EL CERRITO, Feb. 16 (AScribe Newswire) -- Calif., U.S. and Italian geophysicists have discovered that Rome's ancient structures are vulnerable to a wider range of earthquake hazards than previously believed, according to research published in the latest issue of the Bulletin of the Seismological Society of America, the journal of the world's premier earthquake-research organization.
After building the first-ever 3-D computer model of the historic city's underground geology, the international team modeled two types of earthquakes that have struck Rome in the past. They discovered that some earthquakes are likely to cause ground shaking in central Rome that will last up to one minute -- much longer than earlier 2-D models indicated.
The conclusion: Rome's 2000-plus-year-old buildings are in danger of crumbling when a temblor of magnitude 7 or larger strikes.
At least 20 large earthquakes have damaged Rome in the past 2,000 years; the most recent occurred in 1915. Earthquakes that affect Rome originate in two places: the nearby volcanic Alban Hills, about 25 km away, which typically generate tremors with magnitudes as large as 5; and the more distant Central Apennines, about 100 km away, which are the source of earthquakes as large as magnitude 7.
A newer city, like San Francisco or Los Angeles, would roll better with the punch from a large quake, said Kim Olsen, the principal author of the paper, "3-D Ground-Motion Estimation in Rome, Italy," with co-authors Aybige Akinci, Antonio Rovelli, Fabrizio Marra, and Luca Malagnini, all geophysicists at the Istituto Nazionale di Geofisica e Vulcanologia in Rome.
"But ancient Rome is an aching city," Olsen said. "It is so beat up from millenia of wear and tear. This research is important because it indicates where we can expect the largest ground shaking, and it shows that the duration of the ground shaking is likely to be longer than previously estimated."
"The duration of ground motion induced by an earthquake is critical because historic Rome is built on the soft, unconsolidated sediments of the Tiber River. These sediments form a complex 3-D weave beneath the city, creating great variability over short distances in Rome's subsurface geology."
Olsen and his Italian colleagues used data from more than 1,000 boreholes to constrain their 3-D model of subsurface Rome. They used the model to predict ground shaking from two scenarios: one of a magnitude 5 earthquake originating in the Alban Hills district and another of magnitude 7 originating in the Central Apennines.
Some of the predicted shaking patterns -- those with the highest resolution -- agree quite well with areas where ancient structures, such the Aurelian Column, show damage from previous earthquakes. The modeling study forecasts the strongest shaking inside the alluvial sediments deposited by the Tiber River, particularly along the boundaries.
But unexpectedly, the geophysicists also found that an earthquake from the more-distant Central Apennine source causes much longer duration of ground motion than an Alban Hills quake.
This is because the geology between the Central Apennines and the ancient city acts as a wave guide, directing and amplifying seismic waves into the city. The seismic waves thus modeled forecast up to one minute of roller-coaster-like ground shaking in central Rome, much longer than the duration predicted by previous simplified models.
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CONTACTS: Dr. Kim Olsen, San Diego State University, kbolsen@sciences.sdsu.edu, 619-594-2649
Mary George, SSA Media Relations, press@seismosoc.org/303-666-4288
ABOUT SSA: The Seismological Society of America (SSA) is a
scientific society devoted to the advancement of earthquake
science. Founded in 1906 in San Francisco, the Society has
members throughout the world representing a variety of
technical interests: seismologists and other geophysicists,
geologists, engineers, insurers, and policy-makers in
preparedness and safety.
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