january 1998

The only magnitude 8 or greater earthquake in the first half of 1998 happened in the Balleny Sea outside the Test area. It occurred about 250 km south of the Southeast Indian Ridge, some 500 km from the Antarctica cost and has the following parameters listed in the NEIC PDE: origin time 1998/03/25 03:12, latitude 62.88°S, longitude 149.53°E, depth 10 km, and Ms = 8.0 (MwHRV=8.3). Before this happened the area was generally recognized as aseismic. Enough to say that no earthquake was ever reported at distances less than 200 km from the March 25, 1998 main shock epicenter. The deficiency of seismic activity does not allow us to apply standard version of the algorithm here. However, a modified version of the M8 algorithm (set up for applications in lower rate seismic activity regions) would have distinguished the rise of activity at the junction of Southeast Indian and Macquarie Oceanic Ridges and predicted this earthquake (see Figure “Balleny 1998”).