Backprojection Imaging Based on a 3D Model: Method and Applications on the 2017 Mww8.1 Mexico Earthquake and Mw7.7 Russia Earthquake

In this study, we carried out a backprojection (BP) analysis to image the rupture process of the newly happened September 8, 2017 Mww8.1 Mexico earthquake based on a global 3D P-wave tomography model, the LLNL-G3Dv3 model. Limited to epicenter distance and data quality, only waveform observation data from Alaska (AL), USA was utilized finally, with some data from South America (SA) as supplement. First, we compared the HF BP results of 1D and 3D model to illustrate the higher resolution and reliability of the 3D one. Then we discussed the consistency among the overall rupture pattern, the main event focal mechanism and aftershocks distribution, and further inferred the possible fault geometry. After that, we explained the rationality of the setting for rupture duration based on beamforming energy pattern, normalized power variation and other previous works. We then seriously examined the creditability of stage 2 and explained why speed in stage 2 is much bigger than in 1. Finally, we obtained the coulomb stress change imparted on the faults of the subsequent September 19 Mww7.1 event and September 23 Mww6.1 event to find out if they are positively triggered by this main event. From our current research, the complete ~53s rupture process of this earthquake can be divided into two stages. In stage 1, which lasted for ~37s, the rupture propagated from the epicenter towards the NW direction (~330°measured from north clockwise) with a speed of ~2.8 km/s, and extended to a length of ~89 km. Then it made a right turn and shortly after, it continued to propagate to near N (~3°) with a higher speed of ~5.3 km/s and a scale of ~75 km. Our study intended to believe that the Mww8.1 event has almost nothing to do with the Mww7.1 event while it strongly triggered the occurrence of the latter Mww6.1 event.