Science Study Pinpoints Active Fault Tied To Central Europe's Worst Earthquake And Predicts Seismic Pattern

The study--completed by researchers with ETH Zurich, the University of Basel in Switzerland, and the University of Strasbourg in France--finally pinpoints the exact source of the devastating 1356 Basel earthquake. It also suggests a time-frame for when the next major earthquake may strike Basel.

An active fault, marked at ground-level by a ridge or escarpment called a fault scarp, has caused three successive ruptures, moving the Earth's surface upward by 1.8 meters (about 6 feet), over the past 8,500 years, researchers discovered.

Basel may not suffer a massive earthquake in this century, said Peter Huggenberger of the University of Basel, a co-author on the study. But, the presence of nuclear and chemical industry in the area means that any seismic activity could threaten public safety. And, according to governmental and insurance estimates, an earthquake similar to the 1356 event would cause an estimated 30 to 50 billion U.S. dollars worth of damage (50 to 80 billion Swiss francs), added co-author Domenico Giardini of ETH Zurich.

The Science study describes a consistent pattern of seismic activity that "points to a recurrence time for a 1356-type earthquake in the Basel area of about 1,500 to 2,500 years," explained lead author Mustapha Meghraoui of the University of Strasbourg.

Though researchers emphasized that they can't predict the next major earthquake with certainty, the seismic pattern they identified would give the region time to safeguard infrastructure and fine-tune emergency procedures. "We need to take precautionary measures now," Giardini said.

Basel--renowned as a Renaissance city of artistic and intellectual rebirth at the intersection of Switzerland, France and Germany--suffered catastrophic losses during the 1356 earthquake. According to historical accounts, a first quake struck "at the dinner time," around 7:00 pm on 18 October 1356, setting the stage for a second, stronger event "at the bed time," probably about 10:00 pm. Some 30 to 40 medieval castles collapsed in the hardest hit area. Many more churches and towers toppled within a 200-kilometer radius of Basel, as the earthquake reached a Mercalli intensity of IX to X, comparable to the disaster in Izmit, West Turkey, two years ago.

Beginning near the Swiss Jura Mountains south of Basel, the fault scarp covers at least eight kilometers, or nearly five miles. It extends in a northeasterly direction through a rift valley south of the Rhine River (the Rhine graben), traversing the flat fields of the Birs Valley to reach the city's southern edge. Indeed, scientists said, it's possible that the fault extends even farther north across the city, and deeper south, into the Jura Mountains. The Basel-Reinach fault is part of a larger "seismogenic layer."

Finding the precise source of the 1356 Basel earthquake has been difficult: The fault is partly obscured by dense Alpine forests, and seismic activity in the region is so infrequent that researchers can't easily determine the fault's location.

To more fully characterize the Basel-Reinach fault, scientists first studied the deformations it has caused at ground level--including ancient meanders from the