The predawn earthquake that occurred on Friday, centered in southern Illinois, has reminded people that the Midwest region is threatened as much as other earthquake prone areas of the country.

The 5.2 magnitude earthquake, which had hit at 4:36 am, was felt on an area of about 120.000 square miles from Nebraska to Atlanta, but its center was just outside West Salem in southeastern Illinois, which is a mostly rural region of small cities, sitting over the Wabash fault zone. Fortunately, the quake did not damage too much and nobody was seriously hurt.

The quake shook mostly nerves, as people are not used to them and the probability that it would occur in this region are rather small in comparison to California or other seismic active areas in the country.

While the fault zones under the Mississippi River Valley have caused some of the most powerful recent quakes east of the Rockies, a region covered with old buildings not built to withstand seismic activity, scientists say that they know to little about the Midwest seismic area.

They said that their situation is very different of California’s, where the tectonic plates beneath the Earth's surface collide, as they found it extremely difficult to find out the causes of earthquakes in the area.

The earthquake’s most likely origin was in what geologists call the Ozark Dome region, an area that covers around five Southern and Midwestern states and includes several active fault lines.

However, scientists were confused on Friday, not knowing exactly which fault had triggered the tremor. While the seismic zones of the Western states are mostly studied and known, the Midwest is largely uncharted territory.