We have one every thirty some years. However, we're having magnetical changes and could get them more frequently and more severe.
I am not sure what you are referring to in regards to 'magnetical', but the time frames you mentioned are relatively accurate. The following except is out of date, but accurate for our purposes here.
Glade Spring-area historical tornado activity is significantly below Virginia state average. It is 66% smaller than the overall U.S. average.
On 4/4/1974, a category 3 (max. wind speeds 158-206 mph) tornado 6.2 miles away from the Glade Spring town center killed one person and injured 4 people and caused between $50,000 and $500,000 in damages.
On 1/25/1975, a category 2 (max. wind speeds 113-157 mph) tornado 0.7 miles away from the town center injured 2 people and caused between $5000 and $50,000 in damages.
Glade Spring-area historical earthquake activity is significantly above Virginia state average. It is 72% smaller than the overall U.S. average.
On 11/23/2006 at 10:42:57, a magnitude 4.3 (4.3 MB, 4.3 LG, Class: Light, Intensity: IV - V) earthquake occurred 27.7 miles away from the city center
On 11/2/2006 at 17:53:02, a magnitude 4.3 (4.3 MB, Depth: 0.6 mi) earthquake occurred 29.5 miles away from Glade Spring center
On 6/29/1996 at 19:30:42, a magnitude 4.1 (4.1 MB, 3.9 LG, Depth: 0.6 mi) earthquake occurred 29.1 miles away from the city center
On 10/26/1995 at 00:37:28, a magnitude 4.0 (3.9 MB, 4.0 LG, Depth: 0.6 mi) earthquake occurred 76.7 miles away from the city center
On 8/17/1990 at 21:01:17, a magnitude 4.0 (3.5 LG, 4.0 LG, Depth: 6.2 mi) earthquake occurred 86.8 miles away from Glade Spring center
On 4/19/1996 at 08:50:14, a magnitude 3.9 (3.9 MB, Class: Light, Intensity: II - III) earthquake occurred 70.1 miles away from the city center
Magnitude types: regional Lg-wave magnitude (LG), body-wave magnitude (MB)
The number of natural disasters in Washington County (12) is near the US average (12).
Major Disasters (Presidential) Declared: 9
Emergencies Declared: 3
Causes of natural disasters: Floods: 6, Storms: 5, Winter Storms: 2, Storm: 1, Blizzard: 1, Drought: 1, Flood: 1, Hurricane: 1, Ice Storm: 1 (Note: Some incidents may be assigned to more than one category).
Read more: http://www.city-data.com/city/Glade-Spring-Vi...