Outer rise seismicity boosted by the Maule 2010 Mw 8.8 megathrust earthquake

Abstract

The Maule 2010 megathrust earthquake Mw 8.8 has been characterized by two coseismic high-slip patches (asperities) north and south of the epicenter, separated by a region of lower slip. Here, we invert full broadband waveforms to obtain regional moment tensors, yielding precise centroid depth and source parameters of outer rise events (Mw>4.5), including a large Mw 7.4 event that occurred just 1.5h after the Maule mainshock. Outer rise seismicity occurred mainly in two clusters: (1) a large number of outer rise events in the subducting plate located just seaward of the northern asperity of the Maule earthquake, and (2) a second cluster with fewer events seaward of the southern edge of the Maule rupture area. Thus, the outer rise seismicity is correlated with the coseismic rupture of the Maule earthquake, reflecting the stress state of the interplate coupled zone. The moment tensor results indicate similar extensional focal mechanisms for all outer rise events in the northern zone. In the southern region, most of the outer rise events are also extensional, except for one strike slip event located near the oceanic Mocha Fracture Zone. The centroid depths vary from 5 to 20km depth, and present similar magnitudes. Many of the outer rise events nucleated near the Mocha Fracture Zone, including the Mw 7.4 event and one strike–slip event. The calculated yield strength envelope for the oceanic Nazca lithosphere suggests that the centroid depths of intraplate tensional events span almost the entire upper-brittle part of the oceanic lithosphere.