Unknown Arkansas Fault Can Trigger Magnitude 7 Earthquake - Recent Series Of Small Quakes

  Excerpt: A previously unknown fault in eastern Arkansas could trigger a magnitude 7 earthquake with an epicenter near a major natural gas pipeline, a scientist said Wednesday.

Haydar Al-Shukri, the director of the Arkansas Earthquake Center at the University of Arkansas at Little Rock, said the fault is separate from the New Madrid fault responsible for a series of quakes in 1811-12 that caused the Mississippi River to flow backward.

Acres of cotton fields cover the fault west of Marianna, about 100 miles east of Little Rock, but stretches of fine sand mixed with fertile soil gave away the fault's location, Al-Shukri said. Liquefied sand bubbled up through cracks in the earth, while ground radar and digs showed vents that let the sand reach the surface, he said.

The fault, likely created in the last 5,000 years, sparked at least one magnitude 7 earthquake in its history. Such temblors cause massive destruction in their wake.

"This is a very, very dangerous (area) at risk of earthquake," Al-Shukri said. "When you talk about (magnitude) 7 and plus, this is going to be a major disaster."

Al-Shukri did not identify a time frame for the potential earthquake.

Such a quake would affect Little Rock and neighboring states such as Tennessee and Mississippi, Al-Shukri said.

Most Arkansas earthquakes occur in the state's northeast corner in the New Madrid Seismic Zone, but Al-Shukri said the Marianna fault was not connected because it was too far from the temblors caused by that zone.

During the winter of 1811 and 1812, a series of three earthquakes with magnitudes of around 8 struck the zone and much smaller temblors continue to hit today.

A series of quakes hit Arkansas in the last few days:

          MAG UTC DATE-TIME    LAT       LON   DEPTH  REGION
                                                                                    km

MAP 3.6  2010/10/11  16:06:04  35.315   -92.335     5.9    ARKANSAS
MAP 2.5  2010/10/11  13:43:31  35.292   -92.341    6.7     ARKANSAS
MAP 4.0  2010/10/11  13:33:40  35.304   -92.317    5.0    ARKANSAS
MAP 3.0  2010/10/10  12:48:22  35.322   -92.332    4.7    ARKANSAS
MAP 2.6  2010/10/09  13:45:33  35.297   -92.311    7.2    ARKANSAS
MAP 3.0  2010/10/09  04:13:40  35.307   -92.328   5.2    ARKANSAS
MAP 2.5  2010/10/07  23:20:34  35.309   -92.320   4.4   ARKANSAS

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