Coherent Seismic Arrivals in the P Wave Coda of the 2012 M_w 7.2 Sumatra Earthquake: Water Reverberations or an Early Aftershock?

Abstract

Teleseismic records of the 2012 Mw 7.2 Sumatra earthquake contain prominent phases in the P wave train, arriving about 50 to 100 s after the direct P arrival. Azimuthal variations in these arrivals, together with back‐projection analysis, led Fan and Shearer (, https://doi.org/10.1002/2016GL067785) to conclude that they originated from early aftershock(s), located ∼150 km northeast of the mainshock and landward of the trench. However, recently, Yue et al. (, https://doi.org/10.1002/2017GL073254) argued that the anomalous arrivals are more likely water reverberations from the mainshock, based mostly on empirical Green's function analysis of a M6 earthquake near the mainshock and a water phase synthetic test. Here we present detailed back‐projection and waveform analyses of three M6 earthquakes within 100 km of the Mw 7.2 earthquake, including the empirical Green's function event analyzed in Yue et al. (, https://doi.org/10.1002/2017GL073254). In addition, we examine the waveforms of three M5.5 reverse‐faulting earthquakes close to the inferred early aftershock location in Fan and Shearer (, https://doi.org/10.1002/2016GL067785). These results suggest that the reverberatory character of the anomalous arrivals in the mainshock coda is consistent with water reverberations, but the origin of this energy is more likely an early aftershock rather than delayed and displaced water reverberations from the mainshock.

Teleseismic Waveform Complexities Caused by Near Trench Structures and Their Impacts on Earthquake Source Study: Application to the 2015 Illapel Aftershocks (Central Chile)

“…However, Yue et al () argued that these coda waves are more likely produced by water reverberations. More recently, Fan and Shearer () presented more waveform analysis to demonstrate that the reverberation characteristics of the anomalous arrivals in the mainshock coda is consistent with water reverberations, but the origin of this energy is more likely due to an early aftershock rather than delayed and displaced water reverberations from the mainshock. A deterministic 3‐D simulation with more realistic model (e.g., bathymetry and water) could possibly shed some new lights on these debates.…”

Evaluating the Updip Extent of Large Megathrust Ruptures Using Pcoda Levels

“…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). Recent three-dimensional studies by Qian et al (2019) and Wu et al (2018) conclude that the bathymetry and sedimentary layers have strong effects on enhancing P wave coda oscillations in addition to the location of earthquake slip.…”

Consecutive ruptures on a complex conjugate fault system during the 2018 Gulf of Alaska earthquake

“…It is possible that the complex waveforms observed during the 2018 Gulf of Alaska earthquake were contaminated by reverberations due to the bathymetric setting that cannot be reproduced by the theoretical Green's function, resulting in dummy multiple events [41][42][43][44] . We evaluated this possibility by using empirical Green's functions 45,46 and confirm that it is unlikely that the multiple rupture stages originated from such reverberations (see Supplementary Material S3 and Fig.…”