Croatia’s government has begun to repair sinkholes that have pocked a farming region near the capital, prompting panic from villagers who have watched them grow – in number and size.

The sinkholes made a dramatic appearance in early January, less than a week after a magnitude 6.4 earthquake hit central Croatia on December 29 last year, killing seven people.

Prompting headlines around the world, including references to “Swiss cheese”, about 100 sinkholes showed up around the towns of Mecencani and Borojevici, southeast of the capital, Zagreb.

The largest sinkholes measured nearly 30 metres (98 feet) across.

The “bumper crop” of sinkholes is unusual in that earthquakes and other seismic events do not usually cause them. However, in areas where groundwater has eroded the bedrock below to a point where it can no longer support the soil above, sinkholes do appear.

Stjepan Terzic, a chief engineer at Croatia’s national geological survey, said that while sinkholes are a normal phenomenon, the high concentration of them “in such a small location” is unusual, but that the shocks caused by the earthquake had accelerated their appearance.

“Thus in a short period of time, numerous holes have emerged for which, in normal conditions, decades if not longer periods would be needed,” he told AFP news agency.

Seismologist Josip Stipčević, from the Department of Geophysics at the University of Zagreb, told Total Croatia News the earthquakes the country experiences are the result of the movement of the tectonic plates below the surface, with the large Eurasian Plate colliding with the smaller Adriatic Plate – a fragment of the larger African Plate.

Since the beginning of the 20th century, Croatia has experienced nine earthquakes with a magnitude greater than 6.

The repairs to fill in the sinkholes started last week and are expected to last a month and a half.