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

Abstract

On 16 September 2015, a moment magnitude (Mw) 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.

Tsunami Source Inversion Using Tide Gauge and DART Tsunami Waveforms of the 2017 Mw8.2 Mexico Earthquake

“…Since then, this method has been revised and applied to primary interplate tsunamigenic earthquakes that have occurred in subduction zone regions around the world (e.g., Fujii and Satake 2007;Fujii et al 2011;Gusman et al 2015;Adriano et al 2016b;Yoshimoto et al 2016Yoshimoto et al , 2017Williamson et al 2017). This method has also proven to be useful for solving intraplate earthquakes with complex focal mechanisms (Gusman et al 2017a, b).…”

“…1, A ij (t) is the Green's function at the i-th station from the j-th subfault, x j is the unknown slip on the j-th subfault, and b i (t) is the tide gauge record at the i-th station (Satake 1987). Theoretically, each subfault patch behaves independently of the neighboring segments, providing a best fit to the Green's function (Williamson et al 2017). Thus, our inversion model does not include any smoothing factor for the slip calculation.…”

Integrated geophysical characteristics of the 2015 Illapel, Chile, earthquake

“…[], An and Meng [], and Williamson et al . [] models do not have significant shallow slip at depths less than 10 km. Finally, we do not interpret differences in peak slip amplitude, since there are multiple possible explanations for the variability, including the resolution inherent in the observations, smoothing or other regularization constraints, model elastic properties, and subfault dimensions.…”

“…In addition to the seismic and geodetic slip models presented in this study, numerous other slip distributions have been published for the Illapel earthquake. These include models inverted from a variety of data sets: teleseismic broadband waveforms [ Ye et al ., ; Lee et al ., ], teleseismic broadband data augmented by tsunami observations [ Heidarzadeh et al ., ; Li et al ., ], joint teleseismic broadband, regional strong motion, high‐rate GPS, static GPS, and InSAR [ Tilmann et al ., ], joint high‐rate GPS, strong motion, InSAR, and tsunami [ Melgar et al ., ], joint tsunami and static GPS and InSAR [ An and Meng , ; Williamson et al ., ], and static geodetic observations alone [ Barnhart et al ., ; Ruiz et al ., ; Feng et al ., ]. Because the various geophysical observations are sensitive to different aspects of the deforming subduction system and the model setups and inversion approaches differ, there are differences in the precise timing (in kinematic models), distribution, and amount of slip.…”

Insights Into the Kinematic Rupture of the 2015 Mw 8.3 Illapel, Chile, Earthquake From Joint Analysis of Geodetic, Seismological, Tsunami, and Superconductive Gravimeter Observations

“…The estimated historical source regions are shown in Figure 1. With the exception of the 1939 intraplate normal fault event that occurred in the intermediate depth within down-going slab (Beck et al, 1998), all of these megathrust earthquakes are caused by the subduction of the Nazca plate to the overriding South American plate at a convergence rate of about 6.8 cm/year in a N78°E direction 2016; Grandin et al, 2016;Klein et al, 2017;Ruiz et al, 2016;Shrivastava et al, 2016;Zhang et al, 2016), or combinations of multiple data sets Li et al, 2016;Melgar et al, 2016;Tilmann et al, 2016;Williamson et al, 2017). The first-order slip pattern of the 2015 Illapel earthquake is basically consistent among those studies mentioned above, and the slip distribution along strike can be well resolved by the onshore observations.…”