by Alessandra Cardone
ROME, Oct. 30 (Xinhua) -- The earth in central Italy could still tremble for weeks or months, after a latest quake, and the strongest so far, struck early on Sunday, an Italian scientist said.
"We expect temblors in the affected areas to keep going on in the next days and weeks, possibly with a slow decreasing intensity," Warner Marzocchi, chief scientist of the National Institute of Volcanology and Seismology (INGV), told Xinhua in an interview.
A 6.5-magnitude earthquake hit at some 5.5 km from central Italy's Norcia town, a famous medieval town in the Umbria region, at 07:40 a.m. local time (0640 GMT) on Sunday.
It caused no victims, according to the civil protection agency. However, it was the most powerful quake affecting the country since 1980, and almost flattened some important historic buildings, including the 14th-century San Benedetto Basilica in Norcia.
The quake hit four days after two other powerful events of magnitude 5.4 and 5.9, respectively, which had struck on Oct. 26. Furthermore, a previous 6.0-magnitude quake had hit the same central region on Aug. 24, killing 298 people.
All these events were somehow related, and the domino effect might continue even for months, the expert warned.
"I think people (in central Italy) will keep feeling the seismic activity for weeks, and even months," Marzocchi said.
He added the sequence of strong temblors close to each other in time and space did not surprise him.
"The August's 6.0 quake caused a disturbance in the balance between the fault lines distributed along the central Apennine mountain chain, which are close to each other," Marzocchi explained.
The distress is distributed across neighbouring fault lines on the earth's crust, possibly bringing some of them to break when the strain accumulated becomes excessive.
"Adjacent faults, involved but not activated by a strong previous event, can at a certain time unleash the tension built up on them, causing a new quake. This is probably what has happened," the chief seismologist said.
Such phenomenon was registered several times in other quakes in Italy and around the world. It was also a reason why experts could not rule out the chance of another major event.
"Earthquakes tend to move, or migrate, in clusters, which means several aftershocks or new temblors can follow a major one. Such clusters become clearer after a large quake, and the events that follow can be milder, but also stronger than the first," he said.
As examples, Marzocchi recalled central Italy in 1703, and the northeast Friuli region in 1976: in both cases, devastating quakes hit at a distance of few weeks or months from one another.
The expert further explained Sunday's 6.5-magnitude quake, as well as all other events since Aug. 24, were "typical" for that territory, which is crossed by the Apennines and considered at high-seismic risk.
"The Apennines are subjected to a sort of 'stretching' activity. The Adriatic ridge tends to move toward the northeast, while the Tyrrhenian ridge is more stationary, or tends towards the opposite direction," he said.
Because of this, the mountainous chain was being pulled apart by this "splitting tension."
"This is why the ground beneath the quake-affected areas sank about 15-20 cm, as we could detect from satellite images," the INGV chief scientist said.
