Reconstruction of coseismic slip from the 2015 Illapel earthquake using combined geodetic and tsunami waveform data

On 16 September 2015, a moment magnitude (M_w) 8.3 earthquake struck off the coast of central Chile, generating a large tsunami with nearby coastal wave heights observed on tide gauges in Chile and Peru of up to 4.7 m and distal observations of over 40 cm in the Kuril Islands across the Pacific Ocean. Through a transcoastal geodetic study, including tsunami time series recorded at open ocean pressure gauges, subaerial deformation observed through interferometric synthetic aperture radar from the Sentinel-1 A satellite and continuous GPS, we identify the location and extent of coseismic slip. We find that most coseismic slip was concentrated in a patch immediately offshore, with little modeled slip near the trench. This result satisfies the tsunami waveforms measured in the deep ocean north of the rupture area, with wave heights up to 10 cm. While the event exhibits some features of a slow tsunami earthquake (moderately large tsunami and possible slow second-stage rupture), our inversion results do not require substantial near-trench rupture. However, the prevalence of large and shallow thrust along subduction megathrusts along central Chile raises the question of the likelihood of future such events and the implications for future hazardous tsunamigenic earthquakes.