Phys.org February 8, 2022
The 2021 August South Sandwich Island Mw 8.2 earthquake was a surprise, because it was initially reported as a magnitude 7.5 event at a deep depth (47 km) but generated a global-spreading tsunami that would only be expected for a larger and shallower event. By using seismic data researchers at Caltech revealed a hidden Mw 8.16 shallow slow event that happened between clusters of regular ruptures in the beginning and end. Although the slow event contributed 70% of the seismic moment, lasted three minutes, and ruptured a 200-km section of the plate interface, it is essentially invisible at short or intermediate periods, which explains its anomalously low body-wave and surface-wave magnitudes. The earthquake represents an extreme example of the broad spectral behaviors of subduction zone earthquakes and calls for attention in the research and warning of similar events. According to the researchers their result is qualitatively consistent with other moment tensor solutions and the deviant mB–Mw and MS–Mw relations and provides a more quantitative space-temporal pattern of this unusual sequence…read more. Open Access TECHNICAL ARTICLE
Overview of the tectonic setting and seismicity… Credit: Geophysical Research Letters, Volume49, Issue 3, 16 February 2022, e2021GL097104