RESEARCHERS LOOK TO RIVER COURSE, RUINS IN ITALIAN VALLEY FOR CLUES TO PREVIOUS EARTHQUAKES

FAYETTEVILLE, Ark. - Earthquakes in northern Italy have caused the loss of lives and homes. Researchers seeking to better understand the geologic processes behind these earthquakes have turned to new sources of information on historic faults: water and archeology.

University of Arkansas geosciences professor Margaret Guccione and her colleagues Marco Pizziolo, Rafaelle Pignone, Luigi Piccardi and Dario Delle Donne studied a region on the Po Plain north of the Italian Appennine Mountains, focusing on the path of the Secchia and Panaro Rivers that flow from the mountains onto the plain. Guccione presented their findings at a recent meeting of the Geological Society of America.

"The conventional wisdom is that the earthquakes are concentrated in the Appennine Mountains but that the Po Plain is not very tectonically active at the moment," said Guccione. "But we believe there is still some tectonic activity in that area and historic earthquakes in the Po Plain that support our hypothesis." The site of earthquake activity has important implications for people who live in the mountains and plains.

Guccione, who has studied possible faults along the Mississippi River Basin, sought a similar site for exploration. The Secchia and Panaro Rivers that she and her colleagues studied flow onto a portion of the Po Plain near Modena, home of balsamic vinegar and Ferraris.

Rivers that flow from mountains onto plains typically flow directly away from the mountain front and form an alluvial fan. But the Secchia and Panaro Rivers, about 25 miles apart, do not follow this pattern. In the Appennine Mountains and on the Po Plain adjacent to the mountain front, the rivers run parallel to one another. But away from the mountain front they turn and flow towards one another until they are about three miles apart. Then they turn again and flow parallel to each other.

"It’s opposite what you would normally expect," said Guccione.

The cause of the rivers’ unusual behavior appears to be a depression in the middle of the territory between the two rivers with a difference in elevation of about 25-30 feet. Guccione and her colleagues used radiocarbon dating to examine the history of sediment cores taken from the edges of the depression. The sediment core dates indicate that the depression did not exist prior to 21,000 years ago.

As the rivers flow into the depression, they bring sand and mud to fill it. Dates from the cores indicate that the depression has been filling rapidly in geologic timeat the rate of about five feet every 1,000 years—but it is not completely filled yet. The sedimentation can obscure historic faults and other evidence of earthquakes, so the researchers looked for other evidence that might point to earthquakes and deformation on the Po Plain such as the age and distribution of archeological sites.

Two thousand years ago, ancient Roman farmers created their fields in a grid pattern, and in high areas where sediment has not buried the fields, modern farms still use this pattern. A Bronze Age site that dates back about 3,500 years is only buried by a foot of sediment in the same area.

However, in the depression near Modena, no archeological sites have been found. The sites have either been buried deeply or no people lived in the swampy area because the ground was too poorly drained to cultivate. The distribution of archeological sites suggests that there is historic evidence of deformation in the earth’s surface, and this deformation could be associated with earthquakes, Guccione said.