Image: Map of the region surrounding Memphis, TN. Darker orange area is covered by think sediments called the Mississippi embayment, that affect how the ground shakes during earthquakes. White lines indicate likely locations of faults, and black dots show the locations of earthquakes since the mid-1970s. (Credit: CERI)
Story: The New Madrid Fault may have seen its day and the Wabash Fault is the new kid on the block. The Illinois earthquake registered 5.2 on the Richter scale and hit at 4:40 a.m. with a strong aftershock occurring at approximately 10:15 a.m. that morning, followed by lesser ones in subsequent days. The U.S. Geological Survey has counted more than 20 aftershocks following Friday's tremor. The initial earthquake was felt in parts of 16 states. "A lot of the attention has been on the New Madrid Fault, but the Wabash Valley Fault could be the more dangerous one, at least for St. Louis and Illinois...There hasn't been a magnitude 6 earthquake on the New Madrid zone in more than 100 years, yet in 20 years there have been three magnitude 5 or better earthquakes on the Wabash Valley Fault." Recent re-analysis of data by the USGS shows that the New Madrid fault risk is much less than was thought three decades ago. The three notable earthquakes that occurred at the end of 1811 and the beginning of 1812 were not magnitude 8s, but rather magnitude 7s. A magnitude 8 is 30 times more energetic than a magnitude 7. "The damage to the region by those earthquakes has been exaggerated. St. Louis was here at the time, and all that happened was some chimneys fell in East St. Louis." There are some precursory phenomena that have been observed right before some earthquakes. Radon or helium gas may leak out of the ground as the ground cracks. Sometimes water well pressure changes, or there's a change in the magnetic field. Electrical resistivity changes have been noted, too. These are changes we can measure with instruments, but we can't sense them as humans.
More Quakes Rumble Off Oregon Coast
Another series of earthquakes added to the geological mystery off the Oregon Coast on Monday. Four sizable quakes rumbled off the coastline in a span of four hours Monday night. The largest, a 4.1 earthquake located 115 miles west of Port Orford, occurred at 7:17 p.m. Over the past several weeks, there have been hundreds of small quakes west of the coastal towns of Bandon and Port Orford. They have varied in magnitude from 3.0 to above 5.0. Scientists have said they don't know exactly what the earthquakes mean, but they could be caused by molten rock rumbling away from the recognized faults off Oregon.
Nature has a way of continually surprising us and inspiring awe within us, and it seems there are just as many fantastical wonders t...