Bennett identified the fault using a technique called geodesy, which records the positions of rocks at a given time—similar to the way geographic positioning systems track people or objects.
Some of Bennett's colleagues in Croatia started taking geodetic measurements in 1994.
In 2005 and 2007 Bennett and his team repeated those measurements and began to realize that the ground motions had the telltale pattern of a thrust fault—a geologic feature where one plate moves up and over another.
"Then we started to put the pieces together," Bennett said.
"We recognized the long-term relationship between the fault and the islands and the mountains. It all began to make sense."
The team describes their results in the January issue of the journal Geology.
Chuck DeMets is a geologist at the University of Wisconsin, Madison, who was not involved with the study.
He noted that scientists already knew about the existence of multiple faults in Croatia.
"Bennett and his co-authors demonstrate that it is conceivable that a single master fault underlies these other faults and show that their data are adequately fit by this model," DeMets said.
"Additional observations may well show such a model to be overly simplistic, in which case the proposed master fault may not exist," he continued.
"However, they are already collecting additional data that will allow them to test their new model and possibly more complex models."
In the meantime, the new finding should be considered when gauging the region's earthquake and tsunami potential, the scientists suggest.
Previous calculations to assess these possibilities did not consider this fault to be active.
"We do not know, given the current data, whether or not the fault along which the motions take place is accumulating strain that will be released during a large future earthquake, or alternatively whether the strain is accommodated without earthquakes," study author Bennett said.
(Related news: "San Andreas Fault May Be Rare Quake 'Superhighway'" [August 16, 2007].)
"All indications are that the fault could produce a very large earthquake, but additional research is required to confirm this result," he said.
"If the fault is capable of producing very large earthquakes, it could also be capable of generating a tsunami, because the fault is underwater."
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