An anomalous increase of seismicity was recorded at intermediate distances from the Landers, California, earthquake of 28 June 1992 (M = 7.3). Several authors have suggested that enhanced activity was triggered at distances of up to 17 fault lengths. We test a 90-year catalog of shallow world earthquakes (M > 7) for evidence of this effect. It is found that triggering is present even at these high magnitude levels. The pattern of enhanced activity comprises two concentric regions: (a) the aftershock region and (b) the region of triggered seismicity at distances of 300 to 1000 km. The two regions are activated together; they are separated by a ring-shaped gap at a distance of around 300 km. This “Mexican Hat” pattern is attributed to recovery flows generated by the stress drop of the earthquake in a steady-state convecting system.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.