The 19 September 2017 ( M _w 7.1) Intermediate‐Depth Mexican Earthquake: A Slow and Energetically Inefficient Deadly Shock

We investigate dynamic source parameters of the M(w)7.1 Puebla-Morelos intermediate-depth earthquake (h = 57 km) of 19 September 2017, which devastated Mexico City. Our simple, elliptical source model, coupled with a new Particle Swarm Optimization algorithm, revealed rupture propagation within the subducted Cocos plate, featuring a high stress drop (Delta tau = 14.9 +/- 5.6 MPa) and a remarkably low radiation efficiency (eta(r) = 0.16 +/- 0.09). Fracture energy was large (G = (1.04 +/- 0.3) x 10(16) J), producing a slow dissipative rupture (V-r/V-s = 0.34 +/- 0.04) with scaling-consistent radiated energy (E-r = (1.8 +/- 0.9).10(15) J) and energy-moment ratio (E-r/M-0 = 3.2 x 10(-5)). About 84% of the available potential energy for the dynamic rupture was dissipated in the focal region, likely producing friction-induced melts in the fault core of 0.2-1.2 cm width due to heat production (700-1200 degrees C temperature rise). Such source features seem to be a universal signature of intermediate-depth earthquakes.