Eduardo García-Meléndez

An exceptionally long paleoseismic record of a slow-moving fault: The Alhama de Murcia fault (Eastern Betic shear zone, Spain)

Most catastrophic earthquakes occur along fast-moving faults, although some of them are triggered by slow-moving ones. Long paleoseismic histories are infrequent in the latter faults. Here, an exceptionally long paleoseismic record (more than 300 k.y.) of a slow-moving structure is presented for the southern tip of the Alhama de Murcia fault (Eastern Betic shear zone), which is characterized by morphological expression of current tectonic activity and by a lack of historical seismicity. At its tip, the fault divides into a splay with two main faults bounding the Gonar fault system. At this area, the condensed sedimentation and the distribution of the deformation in several structures provided us with more opportunities to obtain a complete paleoseismic record than at other segments of the fault. The tectonic deformation of the system was studied by an integrated structural, geomorphological, and paleoseismological approach. Stratigraphic and tectonic features at six paleoseismic trenches indicate that old alluvial units have been repeatedly folded and thrusted over younger ones along the different traces of the structure. The correlation of the event timing inferred for each of these trenches and the application of an improved protocol for the infrared stimulated luminescence (IRSL) dating of K-feldspar allowed us to constrain a paleoseismic record as old as 325 ka. We identified a minimum of six possible paleoearthquakes of M w = 6–7 and a maximum mean recurrence interval of 29 k.y. This provides compelling evidence for the underestimation of the seismic hazard in the region.

Neotectonics and Plio-Quaternary landscape development within the eastern Huércal-Overa Basin (Betic Cordilleras, southeast Spain)

Abstract The Huercal-Overa Basin is one of a series of Neogene sedimentary basins located within the Betic Cordillera of southeast Spain. Its geological and geomorphological history has been controlled by tectonic activity culminating in basin inversion during the Plio-Quaternary. Deformation of the Huercal-Overa Basin is associated with left-lateral strike-slip faulting in relation to its position within the Trans-Alboran shear zone. In this paper, we focus upon the eastern portion of the Huercal-Overa Basin and make the first attempt to reconstruct the long-term landscape development during the Plio-Quaternary. This is done through integration of geological and geomorphological data obtained through field observations and GIS and remote sensing techniques. In particular, this paper provides a case study that contributes to the understanding of landscape development within tectonically active shear zones. Within the eastern part of the Huercal-Overa Basin, the main tectonic activity is associated with the left-lateral strike-slip Lorca-Alhama fault (oriented NE–SW). During the Late Pliocene and Early Pleistocene, the interaction of this fault with older Miocene ENE–WSW to E–W orientated structures formed a subsiding area with pull-apart basin characteristics termed the Cubeta del Saltador. Subsidence within the Cubeta del Saltador enabled sedimentary infilling by braided rivers with sediment being derived from the Sierra de Las Estancias to the north and the Sierra de Almagro to the south. Sedimentary deformation has resulted in the development of a series of progressive unconformities, angular unconformities and faulting within the alluvial sediments. Towards the end of this stage of landscape development, an increase in tectonic activity resulted in the creation of elevated tectonic highs in the north (Alto de la Garita del Diablo) and east (Loma de Garcia) of the Cubeta del Saltador. From the middle Pleistocene onwards, a progressive decrease in tectonic activity is recorded. Alluvial sediments infilled the Cubeta del Saltador. These were dominated by braided river sediments that formed part of a fan-shaped alluvial distributary system derived from the Sierra de las Estancias to the north. In contrast, smaller debris-flow-dominated alluvial fans were derived from the Sierra de Almagro along the southern margin. Currently, the study area presents an asymmetric configuration, reflecting the different topographic characteristics of the northern and southern limiting mountain fronts.

Monitoring the Extent of Contamination from Acid Mine Drainage in the Iberian Pyrite Belt (SW Spain) Using Hyperspectral Imagery

Monitoring mine waste from sulfide deposits by hyperspectral remote sensing can be used to predict surface water quality by quantitatively estimating acid drainage and metal contamination on a yearly basis. In addition, analysis of the mineralogy of surface crusts rich in soluble salts can provide a record of annual humidity and temperature. In fact, temporal monitoring of salt efflorescence from mine wastes at a mine site in the Iberian Pyrite Belt (Huelva, Spain) has been achieved using hyperspectral airborne Hymap data. Furthermore, climate variability estimates are possible based on oxidation stages derived from well-known sequences of minerals, by tracing sulfide oxidation intensity using archive spectral libraries. Thus, airborne and spaceborne hyperspectral remote sensing data can be used to provide a short-term record of climate change, and represent a useful set of tools for assessing environmental geoindicators in semi-arid areas. Spectral and geomorphological indicators can be monitored on a regular basis through image processing, supported by field and laboratory spectral data. In fact, hyperspectral image analysis is one of the methods selected by the Joint Research Centre of the European Community (Ispra, Italy) to study abandoned mine sites, in order to assess the enforcement of the European Mine Waste Directive (2006/21/EC of the European Parliament and of the Council 15 March 2006) on the management of waste from extractive industries (Official Journal of the European Union, 11 April 2006). The pyrite belt in Andalucia has been selected as one of the core mission test sites for the PECOMINES II program (Cracow, November 2005), using imaging spectroscopy; and this technique is expected to be implemented as a monitoring tool by the Environmental Net of Andalucia (REDIAM, Junta de Andalucia, Spain).

Spectral identification of pyrite mud weathering products: a field and laboratory evaluation

Monitoring of mine waste on sulphide deposits through remote-sensing hyperspectral data contributes to the prediction of potential surface-water quality, quantitatively estimating acid drainage and metal contamination on a yearly basis. Based on previous Hymap mapping of salt efflorescence on mine wastes, various domains within the mine facilities (Iberian Pyrite Belt, Spain), selected because of their geomorphological setting, were sampled to conduct a laboratory experiment. Samples from mine-waste piles, pyrite mud tailings and river sediments were continuously exposed to the atmosphere during the summer, and spectral measurements were collected in the dark room on several days. The spectral response was monitored throughout the summer, when the pyrite oxidation process is active and the mineralogy on the surface changes continuously. The mineralogical identification capability of algorithms such as the Spectral Angle Mapper, Binary Encoding and Spectral Feature Fitting based on archive spectral libraries is discussed. Trends of mineral growth differ spectrally over time according to the geological setting. Subtle mineralogical changes are described using the spectral response and their meaning as indicators of pyrite oxidation intensity on mine-waste piles, pyrite mud tailings and river sediments. Therefore, sulphide mine-waste weathering products may be used as small-scale targets for a short-term record of climate variability, providing a useful tool to assess environmental geological indicators in semi-arid areas.

River acid mine drainage: sediment and water mapping through hyperspectral Hymap data

The Odiel River (Huelva, southwest Spain) carries acidic water originating from mine waste contamination, including massive sulphide ore deposits. As the river approaches the coastal estuary, tidal factors influence both sediment and water dynamics. As water velocity decreases, sediment load transport capacity also decreases, building river bars consisting of boulders upstream and sands downstream. Salt water near the estuary affects river water chemistry by neutralizing acidity derived from mine wastes. The occurrence of pyrite mud and hydrated iron sulphate efflorescence, precipitated from acidic waters, is plugged by marine water with chloride, which precipitates from the salt water. Hymap airborne hyperspectral data were used to evaluate tidal influence using spectral features. Grain size variations on river pebble bars, localized crusts of variably hydrated iron sulphate and oxides and cation exchange with chloride salts in the lower river segment as it enters the estuary were spectrally described and mapped. The presence of vegetation proved particularly problematic for the spectral identification of contamination products as well as the precise delineation of inundated areas along the river. The transition from dry to wet zones is the crucial challenge in using spectral imagery to identify and track contaminants in the river and along its flood plain. The use of a reference mineralogical spectral library, developed in the laboratory, requires a careful geological context evaluation to provide efficient environmental information on contamination parameters. Based on hyperspectral analyses of critical spectral features, river locations that may be a key for tracing significant, future contaminant fluctuations were identified.

Multisensor data integration and GIS analysis for Natural Hazard mapping in a semiarid area (southeast Spain)

Abstract Natural Hazards are mostly related to the actuation of active geomorphological-geological processes that condition landform development. The objective of this work is to evaluate a method to combine digital image processing techniques and GIS analysis in order to extract and classify the main terrain attributes that identify Natural Hazard prone areas and to improve the accuracy of the differentiated terrain mapping units. Synergism of multisensor data of different spectral and spatial resolutions (SPOT PAN and Landsat TM images), together with the use of a Digital Elevation Model for rectifying the multisensor data set and for relief quantification contribute to the delineation of terrain mapping units. Additionally, spatial frequency filtering is applied for the enhancement of geomorphological linear features, specially in those images with greater spatial resolution. The resultant integration of Remote Sensing imagery with conventional data (field work and thematic maps) in a GIS is an efficient tool for the assessment and mapping of Natural Hazards.

Pyrite mine waste and water mapping using Hymap and Hyperion hyperspectral data

Hyperspectral low spatial resolution Hyperion data are used to map mine waste from massive sulphide ore deposits, mostly abandoned, on the Iberian Pyrite Belt. Hymap high spatial resolution data are used for crossed interpretation. Mine dams, mill tailings and mine dumps in a variable state of pyrite oxidation are recognizable. Ponds of acid water in the mine sites are spectrally outstanding and, with simple image processing procedures, mappable. In addition, acid water with different chemical composition is mappable with hyperspectral data, whether of high or low spatial resolution. A sequence of hyperspectral image processing algorithms used to produce the maps is suggested. Therefore, hyperspectral data are invaluable in giving quick hints on the quality of the rapidly changing state of the contamination generated by sulphide mine waste, enabling the authorities to activate mitigation procedures.

Mapping spatial variations of iron oxide by-product minerals from EO-1 Hyperion

This study aimed to map mine waste piles and iron oxide by-product minerals from an Earth Observing 1 (EO-1) Hyperion data set that covers an abandoned mine in southwest Spain. This was achieved by a procedure involving data pre-processing, atmospheric calibration, data post-processing, and image classification. In several steps, the noise and artefacts in the spectral and spatial domains of the EO-1 Hyperion data set were removed. These steps include the following: (1) angular shift, which was used to translate time sequential data into a spatial domain; (2) along-track de-striping to remove the vertical stripes from the data set; and (3) reducing the cross-track low-frequency spectral effect (smile). The Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) algorithm in combination with the radiance transfer code MODTRAN4 was applied for quantification and removal of the atmospheric affect and retrieval of the surface reflectance. The data set was post-processed (filtering, spectral polishing) in order to remove the negative values and noise that were produced as the a result of de-striping and atmospheric calibration. The Mahalanobis distance algorithm is used to differentiate the area covered by mine piles from other main land-use classes. The spatial variations of iron oxide and carbonate minerals within the mine area were mapped using the Spectral Feature Fitting (SFF) algorithm. The pre-processing of the data and atmospheric correction were vital and played a major role on the quality of the final output. The results indicate that the vertical stripes can be removed rather well by the local algorithm compared to the global method and that the FLAASH algorithm for atmospheric correction produces better results than the empirical line algorithm. The results also showed that the method developed for correcting angular shifts has the advantage of keeping the original pixel values since it does not require re-sampling. The classification results showed that the mine waste deposits can be easily mapped using available standard algorithms such as Mahalanobis Distance. The results obtained from the SFF method suggest that there is an abundance of different minerals such as alunite, copiapite, ferrihydrite, goethite, jarosite, and gypsum within the mine area. From a total number of 754 pixels that cover the mine area, 43 pixels were classified as sulphide and carbonate minerals and 711 pixels remained unclassified, showing no abundance of any dominant mineral within the area presented by these pixels.

Monitoring acidic water in a polluted river with hyperspectral remote sensing (HyMap)

Abstract Sulphide mine waste extensively contaminates the Odiel River (southwest Spain), releasing sulphuric acid into the water body. Acidic water in this river precipitates and dissolves variably hydrated iron sulphate in a complex geological pattern controlled by climate. Local abrupt changes in the water pH in the vicinity of highly contaminated tributaries can be mapped by means of imaging spectroscopy using hyperspectral remote sensing (HyMap) data. Also, increased pH through mixing of acidic river water with marine water can be detected when the river reaches the area influenced by sea tides. Mapping the quality of water with hyperspectral data is confounded by vegetation, either dry or wet, rooted or floating. The spectral features of acidic water measured with a field spectrometer revealed the spectral influence of green vegetation, similar to the influence of the depth and transparency of water. Careful mapping of such parameters with HyMap data must therefore precede any spectral evaluation of water related to acidity in a river course. The spectral features detectable by HyMap data and associated with pH changes caused by contamination in river water by iron sulphide mine waste, and their controls, are described and references established for routine monitoring through hyperspectral image processing.

Estimating altitude in distribution records of Amphibians and Reptiles: a comparative study between topographic maps and Remote Sensing data

Altitude is an important factor when explaining species distributions. However, many biogeographical studies register altitude directly through topographic maps; a time-consuming manual process prone to mistakes. Currently, GIS and DEMs allow this work to be done more efficiently. Two methods for registering altitude for locations of amphibians and reptiles in the Iberian Peninsula were compared in order to evaluate their efficiency and similarity: manually through topographic maps, and automatically with a GIS, where two DEMs were analysed: the SRTM DEM and a DEM generated through topographic maps. The SRTM altitudes were similar to those recorded by the manual method (only Rana perezi presented differences), whereas the other DEM had differences in almost all amphibians and three reptiles. The differences between both DEMs corresponded mostly to rivers and band effect of radar sensor. The GIS method was faster, efficient and no time was consumed in searching and correcting human errors.