Search

This paper both describes and discusses landslides and other ground effects induced by the September–October 1997 seismic sequence, which struck the Umbria and Marche regions (Central Italy). Three main events occurred on 26 September at 00:33 and 09:40 GMT, and 14 October with magnitude M w equal to 5.8, 6.0 and 5.4, respectively; furthermore hundreds of minor but significant events were also recorded. The authors examined an area of some 700 km 2 around the epicentre (Colfiorito). Primary and secondary effects were observed, including surface faulting phenomena, landslides, ground fractures, compaction and various hydrological phenomena. Surface evidence of faulting reactivation was found along the well-known capable faults, to a total length of ca. 30 km. Landslides, which were the most recurrent among the phenomena induced, consisted mainly of rock falls and subordinately of rotational and translational slides, which were generally mobilised by the inertia forces during the seismic motion. The percentage of reactivated old landslides decreased as the distance from the epicentral zone increased; a similar decrease had been observed for the 1980 Irpinia earthquake (Southern Italy). The ground fracture distribution was consistent with the regional structural setting and the general pattern of macroseismic field. Numerous episodes of hydrological changes were observed within the most severely damaged area. All this evidence confirms the relevance of the study of ground surface effects for achieving a more complete evaluation of seismic hazard.

The Campanian province has a rich history of human interaction with volcanic eruptions. In a region currently inhabited by 3 million people, it is crucial to have precise and accurate geochemical characterization of volcanic units within the region so as to identify the spatial distribution of past events. Furthermore, tephrochronology is becoming an important tool in the region for correlating past environmental records. Unfortunately, many of the key units have been geochemically analysed using relatively imprecise methods, making correlation problematic. Although robust correlations have been established in the Campanian province using a range of methods, including stratigraphy and geochronology, more distal correlation requires precise geochemical characterisation of individual glass shards. Here we report major oxide data, geochemically characterising 17 key tephra units within the Campanian province using wavelength dispersive spectrometry (WDS). The new data confirm the trachytic nature of most of the eruptions. To effect more precise correlations between units (especially in distal locations), proximal units must be individually analysed for major oxides using WDS on the vitreous phase, and statistically analysed for robust correlations. In cases where similar geochemistry exists, analysis of trace and rare earth elements may be necessary.

The eruption's first surge instantly killed some people sheltering from the impact. The town of Herculaneum, lying at the foot of Mount Vesuvius on a cliff overlooking the sea, was buried by a succession of pyroclastic surges and flows (currents of volcanic ash and hot gases generated by collapse of the eruptive column) during the plinian eruption of ad 79. The skeletons of 80 of 300 people who had taken refuge in 12 boat chambers along the beach have now been unearthed from the first surge deposit. We have investigated how these people were killed by this surge, despite being sheltered from direct impact, after its abrupt collapse (emplacement) at about 500 °C on the beach. The victims' postures indicate that they died instantly, suggesting that the cause of death was thermally induced fulminant shock1 and not suffocation, which is believed to have killed many of the inhabitants of Pompeii and of Herculaneum itself.