SH-wave seismic reflection at a landslide (Patigno, NW Italy) integrated with P-wave

The aim of this paper is to present the acquisition and processing up to the depth migrated section of an SH-wave reflection seismic profile. This experience is conducted on a deep-seated gravitational slope deformation located in the Northern Apennines in Italy. The SH-wave depth-migrated image in the investigated area provides a detailed description of the small reactivation slip surfaces delineating minor landslides at shallow depths, which are responsible for the major damages observed. These results are integrated with a recently acquired P-wave seismic reflection profile investigating the same slope and delineating the highly deformed layer at depth, liable for the deep-seated gravitational slope deformation. The combined use of P-waves and SH-waves allows to gain a deeper knowledge of the landslide internal setting that is necessary to mitigate the risk associated with the mass movement

High-resolution coherency functionals for improving the velocity analysis of ground-penetrating radar data

We aim at verifying whether the use of high-resolution coherency functionals could improve the signal-to-noise ratio (S/N) of Ground-Penetrating Radar data by introducing a variable and precisely picked velocity field in the migration process. After carrying out tests on synthetic data to schematically simulate the problem, assessing the types of functionals most suitable for GPR data analysis, we estimated a varying velocity field relative to a real dataset. This dataset was acquired in an archaeological area where an excavation after a GPR survey made it possible to define the position, type, and composition of the detected targets. Two functionals, the Complex Matched Coherency Measure and the Complex Matched Analysis, turned out to be effective in computing coherency maps characterized by high-resolution and strong noise rejection, where velocity picking can be done with high precision. By using the 2D velocity field thus obtained, migration algorithms performed better than in the case of constant or 1D velocity field, with satisfactory collapsing of the diffracted events and moving of the reflected energy in the correct position. The varying velocity field was estimated on different lines and used to migrate all the GPR profiles composing the survey covering the entire archaeological area. The time slices built with the migrated profiles resulted in a higher S/N than those obtained from non-migrated or migrated at constant velocity GPR profiles. The improvements are inherent to the resolution, continuity, and energy content of linear reflective areas. On the basis of our experience, we can state that the use of high-resolution coherency functionals leads to migrated GPR profiles with a high-grade of hyperbolas focusing. These profiles favor better imaging of the targets of interest, thereby allowing for a more reliable interpretation

Early to late Holocene vegetation and fire dynamics at the treeline in the Maritime Alps

We used pollen, plant macrofossil, and charcoal records to investigate local long-term timberline shifts and changes in vegetation composition in relation to fire activity at the modern upper forest limit (ca. 2,000 m a.s.l.) in the Mont Bégo area, Maritime Alps of France and Italy. The area is an important place for Alpine archaeology because it has thousands rock-art carvings whose age cannot be directly assessed. Our new record confirms the occurrence of distinct land use phases (7,450–7,150, 6,200–4,900, and 4,250–3,700 cal bp), as suggested by earlier studies of rock art typology. Moreover, the vegetation reconstruction from macrofossils, with co-dominance of Pinus and Betula, suggests that early Holocene conditions were moister than in drier inner Alpine valleys, where Larix decidua played a more important role, both in the past as well as in modern timberline forests. After 8,000 cal bp, the timberline shifted upwards and mixed Abies alba and Pinus cembra stands established around the study site. These fire sensitive trees were finally replaced during the Bronze Age (around 4,000 cal bp) by L. decidua, which still dominates the subalpine woodlands in the area today. Our study supports the notion that while the range of A. alba has been reduced at the colder end of its natural distribution, that of L. decidua has been widened by land use changes and fire disturbances to create high alpine wood pastures

SH-wave reflection seismic survey at the Patigno landslide: integration with a previously acquired P-wave seismic profile

Seismic investigation on landslide is hampered by several factors that could prevent the use of the reflection seismic method to characterize the subsurface architecture (Jongmans and Garambois, 2007). Moreover, acquisition and processing of reflection seismic data are more time consuming compared with other geophysical techniques such as refraction seismic and electrical resistivity tomography (ERT), leading inevitably to higher costs. Notwithstanding these difficulties, recently some attempts to delineate the deep slip surface of large landslides have been carried out using P-wave reflection seismic surveys (Apuani et al., 2012; Stucchi and Mazzotti, 2009; Stucchi et al., 2014;). P-wave reflection seismic method is effective in imaging the slip surface at a depth sufficiently greater than the seismic wavelength, whereas, for very shallow horizons, it suffers from the limited resolution that can be obtained by the use of compressional waves. In this regards, SH-waves can be used to overcome this limitation (Deidda and Balia, 2001; Guy, 2006; Pugin et al., 2006,), but they require a specifically-designed energy source for waves generation, geophones measuring horizontal components of particles motion and an accurate choice of acquisition parameters. On the contrary, due to attenuation, the depth of investigation for SHwaves can be lower than for P-waves (Pugin et al., 2006). Therefore the geological understanding of a mass movement can take advantage of a combined use of both these geophysical methodologies. This is the case of the Patigno landslide, a great landslide located in the upper basin of Magra River, in the Northern Appennines, Italy (Fig.1), where a P-wave study carried out in the last years (Stucchi et al., 2014) was able to image the deepest discontinuity of the landslide body at around 40-50 m depth, but no description of the shallower layers can be inferred. Because these surface layers are the slip surfaces of quick reactivation movements of the landslide, an SH high-resolution reflection seismic survey was planned along the previous P-wave profile (Fig.1). This new survey associated to the P-wave investigation allows a more robust description of the landslide body, from the deepest discontinuity up to the very shallow portions of the landslide. This work describes the planning, acquisition and processing of the SH reflection seismic survey, and also gives a possible combined interpretation of both P and SH seismic images

Temperatures recorded by cosmogenic noble gases since the last glacial maximum in the Maritime Alps

While proxy records have been used to reconstruct late Quaternary climate parameters throughout the European Alps, our knowledge of deglacial climate conditions in the Maritime Alps is limited. Here, we report temperatures recorded by a new and independent geochemical technique—cosmogenic noble gas paleothermometry—in the Maritime Alps since the last glacial maximum. We measured cosmogenic 3He in quartz from boulders in nested moraines in the Gesso Valley, Italy. Paired with cosmogenic 10Be measurements and 3He diffusion experiments on quartz from the same boulders, the cosmogenic 3He abundances record the temperatures these boulders experienced during their exposure. We calculate effective diffusion temperatures (EDTs) over the last ~22 ka ranging from 8°C to 25°C. These EDTs, which are functionally related to, but greater than, mean ambient temperatures, are consistent with temperatures inferred from other proxies in nearby Alpine regions and those predicted by a transient general circulation model. In detail, however, we also find different EDTs for boulders from the same moraines, thus limiting our ability to interpret these temperatures. We explore possible causes for these intra-moraine discrepancies, including variations in radiative heating, our treatment of complex helium diffusion, uncertainties in our grain size analyses, and unaccounted-for erosion or cosmogenic inheritance

Sand supply from shoreface to foredunes: aeolian transport measurements and morphological evolution of a Tuscany beach stretch (Italy)

The coastal dunes are a highly dynamic sedimentary environment characterized by a continuous time-space readjustment in terms of morphology, shape and dimension. This is mainly due to the periodic fluctuation of the volume of sand available and by the force of the deflation processes, which are in turn driven by the interplay among pattern of vegetation cover, surface roughness and local-regional wind regime. The aim of our research is to quantify the deflation, transport and deposition of sands in a natural coastal field dune system located in the northern coast of Tuscany, Italy. The northern part of the investigated area is characterized by stable coastline condition while southwards strong erosive processes took place since 1800 year. Sedimentological data come from a series of sand collectors spaced along transects orthogonal to the coastline from the backshore to the semi stable dune field. The collectors were constructed of PVC pipe 100 x height 10 cm, with two openings 7 cm wide and 50 cm tall arranged on opposite sides of the tube. Opening willing to windward served for sand collection, and to leeward, covered with a metal wire 60μm opening. Collectors were buried along, until the base of the free window coincide with the surface of the ground about 1,5 m. The sand trapped within each collector was sampled every two hours for three consecutive times. In laboratory sand samples were weighed and subject to grain size analysis by means of mechanical sieves. The local winds parameters and their fluctuation with the time were acquired through a Meteorological mobile station. The station is equipped with three ammeters located to three different heights from ground surface: 40, 120 and 180 cm. A wireless sensor allows the constant output of data (each 5 sec) to a device. Temperature, and relative humidity value are furnished every 30 minutes. Analysis of data has evidenced the time-space fluctuation of sand volume in the two study area (stable area and under erosion). Basing on this methodological approach the time-space fluctuation of sand volume experienced by the two study areas (stable area and under erosion) has been estimated

Geomorphologic Map of Northeastern Sector of San Jorge Gulf (Chubut, Argentina)

This paper presents a 1:100,000 scale geomorphologic map of the Northeastern sector of San Jorge Gulf (Chubut Province) in Patagonia, Argentina, covering more than 1,000 km2. Derived from remote sensing data and validated by three field surveys, it has been compiled in order to understand the past and recent evolution of the area with particular reference to sea-level oscillation studies, for which this map is the basic tool. The very low human impact and rates of dynamic landscape change allow the preservation of extensive palaeo deposits and landforms, including those indicative of sea-level variations. The relative change of sea level dominates landscape evolution, allowing the formation of widespread marine and lagoon deposits often interfingering with fluvial deposits and reworked by aeolian process in the framework of consequent beach progradation

Atmospheric dynamics over Europe during the Younger Dryas revealed by palaeoglaciers

A dataset of 120 palaeoglaciers ranging from Morocco in the south to Svalbard in the north and from Ireland in the west to Turkey in the east, has been assembled from the literature. A robust quality control on the chronology was undertaken and, when derived from cosmogenic nuclides, ages were recalculated using the most up-to-date production rates. All the reconstructed glaciers date to the Younger Dryas. Frontal moraines/limits were used to initiate the palaeoglacier reconstructions using GlaRe, a GIS tool which generates an equilibrium profile ice surface along a single flowline and extrapolates this to out to a 3D ice surface. From the resulting glacier surfaces palaeo-ELAs were calculated within the GIS. Where multiple glaciers were reconstructed within in a region, a single ELA value was generated. Results show that ELAs decrease with latitude but have a more complex pattern with longitude. A database of 121 sites, spanning the same geographical range as the palaeoglaciers, was compiled for Younger Dryas temperature, determined from palaeoproxies, for example pollen, diatoms, coleoptera, chironimids etc. These proxy data were merged and interpolated to generate maps of average temperature for the warmest and coldest months and annual average temperature. Results show that, in general, temperature decreases with latitude. Temperature at the palaeo-ELAs were determined from the temperature maps using a lapse rate of 0.65C/100m and the precipitation required for equilibrium was calculated. Positive precipitation anomalies are found along much of the western seaboard of Europe, with the most striking positive anomalies present in the eastern Mediterranean. Negative precipitation anomalies appear on the northern side of the Alps. This pattern is interpreted to represent a southward displaced polar frontal jet stream with a concomitant track of Atlantic midlatitude depressions, leading to more frequent incursions of low pressure systems especially over the relatively warm eastern Mediterranean, enhancing cyclogenesis. This is similar to the modern Scandinavia (SCAND) pattern which, in its positive phase, is characterised by a high pressure anomaly over Fennoscandia and western Russia, negative pressure anomalies around the Iberian Peninsula and enhanced cyclogenesis in the central and eastern Mediterranean. During the YD the Fennoscandian Ice Sheet and permafrost across much of northern continental Europe and Russia would have generated a high pressure region leading to a persistent, enhanced SCAND circulation

MAPPA cores: an interdisciplinary approach

In the urban and periurban area of Pisa, 18 cores ranging in depth between 7 and 15 m were performed and analysed through an interdisciplinary approach, which led to an improved stratigraphic log representation. The acquired data also improved our knowledge about the palaeoenvironmental and human settlement evolution of Pisa area over the past 6000 years, evidencing the mutual interaction existing between landscape and human activities