Coulomb stress change imparted by the magnitude 7.6 mainshock to the surrounding faults, calculated in three different ways. In the left panel, faults are assumed to be aligned parallel to the mainshock rupture surface, which suggests earthquake promotion in a semi-circular arc to the east, north and south of the mainshock (the red blur that extends to the Philippine Trench). In the middle panel, smoothed focal mechanisms (“beachballs”) from the global compilation by Kagan and Jackson (2014) show more strongly promoted failure to the east. In the right panel, actual focal mechanisms from the Global CMT catalog are used, with stress calculated at their depths, which more strongly promotes failure to the north of the mainshock. It’s unclear which of these inferences best represents the triggering likelihood, but we would place more confidence in the right panel, because these are actual faults. Credit: Temblor, CC BY-NC-ND 4.0