Coastal hazard assessment and mapping in Northern Campania, Italy

In the Northern Campanian coastal zone, over 150 km long, three geomorphic units are recognised: (1) sandy beaches that are well developed in the northern area, where a prominent river mouth (Volturno River) is also present; (2) steep and rocky shores, often with gravelly beaches or debris cones at their base, are mainly diffuse in the southern area (Sorrentine Peninsula); and, lastly, (3) “techno coast”, shorelines stabilized with revetments and seawalls as well as former natural environments no longer clearly operational because of urbanization, as is visible in Naples and in the Vesuvian coast. Six primary hazards are considered in this investigation: shoreline erosion, riverine flooding, storms, landslides, seismicity and volcanism, and man-made structures. These hazards do not have a uniform distribution along this coast in terms of their frequency and intensity; moreover both their interaction and the intensive action of humans, often uncontrolled, makes it difficult to assess the overall coastal hazard. In this paper a semi-quantitative method with which to quantify, rank and map the distribution of hazard is applied along this particular stretch of coast. In such a stretch, previously characterized in terms of types and processes and compartmentalized into geomorphic units, the effect of individual hazards, based on their magnitude and recurrence, is evaluated. Dominant and subordinate hazards for each geomorphic unit are identified, assigning a rank that is also a weighting. Comparison of each weighting through an interaction matrix permits the calculation of a resultant, which is the overall hazard assessment and which can be expressed cartographically. The results obtained for a coastal zone with one of the highest pressures from urbanization in the world, help us to recognise that this approach could become a useful tool to aid decision-making regarding coastal land-use and planning.     

Upper-crustal structure of the Benevento area (southern Italy): fault heterogeneities and potential for large earthquakes

The Benevento region is part of the southern Apennines seismogenic belt, which experienced large destructive seismic events both in historical and in recent times. The study area lies at the northern end of the Irpinia fault, which ruptured in 1980 with a M_s = 6.9 normal faulting event, which caused about 3000 casualties. The aims of this paper are to image lateral heterogeneities in the upper crust of the Benevento region, and to try to identify the fault segments that are expected to generate such large earthquakes. This work is motivated by the recognition that lithological heterogeneities along major fault zones, inferred from velocity anomalies, reflect the presence of fault patches that behave differently during large rupture episodes. In this paper, we define the crustal structure of the Benevento region by using the background seismicity recorded during 1991 and 1992 by a local seismic array. These data offer a unique opportunity to investigate the presence of structural discontinuities of a major seismogenic zone before the occurrence of the next large earthquake. The main result that we obtained is the delineation of two NW-trending high-velocity zones (HVZs) in the upper crust beneath the Matese limestone massif. These high velocities are interpreted as high-strength regions that extend for 30-40 km down to at least 12 km depth. The correspondence of these HVZs with the maximum intensity regions of historical earthquakes (1688 AD, 1805 AD) suggests that these anomalies delineate the extent of two fault segments of the southern Apenninic belt capable of generating M = 6.5⁻⁷ earthquakes. The lateral offset observed between the two segments from tomographic results and isoseismal areas is possibly related to transverse right-lateral faults.     

Quaternary normal faulting in southeastern Sicily (Italy):a seismic source for the 1693 large earthquake

We present geological and morphological data, combined with an analysis of seismic reflection lines across the Ionian offshore zone and information on historical earthquakes, in order to yield new constraints on active faulting in southeastern Sicily. This region, one of the most seismically active of the Mediterranean, is affected by WNW–ESE regional extension producing normal faulting of the southern edge of the Siculo–Calabrian rift zone. Our data describe two systems of Quaternary normal faults, characterized by different ages and related to distinct tectonic processes. The older NW–SE-trending normal fault segments developed up to ≈400  kyr ago and, striking perpendicular to the main front of the Maghrebian thrust belt, bound the small basins occurring along the eastern coast of the Hyblean Plateau. The younger fault system is represented by prominent NNW–SSE-trending normal fault segments and extends along the Ionian offshore zone following the NE–SW-trending Avola and Rosolini–Ispica normal faults. These faults are characterized by vertical slip rates of 0.7–3.3  mm  yr ⁻¹ and might be associated with the large seismic events of January 1693. We suggest that the main shock of the January 1693 earthquakes ( M ~ 7) could be related to a 45  km long normal fault with a right-lateral component of motion. A long-term net slip rate of about 3.7  mm  yr ⁻¹ is calculated, and a recurrence interval of about 550 ± 50  yr is proposed for large events similar to that of January 1693.     

Multifractal analysis of the spatial distribution of earthquakes in southern Italy

We evaluate the complete spectrum of the generalized fractal dimension of the spatial pattern of microearthquakes in Southern Italy, revealing a multifractal distribution structure. Our analysis is focused on the dependence of the multifractal distribution on the size of the selected area and the kind of seismicity in the area. As the size of the window varies, we observe that the capacity, information and correlation dimensions vary significantly, while both d _∞ and d _−infin; remain unchanged within their errors limits. We interpret this result in terms of the observation that our data are mainly clustered around a linear fault (the Sisifo fault). When we restrict the selected windows around the fault, clustering around a line (the fault) is highlighted. The capacity dimension changes from about 1.8 to about 1.4 and the correlation dimension decreases because we observe in detail the clustering of the seismicity along the fault, which approximates the maximum intense clustering of the whole data set. Although our results are strongly influenced by the fact that the data are dominated by the epicentres located on the fault, we can conclude that multifractal analysis can be a very useful tool to discriminate the seismicity linked to a particular fault in a given area.     

Source parameters of large historical (1918–1962) earthquakes, South Island, New Zealand

We present the results of body waveform modelling studies for 17 earthquakes of M _w ≥5.7 occurring in the South Island, New Zealand region between 1918 and 1962, including the 1929 M _s = 7.8 Buller earthquake, the largest earthquake to have occurred in the South Island this century. These studies confirm the concept of slip partitioning in the northern South Island between strike-slip faulting in southwestern Marlborough and reverse and strike-slip faulting in the Buller region, but indicate that the zone of reverse faulting is quite localized. In the central South Island, all historical earthquakes appear to be associated with strike-slip faulting, although recent (post-1991) reverse faulting events suggest that slip partitioning also occurs within this region. The difference between historical and recent seismicity in the central South Island may also reflect stress readjustment occurring in response to the 1717 ad rupture along the Alpine fault. Within the Fiordland region (southwestern South Island) none of the historical earthquakes appears to have occurred along the Australian/Pacific plate interface, but rather they are associated with complex deformation of the subducting plate as well as with deformation of the upper (Pacific) plate. Two earthquakes in the Puysegur Bank region south of the South Island suggest that strike-slip deformation east of the Puysegur Trench is playing a major role in the tectonics of the region.     

Factors underlying piping in the Basilicata region, southern Italy

Piping/tunnelling erosion is a widely spread process in the Plio-Pleistocene marine clays of the Basilicata region in southern Italy. The pipes are often closely concentrated along the surface drainage networks at different depths with a tunnel (length) and a diameter varying from just a few centimetres to some metres. The formation and evolution of pipes in the badlands can be explained through: (1) geo-structural characteristics of the clay, (2) material properties such as a high exchangeable sodium percentage, (3) favourable climatic conditions, and (4) hydraulic gradient along the path controlled by the gully or ravine bottom that is acting as a local drain. The exposure and the extension of joints at the surface and in the bedrock along the slope are the main factors required for development of the pipes. The absence of the piping erosion on the slopes, where a reasonably thick layer of the soil material covers the open joints, shows that although certain material properties and climatic conditions play an important role, they are not sufficient to develop extensive piping erosion in the area.