Weak quakes hit along county line
Staff writer
A pair of earthquakes hit early Monday along the county line east of Marion, but their magnitude was too weak to cause damage or to be felt by most people.
Both were centered half a mile north of 220th Rd. and half to a full mile east of Clover Rd.
The first struck at 5:02 a.m. and measured 2.5 on the Richter scale — the weakest magnitude typically felt by nearby residents.
The second struck six minutes later and measured slightly less powerful at magnitude 2.4.
They were the second and third earthquakes registered this month in the county. A previous quake, measuring 2.1, hit at 3:17 a.m. April 3. It was centered near 310th and Old Mill Rds.
So far this year, the county has experienced seven other earthquakes, none more powerful than this week’s.
Most have been near where Monday’s quakes were located. Four other quakes also have registered since Jan. 1 less than a mile east of there in Chase County.
Experts at Kansas Geological Survey, which has seismic monitoring equipment throughout the county, say the quakes are attributable not to oil well drilling, as stronger quakes in Oklahoma are, but to geological forces related to formation of the Flint Hills.
The western edge of what’s known as the Nemaha uplift skirts along the eastern part of the county from near Burdick to near Peabody and continues on, running north and south, across the state.
To date, no quakes in Marion County have ever reached magnitude 3. That’s the level at which visible shaking of objects occurs.
Each increment of one on the scale represents a tenfold increase in ground movement, so Monday’s 2.5-magnitude quake was one-fifth as powerful as one that might have shaken objects.
Quakes causing significant damage typically measure at least 5.5 on the scale. That’s 1,000 times more powerful that the quakes that struck here Monday.
Marion County’s quakes generally occur when harder rock such as granite, well beneath the limestone common in the area, cracks.
Rather than be felt, some quakes along the uplift are heard, sounding somewhat like a thunder clap or an explosion. The sound is literally that of rock breaking.
Although no area is safe from earthquakes, scientists generally agree that the Nemaha uplift poses little to no danger to county residents but remains an interesting geological phenomenon.