Possibilities of discriminating tropical secondary succession in Amazônia using hyperspectral and multiangular CHRIS/PROBA data

CHRIS/PROBA data collected in the Brazilian Amazônia in 4 view angles (−36°, nadir, +36°, +55°) and 62 bands (410–1000 nm range) were evaluated for the discrimination between primary forest and 3 stages of secondary succession after deforestation: initial (SS1; <5 years), intermediate (SS2; 5–15 years) and advanced (SS3; >15 years). Single view angle and multiangular approaches (nadir plus anisotropic information derived from reflectance ratios between view angles) were tested for discrimination. Both approaches used principal components analysis (PCA) applied to pixel spectra representative of each class in order to reduce data dimensionality at each dataset, to enhance separability between the classes, and to provide input variables for multiple discriminant analysis (MDA). The results showed that the off-nadir viewing improved discrimination between the successional stages. Discrimination between SS2 and SS3 was enhanced with PCA at +36° view angle. Primary forest and SS3 presented a more anisotropic behavior than SS2 and SS1, especially in the backward scattering direction (positive view angles) in which great amounts of sunlit canopy components were viewed by the sensor. MDA classification results showed that the multiangular approach produced an overall improvement in the discrimination. From the single (nadir) to the multiangular approach, classification accuracy using a separate set of pixels increased from 83.3% to 98.3% for SS1, 53.3% to 70.0% for SS2, and 58.3% to 76.7% for SS3. The nadir and multiangular classifications were statistically different at a 0.05% level of significance. Kappa statistics increased from 0.63 to 0.82. The results showed that multiangular data can improve the differentiation between primary forest and old stages of natural vegetation regrowth, which have been reported in the literature as the most difficult classes to be mapped in the Amazonian environment.     

Geological risk assessment by a fracture measurement procedure in an urban area of Zacatecas,Mexico

Natural Hazards - Geological hazards represent medium- and long-term risks, when they affect urban infrastructure and residential areas as they become a source of danger for the population. In...     

Mid-Holocene lateral collapse of Antuco volcano (Chile): debris avalanche deposit features,emplacement dynamics,and impacts

Antuco (37.4°S, 71.4°W; Chile) is a dominantly basaltic stratovolcano whose original?~?3300 m altitude main cone experienced a catastrophic sector collapse at?~?7.1 cal ka BP, producing a volcanic debris avalanche deposit (VDAD) with hummocky surface and?~?6.4 km³ of volume. We carried out geological studies of its debris avalanche deposit, which was distributed to the W and displays a longitudinal facies transformation from edifice’s megablocks and block to mixed facies in distal areas (up to 25 km from the scar). Our observations support the behavior of the avalanche beginning as a translational slide, and then as plug flow when confined within the Laja River valley. Clay abundance and high content of hydrothermally altered material may suggest active participation of water; flow velocities are estimated to?~100 m s^?1. We primarily identify the steep-sided flanks of the cone, and hydrothermal alteration promoted the edifice instability, while basement seismogenic structures may have ultimately triggered the landslide. Subsequent landslide-led events include the transformation of the volcanic activity with explosive eruptions producing a sequence of dilute pyroclastic density currents (PDCs) ending?~3.4 ky BP, and extensive lava effusion rapidly reconstructing the collapsed edifice. Moreover, the Antuco VDAD also blocked the natural output of the Laja Lake, increasing its level by?~200 m and then triggering cataclysmic outburst floods by dam rupture, preserved as high-energy alluvial beds with ages between 2.8 and 1.7 ky BP. The Antuco constitutes an excellent example of a critical chain of events initiated by a stratovolcano lateral collapse and warns for detailed hazard investigations to better comprehend its related impacts.

     

Alternant active and passive trapdoor problem: from experimental investigation to mathematical modeling

Acta Geotechnica - In the classical conception of the arching mechanism, the well-known trapdoor problem assumes distinctive modes (e.g., either active or passive mode) in the original geostatic...     

On the design and seismic response of RC frame buildings designed with Eurocode 8

Performance-Based Seismic Design is now widely recognized as the pre-eminent seismic design and assessment methodology for building structures. In recognition of this, seismic codes may require that buildings achieve multiple performance objectives such as withstanding moderate, yet frequently occurring earthquakes with minimal structural and non-structural damage, while withstanding severe, but rare earthquakes without collapse and loss of life. These objectives are presumed to be satisfied by some codes if the force-based design procedures are followed. This paper investigates the efficacy of the Eurocode 8 force-based design provisions with respect to RC frame building design and expected seismic performance. Four, eight, and 16-storey moment frame buildings were designed and analyzed using the code modal response spectrum analysis provisions. Non-linear time-history analyses were subsequently performed to determine the simulated seismic response of the structures and to validate the Eurocode 8 force-based designs. The results indicate the design of flexural members in medium-to-long period structures is not significantly influenced by the choice of effective member stiffness; however, calculated interstorey drift demands are significantly affected. This finding was primarily attributed to the code’s enforcement of a minimum spectral ordinate on the design spectrum. Furthermore, design storey forces and interstorey drift demand estimates (and therefore damage), obtained by application of the code force-based design procedure varied substantially from those found through non-linear time-history analysis. Overall, the results suggest that though the Eurocode 8 may yield life-safe designs, the seismic performance of frame buildings of the same type and ductility class can be highly non-uniform.     

First record of a clupeomorph fish in the Neuquén Group (Portezuelo Formation), Upper Cretaceous of Patagonia, Argentina

A new genus and species of clupeomorph fish, Leufuichthys minimus, is described from the fluvial deposits of the Portezuelo Formation, Upper Cretaceous (Turonian-Coniacian) of the Neuquén Group, Patagonia, Argentina. It is a small-sized fish with an estimated body length up to 46 mm. Among other characters, the new species shows the following: abdominal scutes; abdomen moderately convex; anal fin elongate-based; three uroneurals; two epurals; caudal fin bearing very elongate rays; and cycloid scales. Leufuichthys minimus gen. et sp. nov. shows a greater similarity with Kwangoclupea dartevellei, a clupeomorph described from a marine Cenomanian deposit of the Democratic Republic of Congo (Africa), mainly due to the presence of an elongate-based anal fin, bearing more than 20 fin-rays, differing from it by the presence of a not hypertrophied abdomen. As far as known, L. minimus gen. et sp. nov. is the first clupeomorph described in the Upper Cretaceous of Patagonia and represents one fortuitous preservation of an articulated fish in fluvial deposits.     

Evolution of a coastal alluvial deposit in response to the last Quaternary marine transgression, Bahía Blanca estuary, Argentina

The purpose of this research is to analyze the seismostratigraphic and paleoenvironmental features of an ancient fluvial deposit characterized by the presence of paleochannels and sedimentary structures in Bahía Blanca estuary, Argentina. To this end, high-resolution seismic methods were used. Paleochannels exhibiting v-shaped cuts were found at different topographic positions at the base of this deposit. It was observed that channel silting is indicative of the relative change of river base level and the consequent migration of fluvial tributaries. This alluvial deposit is composed of low compacted fine sand and its middle–upper facies is characterized by the presence of horizontal and discontinuous wavy reflectors. The upper boundary of this deposit is an erosive discontinuity resulting from Holocene sea-level rise during which the mouth of old fluvial courses underwent changes. The deposit was subsequently buried by sandy and clayey silt sediments. The paleodrainage at subbottom indicates that this deposit is associated with an ancient river mouth. Based on the seismostratigraphic and lithological characteristics and the paleochannel structures found in the study area, it can be concluded that the deposit analyzed is an alluvial sequence formed in the period from the Middle-Late Pleistocene to Holocene marine transgression.