A Travel‐Time Path Calibration Strategy for Back‐Projection of Large Earthquakes and Its Application and Validation Through the Segmented Super‐Shear Rupture Imaging of the 2002 Mw 7.9 Denali Earthquake

Abstract

Detailed constraints on rupture processes of large earthquakes are crucial for understanding fundamental earthquake physics. To image the rupture process of large earthquakes, back-projection (BP) of high frequency (HF) tele-seismic array waveforms is one of the commonly used techniques in the last 15 years or so (e.g., Kruger & Ohrnberger, 2005). Assuming delta-function shaped Green's functions and taking advantage of the reciprocity between sources and receivers, BP methods trace the location and timing of HF sources by either maximizing the stacking power of back-propagated array data in the time domain (e.g.,

Simultaneous Rupture Propagation Through Fault Bifurcation of the 2021 Mw7.4 Maduo Earthquake

“…The rupture speed of the Maduo earthquake was quite stable around 2.5 km/s, which is in contrast with supershear rupture speed derived from the other BP analysis (Yue et al, 2022;Zhang et al, 2022). The primarily reason for this discrepancy could be that we applied travel time path calibrations (see more details in Zeng et al (2022)) but the other BP studies did not. The rupture did not slow down at the bends and step-overs.…”

“…(c) The BP conducted in our study has been calibrated by the aftershocks to account for the source-side 3D velocity structure effect, such calibration was not performed in . We showed in the aftershock BP relocation (Figure S20 in Supporting Information S1), as well as in Zeng et al (2022) that, such path calibration is needed for higher resolution BP results.…”

“…The primarily reason for this discrepancy could be that we applied travel time path calibrations (see more details in Zeng et al. (2022)) but the other BP studies did not. The rupture did not slow down at the bends and step‐overs.…”

“…We compare the differences between the BP locations and the refined epicenter locations for these events (W Wang et al, 2021). Note that our calibration events include the earthquakes away from the mainshock rupture zone (Figure S19 in Supporting Information S1), such selection was shown to be more accurate for travel time error interpolation (Zeng et al, 2022). After trying different groups of calibration events, it appears that we need to use different calibration event combinations to obtain high consistency between the calibrated BP locations and the refined epicenters for the events located to the east and west of the mainshock epicenter, respectively (Figure S19-S20 in Supporting Information S1).…”

“…To resolve its high frequency radiation and the rupture speed of the Maduo earthquake independent from FFM and MPS solutions, we perform a MUltiple SIgnal Classification BP analysis (Meng et al., 2011; Zeng et al., 2020) using high‐frequency (0.3–1.0 Hz) teleseismic P‐waves recorded by the European array (EU) and Australian array (AU) (Text S4 in Supporting Information ). To take into account the potential impact of the 3D source‐side velocity structure on the travel time, we apply a path calibration algorithm using the arrival times of mainshock and other nearby events, which was proved to be necessary for more accurate BP analysis (Zeng et al., 2022). The effectiveness of the calibration is verified by applying it to the BP analysis of the M > 5 aftershocks.…”