Ground motion phenomena in Caltanissetta (Italy) investigated by InSAR and geological data integration

Urban areas are frequently affected by ground instabilities of various origins. The location of urban zones affected by ground instability phenomena is crucially important for hazard mitigation policies. Satellite-based Interferometric Synthetic Aperture Radar (InSAR) has demonstrated its remarkable capability to detect and quantify ground and building motion in urban areas, especially since the development of Advanced Differential Interferometric SAR techniques (A-DInSAR). In fact, the high density of reflectors like buildings and infrastructures in urban areas improves the quality of the InSAR signal, allowing sub-centimetric displacements to be reliably detected. The A-DInSAR techniques allow urban zones affected by ground deformation to be located and mapped, but clearly they are not able to point out the causes of the instability phenomena. These can only be highlighted by an integrated analysis of multidisciplinary data, like geological, geotechnical, SAR interferometric and historical data. The overlay of these data, which is possible within a Geographic Information System (GIS), is a useful tool to identify ground motion phenomena affecting urban zones. In this study we apply this kind of approach to Caltanissetta, a provincial capital in Sicily (Italy), where local damage has been detected. The reconstruction of the local near-surface geology shows the presence of zones affected by local natural hazard factors, essentially due to the local presence of soils with poor mechanical properties or swelling soils, high topographic gradients and steep slopes on loose soils. Processing 17 ASAR-ENVISAT SAR images covering the time interval October 2002–December 2005 by means of an A-DInSAR procedure, the Caltanissetta deformation map has been realized. It shows that most of the city is stable, with the exception of three zones, situated in the northwestern, northeastern and southern parts of the city, respectively. Two of them, characterized by high topographic gradients and steep slopes on sandy soils, are affected by subsidence ground motion. An uplift motion is recognized in the other zone, characterized by the local presence of expansible clays. Geotechnical swelling tests carried out on them have shown a swelling behavior. On site surveys have highlighted the presence of damage in the zones affected by ground motion.     

Influence of the North Atlantic Oscillation (NAO) on climatic factors and estuarine water temperature on the Basque coast (Bay of Biscay): Comparative analysis of three seasonal NAO indices

The effect of the North Atlantic Oscillation (NAO) indices on climatic conditions and their subsequent influence on water temperature of two Basque estuaries (estuary of Bilbao and estuary of Urdaibai) were assessed by transfer function (TF) models for the period 1997–2006. Results showed that air temperature had an immediate (lag=0) and significant negative response to the NAO, whereas rainfall was not correlated with this climate index. The negative correlation between NAO and air temperature was found to be stronger with the seasonal indices derived from the differences in surface pressure between Iceland and Azores than with that derived from the principal component time-series of the leading eigenvector of the sea-level pressure in an Atlantic sector. The correlations between rainfall and river discharge, and between air temperature and water temperature were positive and highly significant in both estuaries. The response of water temperature to air temperature was immediate in both estuaries, whereas one-quarter lagged responses were also observed in the estuary of Bilbao, which is deeper and more stratified than the estuary of Urdaibai. Our study provides evidence that on the Basque coast the NAO plays an important role in climate variations, which in turn affect estuarine water temperature.     

On the onset and meridional propagation of the ionospheric F2-region response to geomagnetic storms

The meridional propagation velocities of the ionospheric F2-region response to 268 geomagnetic storms are calculated. Ionospheric vertical sounding data of 1 h time resolution from several stations located in a longitude sector approximately centred along the great circle that contains both the geomagnetic poles and the geographic poles are used.Most meridional propagation velocities from high to low latitudes are less than 600 m/s. The smaller velocities are typical of global neutral meridional wind circulation and the larger are representative of traveling atmospheric disturbances.Simultaneous disturbances at several locations are more frequent during positive phases than during negative phases. Negative phase meridional propagation velocities associated with meridional neutral winds are less frequent in the southern hemisphere when compared with corresponding velocities observed in the northern hemisphere. This may be related to the fact that the distance between the geomagnetic pole and the equator is smaller in the northern hemisphere.Most negative phase onsets are within the 06–10 LT interval. For middle geomagnetic latitudes a “forbidden time interval” between 11 and 14 LT is present. The positive phase onsets show the “dusk effect”.     

Response of Acartia populations to environmental variability and effects of invasive congenerics in the estuary of Bilbao, Bay of Biscay

The effect of environmental factors (river discharge, water temperature and dissolved oxygen saturation) on the abundance and distribution of Acartia populations and the interactions between their congenerics was evaluated by means of transfer function (TF) models in the estuary of Bilbao during the period 1998–2005. The recorded species were Acartia clausi, Acartia tonsa, Acartia margalefi and Acartia discaudata. Acartia clausi dominated in the entire euhaline region of this estuary until 2003 when it was displaced from the inner part by A. tonsa. This invasive species (A. tonsa) was found for the first time in 2001 and colonized successfully the inner (salinity 30) and intermediate (salinity 33) waters of this estuary since 2003. The TF models revealed an immediate and negative effect of A. tonsa on A. clausi in the intermediate salinity (33) waters, where these species showed the highest spatial overlap. The results indicate that environmental changes from 2003 influenced the abundance of Acartia species, being unfavourable for A. clausi. The decrease of A. clausi abundance in low salinity waters was related to a significant decrease of dissolved oxygen saturation levels, whereas the increase of temperature was linked to a significant increase of A. tonsa. Acartia margalefi and A. discaudata were scarce over the entire period, but they were found to be valuable indicators of hydrological changes, which were associated to climate factors. These two latter species increased in abundance and expanded their seasonal distribution, and in the case of A. margalefi also its spatial distribution, in 2002, coinciding with the period in the time-series when autumn–winter rainfall and summer temperatures were lowest, and dissolved oxygen saturation levels were highest.