Modeling tsunami observations to evaluate a proposed late tsunami earthquake stage for the 16 September 2015 Illapel, Chile, M_w 8.3 earthquake

Abstract

Resolving seaward extent of slip during great subduction zone interplate ruptures using land‐based seismological and geodetic observations is challenging. Modeling of tsunami recordings from ocean‐bottom pressure sensors of the Deep‐ocean Assessment and Reporting of Tsunami (DART) network has added valuable constraints on near‐trench slip for recent events. We use DART and tide gauge recordings to evaluate a proposed seismological scenario involving a late Mw 8.08 tsunami earthquake following the ~95 s long main rupture stage of the 16 September 2015 Illapel, Chile, Mw 8.3 earthquake. Tsunami observations constrain the spatial extent of any late tsunami earthquake slip to locate north of the main shock hypocenter. The proposed late shallow slip predicts tsunami signals with considerable amplitudes but shorter wavelengths compared to those of the main stage slip constrained by joint seismic and tsunami modeling, yielding overprediction of first‐arrival amplitudes at DART and tide gauge stations when the two stages are combined.

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

“…Relatively large mismatches are found at stations qtro and buca ( Figure 7) where our simulations are approximately 4-5 min earlier than observations. This can be probably attributed to the mislocation of slip near the trench, which has been verified by Lay et al (2016) and Heidarzadeh et al (2016). In general, our preferred model is robust enough to independently predict the tsunami observations.…”

Optimal time alignment of tide‐gauge tsunami waveforms in nonlinear inversions: Application to the 2015 Illapel (Chile) earthquake

“…Second‐order differences with other models regard the details of the slip pattern and the maximum slip values. For example, the model by Lee et al [] which inverted teleseismic data contains a secondary and significant shallow patch of slip south of ~32°S, which is not present in our preferred slip model nor in the model by Lay et al []; however, we did not analyze the possible trade‐off caused by delayed slip with rupture position and the retrieved time shifts. The source model by Melgar et al [] could be viewed as an intermediate model between our preferred model obtained by applying OTA (Figure a) and the slip distribution we retrieved when the OTA is not applied (Figure b).…”

“…We propose an approach to the tsunami data inversion that takes into account possible time shifts between observed and predicted tsunami signals. In seismological studies [e.g., VanDecar and Crosson, 1990;Mercerat and Nolet, 2013;Kimman, 2016;Yuan et al, 2016] time shift issues of seismic waveforms which arise for a number of different reasons (e.g., inaccuracies of the Earth seismic velocity model, simplifying assumptions about the source time function or in the wave propagation theory) are often considered and addressed in various ways. For example, in double-difference seismic tomography the time shift between observed and synthetic seismic waveforms has been mapped into the seismic velocity model by using waveform cross correlation [Zhang and Thurber, 2003].…”

Evaluating the Updip Extent of Large Megathrust Ruptures Using Pcoda Levels

“…For example, a proposed second-stage tsunami earthquake at shallow depth during the source rupture process for the 2015 Illapel (M W 8.4) earthquake was inferred based on observation of prolonged teleseismic P wave ground motions (Lee et al, 2016). However, Lay et al (2016), An et al (2017), and Qian et al (2019) demonstrate that the P coda could be explained without any prolonged rupture by improved modeling of the water reverberations generated by shallow slip. Nonetheless, ambiguity exists regarding which source rupture attributes and source region structural features are important for exciting strong P coda amplitudes (Fan & Shearer, 2018;Ihmlé & Madariaga, 1996;Ward, 1979;Wu et al, 2018;Yue et al, 2017).…”