Jose Delgado

Engineering-geological model of the Segura River flood plain (SE Spain): a case study for engineering planning

This article presents a sedimentological and geotechnical study of the surficial sediments in the Segura River valley (SE Spain). We formulate an engineering-geological model consisting of four zones, each characterized by its geotechnical properties and by various geotechnical problems (namely low bearing capacity, significant ground settlement and liquefaction of sandy sediments). The model quantifies the geotechnical properties and potential problems in each zone. It serves as a useful tool for preliminary geotechnical investigations. The model also enables a better design of field surveys as well as optimal selection of geotechnical investigation techniques for future civil engineering works.

Formate Adsorption onto Thin Films of Rutile TiO2 Nanorods and Nanowires

We evaluate the applicability of silicon prisms to infrared (IR) spectroscopic investigations of the oxide/electrolyte interface in the attenuated total reflection (ATR) configuration. Using formic acid as a probe adsorbate, a comparison is done between a rutile nanowire film supported on Si and a rutile nanorod film supported on ZnSe. The nanowires were 2 nm in diameter and were deposited directly on Si by chemical bath deposition, whereas the nanorods were deposited on ZnSe by solution casting of an aqueous dispersion prepared from a commercial powder. The lower penetration depth of the evanescent wave for silicon was compensated by a higher internal surface area of the corresponding nanowire film. Advantageously, much higher solution concentrations can be used in the case of the Si prism without a significant contribution of solution species to the IR spectrum. Furthermore, the high chemical stability of Si opens up the possibility of performing experiments in highly acidic aqueous solutions. Upon formate adsorption at pH 3.5, a pair of intense IR bands was observed in the wavenumber range where antisymmetric v(as)(COO) vibrations are expected, namely at 1537 and 1592 cm(-1) on nanorod films and at 1544 and 1586 cm(-1) on nanowire films. The relative band intensities are different for nanorod and nanowire films. While the bands at 1537/1544 cm(-1) are assigned to formate adsorbed on the (110) face, forming the bridging bidentate (mu) structure, those at 1592/1586 cm(-1) are tentatively attributed to formate adsorbed at low coordination adsorption sites at the nanocrystal edges. Bands corresponding to the carboxylate symmetric stretching and the HCO deformation were also observed.

DInSAR monitoring of land subsidence in Orihuela City, Spain: Comparison with geotechnical data

An advanced DInSAR technique called Coherent Pixels Technique (CPT) has been used to measure the subsidence existing in Orihuela city (Spain) during the period 1993-2001 due to ground water level fall. The estimated subsidence, with values lower than 7 cm, is highly influenced by soil geotechnical conditions like the deformable soil thickness. In addition, the wells location is an important subsidence factor because they are directly related to a decrease of the piezometric level.

Sea cliffs resulting from late Miocene extensional tectonics: the Serra Gelada case study (Betic Cordillera, Spain)

The Serra Gelada sea cliffs are carved in Mesozoic carbonate rocks belonging to the External Zones of the eastern Betic Cordillera (Alicante, SE Spain). Several normal faults with vertical slips of more than a hundred metres have played an important role in the origin of this coastline. Some previous studies propose that the present cliff morphology was mainly originated by Quaternary fault activity. However, the integration of geomorphological features, stratigraphical and sedimentological data, together with the results of the tectonic analysis of fractures occurring in Serra Gelada, and a detailed study of seismic reflection profiles carried out in the adjacent continental shelf, indicate that these normal faults were active mainly during the late Miocene. Therefore, the Serra Gelada sea cliffs represent a tectonically controlled long-term landscape. Thus, normal faults have not significantly modified the Serra Gelada relief since then. Furthermore, the northern part of the Serra Gelada cliff may be considered as an inherited pre-Quaternary relict palaeocliff since it has only undergone very little erosive recession.

Enabling SAR data exploitation by processing on-demand

Since many years the ESA Research and Service Support (RSS) service provides resources to support Earth Observation (EO) data exploitation. Significant value has been delivered in these years to EO researchers in terms of cost, time and resource saving, thus enabling enhanced scientific productivity. In the new Sentinel era, recently started with the launch of Sentinel-1 in April 2014, data volume and processing requirements will be more challenging than before. The EO scientific community accessing and using RSS resources will therefore experience even greater benefits in terms of cost, time and resources savings, for activities related to data procurement, handling, storage, access, and processing.

Towards a global flood frequency map from SAR data

The main objective of this study is to generate inundation maps of past flood events based on an archive of Synthetic Aperture Radar (SAR) data. Within a hierarchical image splitting framework, the flood mapping algorithm uses a histogram thresholding operation and a region growing process to delineate the flood extent. This algorithm is applied to an archive of SAR images in order to generate a flood frequency map. We define the flood frequency of a specific area as the ratio between the number of images where the area was detected as flooded and the total number of images within the employed data collection. SAR water-like ambiguities (e.g. urban areas, crops or shadow regions) are filtered out using auxiliary data sources such as the Height Above Nearest Drainage (HAND) index or land cover maps. The proposed methodology is applied to an ENVISAT ASAR image archive over the UK area. Results presented in this article demonstrate the effectiveness of this methodology.

Seismic-Induced Landslides: Lessons Learned from Recent Earthquakes in Spain

On February 23, 2015, an earthquake of magnitude Mw 4.7 (Imax = V, scale EMS) struck the center of the Spain, triggering dozens of instabilities in taluses and natural slopes of an area characterized by low relief. These instabilities were characterized by: (1) very small size, most of them with volumes lower than 1 m3, and (2) to occur in rock masses affected by multiple discontinuities, which pre-defined blocks that fell down during the shaking. The inventory of instabilities of this earthquake has shown that most of the instabilities occurred on the slopes of the road network, although the larger instabilities were observed in natural slopes. The comparative analysis of this inventory with those made for other recent earthquakes occurred in the SE of Spain (1999, 2002, 2005 and 2011), all of them of similar magnitude Mw (between 4.7 and 5.1), allow to recognize that the vast majority of instabilities induced by these earthquakes were rock/soil falls, being other typologies of landslides very rare. In all cases, the size of instabilities triggered were small, usually with volumes of 1 m3 or less, reaching the larger volumes up to 500–1000 m3. Data available from these events point out that large landslides, as known in relation with historical earthquakes in Spain, cannot be induced by moderate to low magnitude earthquakes. Besides, slope morphology seems to control the location of induced instabilities. Thus, when the terrain is steep, as in the area affected by the earthquake in Lorca (2011, Mw 5.1), most of instabilities occur in natural slopes and affect the upper part of slopes. As the relief is less rugged, natural slopes instabilities are progressively less frequent until the extreme case of the 2015 event, when instabilities were located mostly on slopes of the road network.

Diezma Landslide (Southern Spain): Geological Model and Seismic Response

The Diezma landslide (Southern Spain) occurred on March 18 of 2001 after a heavy rainfall period, interrupting an important motorway. Landslide involves a heterogeneous soil laying on a metamorphic substratum (shale). A geological model has been made using 34 boreholes drilled between 1998 and 2012 in this area. As it results from this model, the landslide mechanism is mainly controlled by a complex system of tear faults which dislodge a main thrust line. Since the landslide is located in a high seismicity area, it is of interest to know its seismic response. Ambient noise was measured within and around the landslide and the Nakamura’s method was applied for studying local seismic response. The obtained results show that: (i) the landslide mass is characterized by a clear seismic response respect to the surrounding stable areas, and (ii) a relation seems to exist between the frequency of peak amplitudes retrieved by Nakamura’s method and thickness of landslide mass in the mid-upper part of landslide body.

The high damaging mw 5.1 lorca 2011 earthquake: Possible role of local seismic amplification

On May 11, 2011, a seismic series struck the city of Lorca (SE Spain) causing widespread damage and 9 fatalities. The series was characterized by a Mw 4.5 foreshock occurred at 15:05 (GMT), a main event occurred at 16:47, Mw 5.1, and many other aftershocks of smaller magnitude. All focuses were shallow and located about 3 km N of this city. The acceleration records of both Mw 4.5 and 5.1 events at the station located at Lorca (LOR) show that main direction of the motion was almost perpendicular to the strike of the north segment of the Lorca fault (N50oE). To understand the local seismic response of the city area in general, and of the LOR site in particular, ambient noise and Vs30 was measured through the city and the whole set of accelerograms recorded at LOR was analyzed (period 1993–2013; epicentral distances from 2 to 150 km). The HVSRs do not show a significant amplification while from the accelerograms recorded at LOR, a possible “fault effect” related to the near fault shaking, as well as to a “fault-zone” effect, i.e. due to the dynamic properties of the fault zone rocks with respect to the adjacent rock masses was recognized. These effects are only visible in the case of earthquake records whose epicenters are closer than 15 km (i.e. produced by the fault zone). Such effect combined with large accelerations that occurred may explain the damages produced by the main event.

Legislation as a Tool to Mitigate Mass Movements in Spain

According to the Ministry of Internal Affairs, in the 1990–2012 period, there have been 57 deaths in Spain due to mass movements. The economic losses were estimated at about €180 million each year. Some of these losses have been related to violating the laws and/or the lack of risk-focused land use planning. In accordance with the provisions set out by the 9/2006 Spanish Strategic Environmental Assessment Act, an Environmental Sustainability Report is compulsory and must include a natural hazards map, as it is set out by the national Land Act (2/2008 Royal Legislative Decree). Although there is no natural hazards legislation in Spain, there is some sectoral legislation on several natural hazards but it does not specifically refer to mass movements. Despite most of these codes are mandatory, they are not usually enforced. However, Spanish legislation requires compulsory natural hazards reports in some cases but, unfortunately, there are no guidelines on how to conduct these reports.