Multidisciplinary investigations on the Roman aqueduct of Grumentum (Basilicata, Southern Italy)

The Romans built the ancient town of Grumentum during the 3rd century B.C. in the southern part of the Agri
 high Valley (Basilicata Region, Southern Italy) near the confluence of the Sciaura stream in the Agri River.
 Now it is one of the most important archaeological sites of Southern Italy. In fact, after a period of wars in
 this area between Romans and Carthaginians, a great deal of restoration was started in 57 B.C. These works
 affected the city walls, public buildings and finally endowed the Roman colony with important infrastructures,
 such as the new aqueduct. In this work, we attempt to reconstruct the ancient layout of the Roman aqueduct
 of Grumentum. As a starting point, we followed some descriptions from the 19th century, when the structure
 was still well preserved. Then, we performed a multidisciplinary geophysical approach to the best preserved
 remains of the aqueduct. In particular, the geophysical investigation started with the use of a portable GPS allowing
 us to acquire the co-ordinates of the outcropping rests of the ancient structure. Then, we used an optical
 pumping magnetometer to perform seven gradiometric maps over a broad area of about 8000 m2. From
 the literature descriptions, dating to the first part of the 19th century, we can deduce that the state of preservation
 of the Roman aqueduct was much better than the present one. Thus we can hypothesise as the cause of
 its fast involution the fact that it was located in the epicentral area of the large destructive earthquake which
 occurred in the Basilicata Region in 1857 (Mallet, 1862). To this aim, we performed a first attempt to correlate
 the state of preservation of the aqueduct remains with the local seismic amplification by means of the
 HVSR (Horizontal to Vertical Spectral Ratio) technique. This survey allowed us to obtain the site amplification
 spectra along the aqueduct layout and assess the fundamental vibration frequency of the investigated
 structure. The possibility of landslides was ruled out by a careful geological survey. The relationship between
 aqueduct path and damage should then be attributed to closeness to earthquake seismogenic fault