Chapter 4 Geophysical precursors at vesuvius from historical and archeological sources

Abstract

Abstract The Vesuvius area has been inhabited for several millennia and during this time several large and well-documented eruptions have occurred, but little is known about the earthquakes associated with these eruptions and no satisfactory correlation between macroseismic and instrumental parameters has been produced. Earthquakes have often been felt only in few towns at the foot of Vesuvius, and in incomplete historical reports sometimes only Naples is mentioned, the most important city in the area and 10km away from the volcano. From historical sources, little is known about the seismicity that preceded the eruption of 79 A.D. in spite of the earthquake of 62 A.D. which caused extensive damage in Pompeii and other towns around the volcano. This is evident from the ongoing excavations which show records of reconstruction and repair on walls, floors, plasters, mosaics and decorations. These excavations also show that before the eruption the water supply system in Pompeii was under repair and that the civic aqueduct was out of use and a new one being built. At that time, the Castellum Aquae water distribution system was not supplied by a regional aqueduct and water outlets were not connected with the civic piping network. This suggests that the town was experiencing difficulties from ground deformation for some time before the eruption, as attested by the historical record of seismic events. The seismic crisis preceding the eruption of 1631 is also poorly defined and can be characterized by a comparatively high-energy activity that was limited to several hours before the eruption, and probably by a minor activity that had been occurring for several months before the catastrophic event. The greatest pre-eruptive event can be rated at M ≤4. On 9 October 1999 an earthquake of significant magnitude ( M L =3.6) shook the Vesuvius area and considerable data from instrumental and macroseismic studies have been collected for the purpose of ascertaining the volcanic structure and pre-eruptive phase of Vesuvius. It appears that the seismic events at Vesuvius have always been of moderate energy, except for the earthquake of 62 A.D. whose energy was significant ( M =5). The earthquakes from 1631 to 1944 do not appear to cross the threshold of M =4.5, and the more recent seismicity has been maintained below M =4.