Improved nutation series for the non–rigid earth with a precise adjustment of parameters with nonlinear dependence

In this paper, the previous nutation series corresponding to the rotation of a non‐rigid earth composed of a rigid mantle and a liquid core obtained by Getino and Ferrándiz in 1997 are notably improved by using a high performance data fitting method. This method can be applied to many other problems presenting a non‐linear dependence on the free parameters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Holocene recurrent explosive activity at Chimborazo volcano (Ecuador)

Ice-capped Chimborazo is one of the large composite Ecuadorian volcanoes whose recent eruptive activity is poorly known. This paper presents the characteristics and the ages of a newly discovered Holocene sequence of pyroclastic deposits on the east and north sides of the cone. Lying upon a moraine of the Late-Glacial period, the most complete section of ~ 4.5 m in thickness is located 5 km from the present summit crater. It consists of seven massive or diffusely stratified ash flow layers and four fallout layers interbedded with seven paleosoils.     

Pre-eruptive physical conditions of El Reventador volcano (Ecuador) inferred from the petrology of the 2002 and 2004–05 eruptions

A petrological study of the eruptive products of El Reventador allowed us to infer the magmatic processes related to the 2002 and 2004–05 eruptions of this andesitic stratovolcano. On November 3, 2002, El Reventador experienced a highly explosive event, which was followed by emplacement of two lava flows in November–December 2002. Silica contents range from 62 to 58 wt.% SiO₂ for the November 3 pyroclastic deposits to 58–56 and 54–53 wt.% SiO₂ for the successive lava flows. In November 2004 eruptive activity resumed supplying four new lava flows (56–54 wt.% SiO₂) between November 2004 and August 2005.     

Late Holocene phases of dome growth and Plinian activity at Guagua Pichincha volcano (Ecuador)

Since the eruption which affected Quito in AD 1660, Guagua Pichincha has been considered a hazardous volcano. Based on field studies and twenty ¹⁴C dates, this paper discusses the eruptive activity of this volcano, especially that of the last 2000 years. Three major Plinian eruptions with substantial pumice discharge occurred in the 1st century, the 10th century, and in AD 1660. The ages of organic paleosols and charcoal from block-and-ash flow and fallout deposits indicate that these eruptions occurred near the end of 100 to 200 year-long cycles of discontinuous activity which was comprised of dome growth episodes and minor pumice fallouts. The first cycle took place from ~ AD 1 to 140. The second one developed during the 9th and 10th centuries, lasted 150–180 yr, and included the largest Plinian event, with a VEI of 5. The third, historic cycle, about 200 yr in duration, includes pyroclastic episodes around AD 1450 and AD 1500, explosive activity between AD 1566 and AD 1582, possible precursors of the 1660 eruption in the early decades of the 17th century, and finally the 1660 eruption (VEI 4). A fourth event probably occurred around AD 500, but its authenticity requires confirmation. The Plinian events occurred at the end of these cycles which were separated by repose periods of at least 300 yr. Older volcanic activity of similar type occurred between ~ 4000 and ~ 3000 yr BP.     

The Coherent Pixels Technique (CPT): An Advanced DInSAR Technique for Nonlinear Deformation Monitoring

This paper shows the potential applicability of orbital Synthetic Aperture Radar (SAR) Differential Interferometry (DInSAR) with multiple images for terrain deformation episodes monitoring. This paper is focused on the Coherent Pixels Technique (CPT) developed at the Remote Sensing Laboratory (RSLab) of the Universitat Politecnica de Catalunya (UPC). CPT is able to extract from a stack of differential interferograms the deformation evolution over vast areas during wide spans of time. The former is achieved thanks to the coverage provided by current SAR satellites, like ESA’s ERS or ENVISAT, while the latter due to the large archive of images acquired since 1992. An interferogram is formed by the complex product of two SAR images (one complex conjugate) and its phase contains information relative to topography, terrain deformation and atmospheric conditions among others. The goal of differential interferometric processing is to retrieve and separate the different contributions. The processing scheme is composed of three main steps: firstly, the generation of the best interferogram set among all the available images of the zone under study; secondly, the selection of the pixels with reliable phase within the employed interferograms and, thirdly, their phase analysis to calculate, as the main result, their deformation time series within the observation period. In this paper, the Coherent Pixels Technique (CPT) is presented in detail as well as the result of its application in different scenarios. Results reveal its practical utility for detecting and reproducing deformation episodes, providing a valuable tool to the scientific community for the understanding of considerable geological process and to monitor the impact of underground human activity.     

A spatio-temporal Poisson hurdle point process to model wildfires

Wildfires have been studied in many ways, for instance as a spatial point pattern or through modeling the size of fires or the relative risk of big fires. Lately a large variety of complex statistical models can be fitted routinely to complex data sets, in particular wildfires, as a result of widely accessible high-level statistical software, such as R. The objective in this paper is to model the occurrence of big wildfires (greater than a given extension of hectares) using an adapted two-part econometric model, specifically a hurdle model. The methodology used in this paper is useful to determine those factors that help any fire to become a big wildfire. Our proposal and methodology can be routinely used to contribute to the management of big wildfires.     

Characterization of wood-laden flows in rivers

Inorganic sediment is not the only solid-fraction component of river flows; flows may also carry significant amounts of large organic material (i.e. large wood), but the characteristics of these wood-laden flows (WLFs) are not well understood yet. With the aim to shed light on these relatively unexamined phenomena, we collected home videos showing natural flows with wood as the main solid component. Analyses of these videos as well as the watersheds and streams where the videos were recorded allowed us to define for the first time WLFs, describe the main characteristics of these flows and broaden the definition of wood transport regimes (adding a new regime called here hypercongested wood transport). According to our results, WLFs may occur repeatedly, in a large range of catchment sizes, generally in steep, highly confined single thread channels in mountain areas. WLFs are typically highly unsteady and the log motion is non-uniform, as described for other inorganic sediment-laden flows (e.g. debris flows). The conceptual integration of wood into our understanding of flow phenomena is illustrated by a novel classification defining the transition from clear water to hypercongested, wood and sediment-laden flows, according to the composition of the mixture (sediment, wood, and water). We define the relevant metrics for the quantification and modelling of WLFs, including an exhaustive discussion of different modelling approaches (i.e. Voellmy, Bingham and Manning) and provide a first attempt to simulate WLFs. We draw attention to WLF phenomena to encourage further field, theoretical, and experimental investigations that may contribute to a better understanding of flows in river basins, leading to more accurate predictions, and better hazard mitigation and management strategies. © 2019 John Wiley & Sons, Ltd.     

Out-of-plane shaking table tests of full-scale historic adobe corner walls retrofitted with timber elements

Historic adobe structures pose a high seismic risk mainly because of the poor out-of-plane bending response of their walls that may produce fatalities and significant economic, cultural, and heritage losses. In this paper, we propose a retrofitting technique that increases the wall strength for both in-plane and out-of-plane directions. This technique consists of vertical and horizontal timber elements symmetrically installed on each face of the wall to form a confining wood frame, supplemented with vertical tensors that pre-compress the wall. This study evaluates the performance of this retrofitting technique with a two-set experimental program on full-scale historic adobe walls. On the first set, four specimens were subjected to a static overturning test with boundary conditions representing the confinement effect at both ends by orthogonal walls. On the second set, three full-scale specimens, one unretrofitted and two retrofitted, were subjected to four ground motion records on a shaking table to assess the out-of-plane dynamic behavior of typical corner walls. The unretrofitted specimen collapsed during the second motion (peak ground acceleration [PGA] = 0.39 g), while both retrofitted walls survived all four motions (maximum PGA of 0.75 g) proving the high effectiveness of the proposed retrofitting. The addition of base anchors as a variation of the retrofitting technique significantly reduced the rocking effects and the residual drifts of the system, thus improving its overall seismic performance. Further research is needed to develop guidelines for seismic retrofit of heritage buildings including multistory full-scale tests of specimens with various types of openings and retrofitting strategies that minimize their architectural impact.     

Generalized algorithms for particle motion and collision with streambeds

Recent theoretical and numerical models for the motion of saltating particles close to stream beds are constituted of three sub-models: a) a set of equations describing the particle “free flight”, b) a sub-model to calculate the post-collision particle velocity, and c) a mathematical representation of the bed roughness. In this paper, a comprehensive three-dimensional (3-D), theoretical/numerical model for bedload motion at large Reynolds numbers is presented. By using geometric considerations and stochastic parameters to characterize collisions with the wall, five new sub-models for representation of bed roughness are, for the first time to the best of our knowledge, proposed and implemented. The emphasis of this paper is on the particle model, for which Basset, Magnus, drag, submerged weight, virtual mass, and lift forces are included. For the range of particle sizes (sands) analyzed herein, it is found that the stream-wise contribution of the Basset force, compared to other forces, may be as large as 60%. Whereas in the wall-normal direction, the Basset force is equally important as the drag force, and it is exceeded only by the submerged weight. It is also found that the best agreement between numerical and experimental results in terms of jump length, jump height, and stream-wise particle velocity is achieved for restitution and friction coefficients of 0.65 and 0.1, respectively. Important conclusions are obtained regarding the lack of realistic prediction with available “roughness” models with small ranges of angles.