MEMPHIS, Tenn. — A magnitude 4.0 quake with an epi-center near Poplar Bluff, Missouri, rattled nerves as far south as Shelby County Wednesday night.

WREG spoke with a woman named Judith who is visiting Memphis from Idaho and was startled by Wednesday night’s earthquake.

“I was just in my hotel room, and I just felt a little bit of a shake, and I wondered,” Judith said. “Because I had experienced a earthquake about a year ago in Idaho, and that was really a little eerie.”

Gary Patterson is director of the Center for Earthquake Research and Information at the University of Memphis.

“We record about four hundred earthquakes per year in the New Madrid Seismic Zone,” Patterson said.

He showed us the graph of Wednesday night’s quake recorded at CERI in East Memphis.

“The first wave is the primary wave. It’s like a sound wave but it doesn’t do any damage. The damaging wave is the secondary wave, and you can see here the amplitude of the wave is much higher,” Patterson said.

He says a 4.0 quake can crack plaster and shake objects off shelves, but no damage has been reported in Memphis. He says not everyone in Memphis felt the quake unless if you were “still or at rest” when it hit.

But a look at the “Did you feel it?” map shows how many reports were filed and how large an area was affected.

“Stretching down from Memphis all the way up into St. Louis,” Patterson said. “So this is an area of over 90,000 square miles.”

Patterson says new broad band technology at CERI’s offices has long since replaced the old “drum type needle graph” and can more accurately pin point a quake’s location and magnitude, but public awareness and preparedness is key.

“An earthquake unfortunately occurs without warning. It’s not like a weather event,” Patterson said.

Patterson says an “after shock deployment team” could be traveling to the Poplar Bluff area in the next few days to set out high quality portable seismic instruments to learn more about the earthquake there.