A series of four major earthquakes struck Central Italy between Abruzzo, Lazio, the Marche and Umbria regions on 18 January 2017.
Arbus is a "comune" (municipality) in the Province of South Sardinia in the Italian region of Sardinia.
 Located in the southwest coast of the island, Arbus is known for its coastline, the Costa Verde, and for several archeological sites, such as the mines of Montevecchio.
 With an area of 267 km² , Arbus is the second largest municipality in Sardinia.
Filadelfia (Greek: Philadelphia ) is a "comune" (municipality) in the Province of Vibo Valentia in the Italian region Calabria, located about 30 km southwest of Catanzaro and about 20 km northeast of Vibo Valentia.
 The city was built in 1783 by the people of Castelmonardo, on land that was 6 km from their city that was destroyed by an earthquake.
 As of 31 December 2013, it had a population of 5,500 and an area of 30 km2 .
Cautano is a "comune" (municipality) constituted from two countries, Cautano and Cacciano, in the Province of Benevento( until 1861 Province of Avellino) in the Italian region Campania, located about 75 km northeast of Naples and about 13 km west of Benevento and about 13 km north of Montesarchio.
 .
 As of 31 December 2004, it had a population of 2,191 and an area of 19.7 km².
Piz Badile (3,308 m) is a mountain of the Bregaglia range in the Swiss canton of Graubünden and the Italian region of Lombardy, the border between the two countries running along the summit ridge.
 Its north-east face, overlooking the Swiss Val Bregaglia near Soglio, is considered one of the six great north faces of the Alps.
Umbria ( ; ] ), is a region of central Italy.
 It is the only Italian region having neither a coastline nor a border with other countries.
 It includes the Lake Trasimeno, Marmore's Falls, and is crossed by the River Tiber.
 The regional capital is Perugia.
 Umbria is known for its landscapes, traditions, history, culinary delights, artistic legacy, and influence on culture.
Casamicciola Terme is a "comune" (municipality) in the Metropolitan City of Naples in the Italian region Campania, located in the northern part of the Ischia Island.
 On August 21, 2017 was hit by a 4,3 Mb earthquake, causing damage to some houses and 2 fatalities.
Longitarsus vilis is a species of beetle in the subfamily Galerucinae that is can be found on Canary Islands, in such European countries as Portugal, Spain, and also on Italian islands such as Sardinia and Sicily and the Italian mainland.
 It can also be found in African countries such as Algeria and Morocco and is also common in Italian region of Calabria.
San Martino d'Agri is a hill town and "comune" in the province of Potenza, in the Southern Italian region of Basilicata.
 It is a town of less the 800 people most of the year, but in August the population swells to around 2,000 when "Sammartinesi" return for the "Festa della Madonna della Rupe", some coming from as far as North America and South America.
 San Martino d'Agri is on the peak of a hill at 666 meters above sea level.
 At one point in the town's history, there was a major mudslide ("frana") that wiped out most of the town; however, it recovered.
 Atop the hill stands a medieval castle, which was first owned by the "barone".
 However, after the "barone" was overthrown, there was an earthquake that destroyed much of the town.
 The castle was later renovated and divided up into sections for different families' housing.
 In the late mid-1900s, a section was abandoned and wasn't renovated until 2003.
 That part, as well as another is currently owned and still being renovated.

Question: When did the earthquake strike the only Italian region having neither a coastline nor a boarder with other countries?
Answer: 18 January 2017