from origin time for a length of 250 s. The Green’s functions for the trial point source were computed using the discrete wavenumber (DWN) method (Bouchon, 2003) and the similarity between the observed and calculated waveforms measured by the Variance Reduction (VR) parameter of the Isola code. Details of the inversion procedure are explained in a paper by Momeni and Tatar (2018). We used a velocity model of the area obtained in a detailed microseismic study by Tatar et al., (2012) (Table S2). The trial point sources were grid searched in the activate area (Fig. 2a). The centroid time was searched as well, from 2 s before to 4 s after the origin time with steps of 0.08 s (Fig. 2b). The best wave-form fit was obtained for a point source situated at ~4 km WNW of the hypocenter reported by IRSC, at a depth of 12 km, with a space-time correlation of 85%, proposing that the rupture grew mostly to the West (toward Tehran city). The NW-SE striking nodal plane has a strike/dip of 291°/60° (Figs. 2, 4a), which is steeper than the one obtained by IRSC (52°). However, that is less steep compared to the GCMT result (68°). The centroid depth could change between 11 km to 16 km, with only a slight change in the waveform-fit (<2%). A total scalar seismic moment of 4.8 E+16 Nm equivalent to Mw 5.1 was computed, which is larger than the GCMT and IRSC results (4.1*E+16 Nm and 2.8*E+16 Nm, respectively.