Unexpected earthquakes within continenal plates pose challenges

Unexpected earthquakes within continental plates pose challenges
Earthquakes that occur on "passive" continental margins, such as the August 2011 magnitude 5.8 Mineral, Virginia, earthquake, surprise people because they expect earthquakes to occur only on plate boundaries. But, in fact, large and damaging intraplate earthquakes occur fairly regularly on passive margins around the world. For instance, in North America the approximately magnitude 7 Charleston earthquake shook South Carolina in 1886, causing severe damage and about 60 deaths, and the 1929 magnitude 7.2 earthquake on the Grand Banks of Newfoundland, Canada, caused a tsunami, a large landslide, and 28 fatalities.