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 l ess than or equal to 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 t he nearest plate boundary and the nearest recorded earthquake, it is unusua lly isolated from the stress perturbations caused by other earthquakes, mak ing it a good candidate for stress transfer analysis despite the absence of near-field observations. We tested whether the off-fault aftershocks lie i n regions brought closer to Coulomb failure by the main rupture. We evaluat ed four published source models for the main rupture. In fourteen tests usi ng different aftershocks sets and allowing the rupture sources to be shifte d within their uncertainties, 6 were significant at greater than or equal t o 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 aftershoc ks was typically increased by 1-2 bars (0.1-0.2 MPa). Thus the Antarctic pl ate 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 cha nges might indeed trigger large earthquakes far from the main fault rupture .