April 2016 – LA CENTER, KY – An earthquake near La Center, Kentucky was felt in parts of Illinois and Missouri early on Sunday morning. According to the National Weather Service in Paducah and the USGS, a magnitude 3.5 was recorded about 8.7 miles north of La Center and 24.2 miles west of Paducah. It happened around 1:12 a.m. and had a depth of about 8.3 miles. People from Jackson, Mo., Grand Chain, Ill., Anna, Ill. and more have reported feeling it. –KFVS
The New Madrid Seismic Zone (NMSZ) is the most active seismic area in the United States east of the Rocky Mountains. The NMSZ is located in southeastern Missouri, northeastern Arkansas, western Tennessee, western Kentucky and southern Illinois. Southwestern Indiana and northwestern Mississippi are also close enough to receive significant shaking from large earthquakes occurring in the NMSZ.
The active faults in the NMSZ are poorly understood because they are not expressed at the ground surface where they can be easily studied. The faults are hidden beneath 100- to 200-foot thick layers of soft river deposited soils called alluvium. Fault scarps and traces in the soft alluvium erode in a very short time or may be rapidly covered by new deposits thereby quickly hiding evidence of earthquake fault lines. Faults in places like California, where rocks are at or near the ground surface, are much easier to study because the faults are readily found, seen, measured and analyzed.
Microseismic earthquakes (magnitude less than 1.0 to about 2.0), measured by seismographs but not felt by humans, occur on average every other day in the NMSZ (more than 200 per year). Active faults that have generated dangerous earthquakes in historic times or the recent geologic past (the last 10,000 years) are not always microseismically active. In fact, in some settings these quiet faults are considered the most dangerous ones because high built up stress has locked the two sides of the fault together thereby preventing the microseismic earthquakes. This is thought to happen as a prelude to a major rupture of the fault. It is not known if faults of this type exist in the NMSZ. If they do exist there is no easy way to locate them. –Missouri Geology