Did stress triggering cause the large off-fault aftershocks of the 25 March 1998 M_W=8.1 Antarctic plate earthquake?

The 1998 Antarctic plate earthquake produced clusters of aftershocks (M_W ≤ 6.4) up to 80 km from the fault rupture and up to 100 km beyond the end of the rupture. Because the mainshock occurred far from the nearest plate boundary and the nearest recorded earthquake, it is unusually isolated from the stress perturbations caused by other earthquakes, making it a good candidate for stress transfer analysis despite the absence of near-field observations. We tested whether the off-fault aftershocks lie in regions brought closer to Coulomb failure by the main rupture. We evaluated four published source models for the main rupture. In fourteen tests using different aftershocks sets and allowing the rupture sources to be shifted within their uncertainties, 6 were significant at ≥ 99% confidence, 3 at > 95% confidence, and 5 were not significant (< 95% level). For the 9 successful tests, the stress at the site of the aftershocks was typically increased by 1-2 bars (0.1-0.2 MPa). Thus the Antarctic plate event, together with the 1992 M_W=7.3 Landers and its M_W=6.5 Big Bear aftershock 40 km from the main fault, supply evidence that small stress changes might indeed trigger large earthquakes far from the main fault rupture.