On 2015 september 16, a large magnitude earthquake (Mw 8.2 to 8.3) occurred offshore Central Chile coast close to the town of Illapel in the Coquimbo region about 250km north of Santiago (UTC time 22:54 on Sept. 16, Chilean time 19:54).
Chile Illapel earthquake Mw8.3 - 16 Sept 2015 - Aftershocks 4 days after main shock - Rough probable extension of coseismic rupture in orange.
The seismic rupture broke the subduction interface between the Nazca and South American plates, with an hypocenter located at 20-25 km depth. Focal plane solution shows that it is a "classical" subduction earthquake: coseismic slip occurred on the subduction megathrust which dips gently towards the east under the South American continent. Rupture appears to have propagated updip from the hypocenter and likely reached the trench. It also propagated in a north-south direction, parallel to the trench, and reached a total rupture length of about 200km.
That segment of the plate boundary already broke in 1943 with a magnitude estimated between 7.9 and 8.3 depending on studies. The possibly higher magnitude of the 2015 September 16 earthquake might be due to a propagation farther to the south or to larger coseismic slip. The tsunami that hit the chilean coast reached wave heights up to 4-5m. It seems to have been stronger than 1943 one, again suggesting larger coseismic slip and/or a shallower propagation of the rupture. Tsunami waves crossed the Pacific ocean with significant attenuation (heights of about 1.5m in Marquesas, and 1m in Hawaii).
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