A group of Japanese architectural and construction experts visited the city of L'Aquila shortly after a 6.3-magnitude earthquake devastated the central region of Italy on April 6 to investigate the scale of the damage.

The strong earthquake hit L'Aquila, about 100 km northeast of Rome, as well as surrounding towns. The quake killed more than 290 people, injured over 1,000 and damaged or destroyed some 10,000 buildings, according to a report by the investigation group, which was in the area from April 18 to 21.

The earthquake mainly damaged brick structures but also hit reinforced-concrete buildings made in the modern era as well as historically important structures, according to the report.

Ichizo Kishimoto, an associate professor at Osaka University who joined the research and headed the group's architectural team, said the damage was rather serious for a city with a high geographic risk of earthquakes.

"There are a number of constructions that are vulnerable to tremors in L'Aquila. Once buildings with such structures collapse, the scale of damage tends to be huge," he said in a recent telephone interview.

Kishimoto said the damage was so severe because many conventional constructions were made of stones and soil with brick walls. But modern buildings did not escape the devastation.

Iron reinforcing rods (rebars) inside pillars and girders had rusted, and become vulnerable to earthquakes.

That was because the concrete around the bars was too thin and they were often visible sticking out of the concrete, when the concrete should have been at least 3 cm thick to protect them, Kishimoto said.

The team was comprised of 10 professionals, most of them university scholars and members of four Japanese academic societies that study earthquakes — the Architectural Institute of Japan, Japan Association for Earthquake Engineering, Japanese Geotechnical Society and Japan Society of Civil Engineers.