The 2021 South Sandwich Island Mw 8.2 earthquake: a slow event
sandwiched between regular ruptures
Abstract
We determined the rupture sequence of the Aug 12, 2021 Mw 8.2 South
Sandwich Island earthquake which, according to the reports from the
National Earthquake Information Center, appears to be a complex sequence
in both time and space. Notable tsunamis were recorded by tide gauges at
global distances. Given the complexity of this event, we used a multiple
subevent inversion method that can accommodate complex variations of
fault geometry, location, depth, and temporal characteristics of the
event. We found that the rupture initiated as a regular deep thrust
earthquake; it then triggered a shallow dominantly slow subevent
extending ~200 km to the south, and ended with 2 other
regular subevents. The total duration is ~260s,
unusually long for an Mw 8.2 event. Our result is qualitatively
consistent with other moment tensor solutions and the observed mB-Mw and
MS-Mw relations, and provides a more quantitative space-temporal pattern
of this unusual sequence.