Hasil untuk "Dynamic and structural geology"

Hui Jiang, Yao-Yun Yuan, Jin-Ting Wang et al.

Beatriz Silva Fernandes, Stefania Cristino de Oliveira, Fabiano N. Pupim

Land use changes and dam construction have impacted sediment yield in river catchments worldwide. This is especially true in central-west Brazil, where most of the main watersheds have been deforested and rivers, such as the Cuiabá, have been dammed in the last 50 years. Here, we investigated the geomorphological and sedimentary responses of the Cuiabá River to land use changes and dams since 1985, using a time-series of Landsat images to quantify fluvial bars, channel width, channel migration rate and suspended sediment concentration (SSC). Our results showed an increase in the area occupied by fluvial bars and in SSC between 1985 and 2000, driven by natural vegetation conversion to agriculture. However, construction of the Manso Dam in 2000 led to a decrease in bar area, migration rates and SCC downstream. The SSC time-series also showed that sediment production remains high up to the present day in the monitoring section upstream of the Manso Dam, triggered by new waves of deforestation since the early 2000s. We conclude that land cover change led to increased sediment supply to the Cuiabá River, especially before the 2000s. However, this effect was surpassed by dam constructions in the watershed, which drove a significant decrease in sediments exported downstream.

M. Li, M. Li, X. Li et al.

<p>Soybean is the most important oilseed and feed crop globally. As one of the major soybean producers in the world, soybean yield variability in the United States has garnered widespread attention. We analyze the effect of the Indian Ocean sea surface temperature (SST) on soybean yield variability. Our findings indicate that variations in Indian Ocean SST during the November–December–January (hereinafter referred to as ND(-1)J) period, approximately 9 months prior to harvest, account for 16 % of the anomaly in US soybean yields. Furthermore, for each standard deviation change in the Indian Ocean Basin (IOB) index, there is an estimated 4.0 % change in total soybean production in the United States. The root zone soil moisture and maximum temperature during the reproductive growth stage in summer are the key factors influencing the United States soybean yields. The warming of the Indian Ocean could cause hot and dry conditions during July–August–September (JAS) by influencing ND(-1)J soil moisture and the eastern Pacific SST, leading to substantial soybean failures in the United States. Our findings emphasize the importance of the Indian Ocean SST on soybean production in the United States and reveal the pathways of this impact, which can help predict the United States soybean failures and improve food security worldwide.</p>

Hugo Boulze, Jean-Didier Garaud, Emilie Klein et al.

Megaearthquakes (Mw > 8) cause continental-scale, long-lasting surface deformation, mainly due to viscoelastic relaxation of the asthenosphere. To investigate the links between this deformation and the slip history along subduction interfaces—including earthquakes, postseismic slip, and interseismic coupling—large 3D spherical finite-element meshes are required.   This technical report introduces the various steps to build Chile_Mesh_v1.0, a customizable mesh for the Chilean subduction zone, designed as a robust platform for testing various viscoelastic rheologies. It spans ~8500 km in longitude, ~7300 km in latitude, encompassing the entire South American plate, and from the surface to 2900 km depth. Special care was taken to reproduce the complex slab geometry, especially in flat-slab regions such as the Pampean and Peruvian segments, following the Slab2 model.   We show that accurately modeling both coseismic and postseismic deformation over large scales requires realistic meshed domains, extending down to the Core-Mantle boundary and thousands of kilometers from the trench. In some cases, depth-reduced meshes can be used to model viscoelastic postseismic deformation, but they fail to simultaneously capture coseismic deformation accurately. We hope this open-access mesh proves valuable for researchers studying subduction dynamics in Chile and supports the development of similar models for other regions.

Hailiang Liu, Chan-Ching Wang, Di Wu et al.

Baohong Lv, Changming Wang, Zefang Zhang et al.

S. Abushova, Narmin Salmanli

In the present article, the impact of relief’s static and dynamic factors on the eco-logical conditions was analyzed based on the concept of the environment-forming function of relief. The research area is located in Azerbaijan, between the Khram and Zayam rivers on the north-eastern slope of the Lesser Caucasus, and its total area is 2358 km². Relief is an essential factor shaping land use; in this regard, the ecogeomorphological assessment of an area is very relevant in terms of land use. First, structural-lithological, morphological, and morphometric (horizontal and vertical dissection of relief, a slope of the surface, exposition of slopes) features of relief and their impact on the ecological conditions are studied. Then, endodynamic and exodynamic processes, the latest and current movements, mobility of magmatic bodies, fluvial, gravitational, karst processes of morphogenesis and their environment-forming impact on the ecosystem are explained. Finally, the results of the analysis of ecogeomorphological tension were created in the program Arcmap 10.4, and zonation of the studied territory was carried out. It should also be noted that within a region with the same ecogeomorphological tension there is a limited range of areas with different degrees of tension. In the territories of low tension, weakness in exogenous processes and morphometric parameters stands as a sign of relief stability in the area. Based on our analyses, the studied region was subdivided in the areas with weak (36 %), moderate (35%), relatively high (24 %), and high (5%) tensions. The abovementioned figures suggest that a large part of the study area is suitable for infrastructure development and agricultural organization. A very small part consists of bare rocks and does not provide conditions for any agricultural activities. The high mountainous zones are only suitable for sports tourism. Here the areas where the population is more concentrated and land use is most suitable are the Ganja-Gazakh and Hunan plains, as well as the Bashkand-Dastafur depression. In contrast, the most tense areas are the highlands of the Chinggili ridge and the north-eastern slopes of the Shahdag and Murguz ridges.

G. Davis

Kunsheng Gu, Jian Zhou, Mingzhu Guo

A. Narayanan, A. Narayanan, S. Cohen et al.

<p>The Amazon experiences thousands of square kilometers of deforestation annually with recent rates increasing to levels unseen since the late 2000s. These increased rates of deforestation within the basin have led to changes in sediment concentration within its river systems, with potential impacts on ecological functioning, freshwater availability, and fluvial and coastal geomorphic processes. The relationship between deforestation and fluvial sediment dynamics in the Amazon has not been extensively studied using a basin-wide, comparative approach primarily due to lack of data. In this study, we utilize a novel remote-sensing-derived sediment concentration dataset to analyze the impact of deforestation from 2001 to 2020 on suspended sediment in large rivers (<span class="inline-formula">&gt;50</span> m wide) across the Amazon River basin. These impacts are studied using a lag-based approach to quantify the spatiotemporal relationships between observed suspended sediment and changes in land cover over time. The results show that large-scale deforestation of the Amazon during the 2001–2020 period are associated with significant changes in sediment concentration in the eastern portion of the basin. In the heavily deforested eastern regions, the hydrogeomorphic response to deforestation occurs relatively rapidly (within a year), whereas the less disturbed western areas exhibit delays of 1 to 2 years before responses are observable. Moreover, we observe that deforestation must be substantial enough to overcome the collective influences of human activities and natural sediment variations to result in a discernible impact on sediment concentration in large rivers. In 69 % of Amazonian major tributary basins with an immediate response, more than 5 % of the basin was deforested during the 2001–2020 period, while in 85 % of basins with lagged responses, less than 5 % of the land was cleared. These findings suggest severe implications for future sediment dynamics across the Amazon if deforestation is to further expand into the basin.</p>

M. Vrac, D. Allard, G. Mariéthoz et al.

<p>For investigating, assessing, and anticipating climate change, tens of global climate models (GCMs) have been designed, each modelling the Earth system slightly differently. To extract a robust signal from the diverse simulations and outputs, models are typically gathered into multi-model ensembles (MMEs). Those are then summarized in various ways, including (possibly weighted) multi-model means, medians, or quantiles. In this work, we introduce a new probability aggregation method termed “alpha pooling” which builds an aggregated cumulative distribution function (CDF) designed to be closer to a reference CDF over the calibration (historical) period. The aggregated CDFs can then be used to perform bias adjustment of the raw climate simulations, hence performing a “multi-model bias correction”. In practice, each CDF is first transformed according to a non-linear transformation that depends on a parameter <span class="inline-formula"><i>α</i></span>. Then, a weight is assigned to each transformed CDF. This weight is an increasing function of the CDF closeness to the reference transformed CDF. Key to the <span class="inline-formula"><i>α</i></span> pooling is a parameter <span class="inline-formula"><i>α</i></span> that describes the type of transformation and hence the type of aggregation, generalizing both linear and log-linear pooling methods. We first establish that <span class="inline-formula"><i>α</i></span> pooling is a proper aggregation method by verifying some optimal properties. Then, focusing on climate model simulations of temperature and precipitation over western Europe, several experiments are run in order to assess the performance of <span class="inline-formula"><i>α</i></span> pooling against methods currently available, including multi-model means and weighted variants. A reanalysis-based evaluation as well as a perfect model experiment and a sensitivity analysis to the set of climate models are run. Our findings demonstrate the superiority of the proposed pooling method, indicating that <span class="inline-formula"><i>α</i></span> pooling presents a potent way to combine GCM CDFs. The results of this study also show that our unique concept of CDF pooling strategy for multi-model bias correction is a credible alternative to usual GCM-by-GCM bias correction methods by allowing handling and considering several climate models at once.</p>

David Naranjo, Laura Parisi, Sigurjón Jónsson et al.

Ocean-bottom seismometers (OBSs) are equipped with seismic sensors that record acoustic and seismic events at the seafloor, which makes them suitable for investigating tectonic structures capable of generating earthquakes offshore. One critical parameter to obtain accurate earthquake locations is the absolute time of the incoming seismic signals recorded by the OBSs. It is, however, not possible to synchronize the internal clocks of the OBSs with a known reference time, given that GNSS signals are unable to reach the instrument at the sea bottom. To address this issue, here we introduce a new method to synchronize the clocks of large-scale OBS deployments. Our approach relies on the theoretical time-symmetry of time-lapse (averaged) crosscorrelations of ambient seismic noise. Deviations from symmetry are attributed to clock errors. This implies that the recovered clock errors will be obscured by lapse crosscorrelations' deviations from symmetry that are not due to clock errors. Non-uniform surface wave illumination patterns are arguably the most notable source which breaks the time symmetry. Using field data, we demonstrate that the adverse effects of non-uniform illumination patterns on the recovered clock errors can be mitigated by means of a weighted least-squares inversion that is based on station-station distances. In addition, our methodology permits the recovery of timing errors at the time of deployment of the OBSs. This error can be attributed to either: i) a wrong initial time synchronization of the OBS or ii) a timing error induced by changing temperature and pressure conditions while the OBS is sunk to the ocean floor. The methodology is implemented in an open-source Python package named OCloC, and we applied it to the OBS recordings acquired in the context of the IMAGE project in and around Reykjanes, Iceland. As expected, most OBSs suffered from clock drift. Surprisingly, we found incurred timing errors at the time of deployment for most of the OBSs.

Великанов Петр Геннадьевич, Артюхин Юрий Павлович

Определение собственных и вынужденных колебаний рамных конструкций, моделируемых стержнями с распределенными массами (бесконечное число степеней свободы), довольно затруднительно. Поэтому в статье модель рамы наделяют конечным числом степеней свободы: массу помещают в некоторое число узлов, которые упруго взаимодействуют со стержнями, не имеющими массы. Стержни работают только на изгиб. Продольные перемещения не учитываются, так как частота продольных колебаний на два порядка выше частоты изгибных колебаний. Такая модель позволяет составить выражения кинетической и потенциальной энергии и затем с помощью уравнений Лагранжа 2-го рода получить систему дифференциальных уравнений колебаний многоэтажных зданий. В статье с использованием функций Грина, матриц жесткости, масс, податливости и др. была решена задача о свободных колебаниях Г-образной рамы. Полученные приближенные результаты при сравнении с малоизвестными точными результатами показали хорошую сходимость, особенно при увеличении числа степеней свободы (количества сосредоточенных масс, моделирующих распределенную массу стержней Г-образной рамы).

A. A. Ermilov, G. Benkő, S. Baranya

<p>The sediment of alluvial riverbeds plays a significant role in river systems both in engineering and natural processes. However, the sediment composition can show high spatial and temporal heterogeneity, even on river-reach scale, making it difficult to representatively sample and assess. Conventional sampling methods are inadequate and time-consuming for effectively capturing the variability of bed surface texture in these situations. In this study, we overcome this issue by adopting an image-based deep-learning (DL) algorithm. The algorithm was trained to recognise the main sediment classes in videos that were taken along cross sections underwater in the Danube. A total of 27 riverbed samples were collected and analysed for validation. The introduced DL-based method is fast, i.e. the videos of 300–400 m long sections can be analysed within minutes with continuous spatial sampling distribution (i.e. the whole riverbed along the path is mapped with images in ca. 0.3–1 m<span class="inline-formula">²</span> overlapping windows). The quality of the trained algorithm was evaluated (i) mathematically by dividing the annotated images into test and validation sets and also via (ii) intercomparison with other direct (sieving of physical samples) and indirect sampling methods (wavelet-based image processing of the riverbed images), focusing on the percentages of the detected sediment fractions. For the final evaluation, the sieving analysis of the collected physical samples were considered the ground truth. After correcting for samples affected by bed armouring, comparison of the DL approach with 14 physical samples yielded a mean classification error of 4.5 %. In addition, based upon the visual evaluation of the footage, the spatial trend in the fraction changes was also well captured along the cross sections. Suggestions for performing proper field measurements are also given; furthermore, possibilities for combining the algorithm with other techniques are highlighted, briefly showcasing the multi-purpose nature of underwater videos for hydromorphological assessment.</p>

Mark Ireland, Guillermo Algarabel, Michael Steventon et al.

Geophysical research frequently makes use of agreed-upon methodologies, formally published software, and bespoke code to process and analyse data. The reliability and repeatability of these methods is vital in maintaining the integrity of research findings and thereby avoiding the dissemination of unreliable results. In recent years there has been increased attention on aspects of reproducibility, which includes data availability, across scientific disciplines. This review considers aspects of reproducibility of geophysical studies relating to their publication in peer reviewed journals. For 100 geophysics journals it considers the extent to which reproducibility in geophysics is the focus of published literature. For 20 geophysical journals it considers a) journal policies on the requirements for providing code, software, and data for submission; and b) the availability of data and software associated for 200 published journal articles. The findings show that: 1) between 1991 and 2021 there were 72 articles with reproducibility in the title and 417 with reliability, with an overall increase in the number of articles with reproducibility or reliability as the subject over the same period; 2) while 60% of journals have a definition of research data, only 20% of journals have a requirement for a data availability statement; and 3) despite ~86% of sampled journal articles including a data availability statement, only 54% of articles have the original data accessible via data repositories or web servers, and only 49% of articles name software used. It is suggested that despite journals and authors working towards improving the availability of data and software, frequently they are not identified, or easily accessible, therefore limiting the possibility of reproducing studies.

D. Rickenmann, L. Ammann, T. Nicollier et al.

<p>The Swiss plate geophone (SPG) system has been installed and tested in more than 20 steep gravel-bed streams and rivers, and related studies generally resulted in rather robust calibration relations between signal impulse counts and transported bedload mass. Here, we compare this system with three alternative surrogate measuring systems. A variant of the SPG system uses the same frame (housing) set-up but with an accelerometer instead of a geophone sensor to measure the vibrations of the plate (GP-Acc, for geophone plate accelerometer). The miniplate accelerometer (MPA) system has a smaller dimension of the impact plate and is embedded in more elastomer material than the SPG system. The Japanese pipe microphone (JPM) is a 1 m long version of the system that has been installed in many streams in Japan. To compare the performance of the four systems, we used calibration measurements with direct bedload samples from three field sites and an outdoor flume facility with controlled sediment feed. At our field sites, the systems with an accelerometer and a microphone showed partly large temporal variations in the background noise level, which may have impaired the calibration measurements obtained during certain time periods. Excluding these periods, the SPG, GP-Acc, and JPM all resulted in robust calibration relations, whereas the calibration of the MPA system showed a poorer performance at all sites.</p>

T. Kenkmann, M. Poelchau, G. Wulf

T. Zlobina, V. Petrov, V. Prokofiev et al.

M. Wegmann, M. Rohrer, M. Rohrer et al.

<p>In recent years, many components of the connection between Eurasian autumn snow cover and wintertime North Atlantic Oscillation (NAO) have been investigated, suggesting that November snow cover distribution has strong prediction power for the upcoming Northern Hemisphere winter climate. However, the non-stationarity of this relationship could impact its use for prediction routines. Here we use snow products from long-term reanalyses to investigate interannual and interdecadal links between autumnal snow cover and atmospheric conditions in winter. We find evidence for a negative NAO-like signal after November with a strong west-to-east snow cover gradient, which is valid throughout the last 150 years. This correlation is consistently linked to a weak stratospheric polar vortex state. Nevertheless, decadal evolution of this link shows episodes of decreased correlation strength, which co-occur with episodes of low variability in the November snow index. By contrast, periods with high prediction skill for winter NAO are found in periods of high November snow variability, which co-occur with the Arctic warming periods of the 20th century, namely the early 20th-century Arctic warming between 1920 and 1940 and the ongoing anthropogenic global warming at the end of the 20th century. A strong snow dipole itself is consistently associated with reduced Barents–Kara sea ice concentration, increased Ural blocking frequency and negative temperature anomalies in eastern Eurasia.</p>

E. Lemaire, Anne-Sophie Mreyen, H. Havenith