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With more than 6,400 aftershocks recorded in the first 6 months of the M7.8 Simeonof Earthquake aftershock sequence, we're still watching it closely. The largest aftershock in the sequence occurred on October 19, 2020. It was magnitude 7.6 earthquake and produced a vigorous aftershock sequence of it's own. The map below shows the distribution of the M7.8 mainshock, M7.6, M6.1, and M6.0 aftershocks as black stars and the remaining aftershocks in red. The aftershock zone extends over an area of 200 km long and 100 km wide (about 120 by 60 miles). The rupture patches of historical large events in the region are shown with the initial aftershock based rupture patch for the M7.8 mainshock. The M7.6 aftershock rupture originated outside the initial estimated rupture patch. More research is needed to better understand the interplay between these two large events.

The plot below shows the cumulative count of events with time on the left and magnitude of events with time for the earthquakes mapped above.

We will update these pages as the sequence unfolds.

Last Modified: February 10, 2021