Dynamic Earth Research Articles

The Effect of Elementary Education on the Relationship of Social Science to the Earth's Governance System

The sustainability of this research from Biermann has a focus on collaborating on the earth system governance network based on five research challenges namely architecture, agency, adaptability, allocation, and accountability. Research in order to link the relationship of social science with the earth's governance system. It turns out that the social system is very influential in the earth's governance system, so the need to instill the value of the value of love of nature since elementary education so that the impact of the social system on the earth's governance system in the future can be minimized. The results of this study indicate that social systems consisting of people, governments, and non-government actors must work together to deal with the impact of a dynamic earth governance system. For this reason, elementary education is needed to reduce the negative impact of changes in the earth's governance system through the cultivation of character education that loves the environment while having a sense of responsibility.

Mineralogy of microbially induced calcium carbonate precipitates formed using single cell drop-based microfluidics

Microbe-mineral interactions are ubiquitous and can facilitate major biogeochemical reactions that drive dynamic Earth processes such as rock formation. One example is microbially induced calcium carbonate precipitation (MICP) in which microbial activity leads to the formation of calcium carbonate precipitates. A majority of MICP studies have been conducted at the mesoscale but fundamental questions persist regarding the mechanisms of cell encapsulation and mineral polymorphism. Here, we are the first to investigate and characterize precipitates on the microscale formed by MICP starting from single ureolytic E. coli MJK2 cells in 25 µm diameter drops. Mineral precipitation was observed over time and cells surrounded by calcium carbonate precipitates were observed under hydrated conditions. Using Raman microspectroscopy, amorphous calcium carbonate (ACC) was observed first in the drops, followed by vaterite formation. ACC and vaterite remained stable for up to 4 days, possibly due to the presence of organics. The vaterite precipitates exhibited a dense interior structure with a grainy exterior when examined using electron microscopy. Autofluorescence of these precipitates was observed possibly indicating the development of a calcite phase. The developed approach provides an avenue for future investigations surrounding fundamental processes such as precipitate nucleation on bacteria, microbe-mineral interactions, and polymorph transitions.

Large-scale shaking table test on seismic behaviour of anti-slide pile-reinforced bridge foundation and gravel landslide: a case study

This study aimed to illustrate the seismic response and instability process of a double-row anti-slide pile-reinforced bridge foundation and gravel landslide. Selecting the gravel slope of Jiuzhai Valley along the under-construction Chengdu-Lanzhou high-speed railway as the site prototype, large-scale shaking table tests were first conducted at a similitude ratio of 1:70, with sine waves and El Centro waves as the seismic wave inputs. The amplitudes of the input seismic waves were increased, while the acceleration, dynamic earth pressure, and strain distribution were monitored in the gravel landslide. The dynamic response patterns of anti-slide pile-reinforced bridge foundations in gravel landslides were illustrated. The front-row and back-row anti-slide piles should be a reasonable distance from the bridge foundation. The response acceleration manifested an elevation amplification effect with an increasing elevation in the slope behind the anti-slide piles. Back-row anti-slide piles reinforcing the bridge foundation can reduce the effect of landslide thrust on the bridge foundation and maintain a uniform distribution of earth pressure behind the bridge foundation, mitigating seismic effects. The dynamic earth pressure peaked at the top of the bridge foundation and then decreased along the depth. The back-row anti-slide piles displayed greater resonance coupling and unloading effects before and after reaching the load-carrying limit, respectively. In seismic strengthening design involving bridge foundations and gravel landslides, when the earthquake-induced resonance coupling effect on inclined, loosely packed land masses is fully considered, pre-reinforcement measures (e.g., high-pressure grouting and anchor spraying) should be carried out on the gravel slopes.

Shaking table investigations on seismic performance of prefabricated corrugated steel utility tunnels

A series of shaking table model tests were performed to investigate dynamic responses and damage mechanisms of prefabricated corrugated steel utility tunnels holding various brackets and pipelines. Details of the shaking table experimental setup for this kind of new utility tunnel are presented in this paper for the first time. Multiple seismic responses are measured, including the displacement of the soil surface, acceleration and strain of the utility tunnel, pipelines and brackets, as well as the acceleration and dynamic earth pressure of the test soil. The results demonstrate that the model box designed by our lab did not impose an obvious boundary effect. Displacement of the overlying soil above two sides of the utility tunnel was larger than that of the center of the model in the field nearby. The acceleration response of the structure was perfectly consistent with the surrounding soil. Dynamic earth pressures acting against the tunnel sidewall were significantly affected by the tunnel’s mass distribution under strong excitations. Response acceleration varied with different kinds of pipelines and brackets. The peak strain obtained from the suspending bracket was larger than that of the standing bracket. Different types of brackets were suitable for different applications. Both of the utility tunnel and brackets were not yielded under strong ground motions. The results provide valuable insight into the seismic performance of the shallow-buried underground steel structure and the safe design of the prefabricated corrugated steel utility tunnel.

Terrain, politics, history

This article is based on the 2019 Dialogues in Human Geography plenary lecture at the Royal Geographical Society. It has four parts. The first discusses my work on territory in relation to recent work by geographers and others on the vertical, the volumetric, the voluminous, and the milieu as ways of thinking space in three-dimensions, of a fluid and dynamic earth. Second, it proposes using the concept of terrain to analyse the political materiality of territory. Third, it adds some cautions to this, through thinking about the history of the concept of terrain in geographical thought, which has tended to associate it with either physical or military geography. Finally, it suggests that this work is a way geographers might begin to respond to the challenge recently made by Bruno Latour, where he suggests that ‘belonging to a territory is the phenomenon most in need of rethinking and careful redescription; learning new ways to inhabit the Earth is our biggest challenge’. Responding to Latour continues this thinking about the relations between territory, Earth, land, and ground, and their limits.

Investigations of seismic response to an irregular-section subway station structure located in a soft clay site

In this study, shaking table tests were performed to investigate the dynamic interaction of a silty-clay soil with an irregular-section subway station. During the tests, a shape acceleration array (SAA) was used to measure the lateral deformation of the model soil, and a non-contact dynamic displacement testing method was applied to visualize and digitalize the seismic damage process of the station structure. Typical test results, including the dynamic earth pressure, seismic settlement, deformation, and acceleration of different levels of the structure, were interpreted. The results indicated that the movement of the subway station was more controlled by the surrounding silty-clay soil in terms of phase and amplitude. SAA can effectively measure the soil deformation, and the relationship between the relative lateral displacement and soil depth can be well fitted in a cosine function, especially when subjected to strong earthquakes. Seismic settlement is significantly linked to Arias intensity, and the subway station experienced significant uneven settlement, resulting in soil-structure separation in the vertical direction. The multi-story irregular-section subway station deforms in a shear mode. The maximum inter-story drift ratio was approximately 1/171. The components in the lower layers of the shallow-buried subway station structure, particularly in the central columns, underwent cumulative damage. Hence, more robust forms of structural members and the ductility of central columns should be carefully considered in the seismic design of subway station structures.

Study on seismic behaviors of a double box utility tunnel with joint connections using shaking table model tests

Shaking table model tests were carried out to study the seismic behaviors of double box utility tunnel with joint connections and the surrounding soil. The seismic wave obtained from 1952 Taft earthquake was employed as the input in this study, and its PGA has been adjusted to 0.2 g, 0.4 g, 0.8 g, and 1.2 g, respectively. In addition, a series of sine waves with PGA of 0.2 g and frequencies of 5 Hz, 10 Hz, 15 Hz, 20 Hz, 25 Hz, and 30 Hz were applied to study the effect of frequency characteristics on seismic behavior of the utility tunnel and the surrounding soil. The testing results show that the laminar soil container does not impose significant boundary effect, and the dynamic earth pressure response is significantly influenced due to existence of the joint connection. Besides, the effect of soil-structure interaction on seismic behaviors is becoming even more obvious as the input PGA increases. The acceleration response is also significantly influenced by the dynamic property of the soil. Greater bending moment occurs at the corners of the structure, and its increasing ratio will decrease with an increasing input PGA magnitude. Lastly, the effect of frequency is significant. Therefore, it is noteworthy that the possible effect of natural frequency is considered when the utility tunnel is under construction.

Experimental study on seismic response of soilbags-built retaining wall

The seismic performance of soilbags-built retaining wall model was studied experimentally. A series of small-scale shaking table tests with the input of different amplitude sinusoidal waves and a large-scale shaking table test in a designed laminar shear box with the input of the Wenchuan earthquake wave were carried out on soilbags' retaining wall models. For comparison, the small-scale shaking table tests were also conducted on horizontally reinforced retaining wall models. The horizontal acceleration responses, the Fourier spectra, the dynamic earth pressure and the lateral displacements of soilbags' retaining wall models were investigated in shaking table tests. The results show that the seismic response of the soilbags' retaining wall is equivalent to or even slightly better than that of the horizontally reinforced retaining wall. The fundamental frequency and the Fourier spectral characteristics of the soilbags’ retaining wall are similar to those of backfill sands. The dynamic earth pressure of the wall model fluctuates almost synchronously with the input Wenchuan wave and no residual earth pressure is induced by the seismic loading. The permanent lateral displacements are small when subjected to multiple shakings, providing a proof that the retaining wall of soilbags has a good seismic performance.

Dynamic response characteristics and failure mode of slopes on the loess tableland using a shaking-table model test

Loess tablelands are widely distributed in the center of the Loess Plateau. The percentage of the Loess Plateau area that experiences seismic intensities greater than or equal to level VII is 54.21%. Because of the gravity of the loess slope and a large number of vertical pores, the fissures are mostly developed in the Loess Plateau. The fissures can easily cause slope instability subjected to earthquakes. Considering the structural characteristics of loess tableland slopes and earthquakes, a shaking-table test on slope models with and without fissures is conducted to study the dynamic response characteristics and the law of deformation and instability of the slopes under seismic action. The results indicate that the amplification factors of peak ground acceleration (PGA) in the vicinity of the fissures in the loess slope are significantly higher than those in the non-fissure slope, which reaches a maximum value of 3.6 at the shoulder of slope (measuring point A15). Dynamic earth pressures have stress concentration in the middle and upper part (0.7 times slope height) near the fissure, which affects the variation law of slope earth pressure. The failure mode of the fissure slope is as follows: fissure development, fissure expansion, soil collapse at the slope shoulder, shear failure at high-position on the slope, shear failure at low-position on the slope, and formation of new fissures at the edge of the tableland.

EXPERIMENTAL STUDY OF SEISMIC RESPONSE OF THE SQUARE TUNNEL IN GRANULAR SOIL

In this study a series of shaking table tests were carried out to investigate the effect of tunnel model depth and direction of ground acceleration on the horizontal acceleration of tunnel model and soil beside it, ground surface settlement, and the dynamic earth pressure on the tunnel wall. Square tunnel model embedded in both dry and saturated soil (Karbala Sand). It subjected to three input sinusoidal motions 0.05g, 0.1g, and 0.2g. Two relative densities used, 30% for the upper layer and 70% for the lower layer. The results obtained indicate that the direction of seismic loading has significant effect on the horizontal acceleration of tunnel model. The increase of tunnel model depth lead to decrease the horizontal acceleration of tunnel model. While, the settlement of soil surface increases with an increase of tunnel model depth and ground acceleration especially at 0.2g earthquake loading. The change of direction of seismic loading leads to a small change in the settlement for dry soil. The results appear that dynamic earth pressure (DEP) was positive in dry soil and negative in saturated soil in all test. In saturated soil, the effect of direction of ground acceleration and depth of tunnel model on DEP in 0.2g is quite little.

Seismic behavior of a single-form lattice anchoring structure and a combined retaining structure supporting soil slope: a comparison

The lattice anchoring structure is a widely used single-form retaining structure to enhance the stability of soil slope. Meanwhile, the lattice anchoring beam is commonly combined with a gravity wall, namely a combined retaining structure, to support the high slope in engineering practice. In this study, the numerical models for both a single-form lattice anchoring structure and a combined retaining structure were established using FLAC3D code. The Wenchuan ground motions with different amplitudes were applied to investigate and compare the seismic response of the single-form lattice anchoring structure and the combined retaining structure regarding the earth pressure response, the deformation response, the mechanical characteristic of anchor and the element state of structure during earthquake. The numerical results were verified by shaking table test in terms of the dynamic earth pressure response and the axial stress of anchor. Although an intense earth pressure response was observed behind the combined retaining wall, the combined retaining structure was recommended to support the high slope in high seismic intensity region instead of the single-form lattice anchoring structure in view of the deformation of structure, the axial stress of anchor and the failure state of element.

Seismic performances of three- and four-sided box culverts: A comparative study

Studying the critical response characteristics of box culverts with diverse geometrical configurations under seismic excitations is a necessary step to develop a reasonable design method. In this work, a numerical parametric study is conducted on various soil-culvert systems, aiming to highlight the critical difference in the seismic performances between three- and four-sided culverts. Two-dimensional numerical models consider a variety of burial depths, flexibility ratios and foundation widths, assuming a visco-elastic soil condition, which permits to compare with the analytical solutions and previous studies. The results show that flexible three-sided culverts at a shallow depth considerably amplify the spectral acceleration and Arias intensity. Larger racking deformation and rocking rotation are also predicted for the three-sided culverts, but the bottom slab influence decreases with increasing burial depth and foundation width. The bottom slab combined with the burial depth and structural stiffness also significantly influences the magnitude and distribution of the dynamic earth pressure. The findings of this work shed light on the critical role of the bottom slab in the seismic responses of box culverts and may have a certain reference value for the preliminary seismic design using R-F relation.

Conditioned duality between supercontinental ‘assembly’ and ‘breakup’ LIPs

A compilation of 178 more precise ages on 10 potential Large Igneous Provinces (LIPs) across southern Africa, is compared to Earth’s supercontinental cycles, where 5 more prominent LIP-events all formed during the assembly of supercontinents, rather than during breakup. This temporal bias is confirmed by a focused review of field relationships, where these syn-assembly LIPs formed behind active continental arcs; whereas, the remaining post-assembly – and likely breakup-related – LIPs never share such associations. Exploring the possibility of two radically different LIP-types, only the two younger breakup events (the Karoo LIP and Gannakouriep Suite) produced basalts with more enriched asthenospheric OIB-signatures; whereas, all assembly LIPs produced basalts with stronger lithospheric, as well as more or less primitive asthenospheric, signatures. A counterintuitive observation of Precambrian breakup LIPs outcropping as smaller fragments that are more peripherally located along craton margins, compared to assembly LIPs as well as the Phanerozoic Karoo breakup LIP, is explained by different preservation potentials during subsequent supercontinental cycles. Thus, further accentuating radical differences between (1) breakup LIPs, preferentially intruding along what evolves to become volcanic rifted margins that are more susceptible to deformation within subsequent orogens, and (2) assembly LIPs, typically emplaced along back-arc rifts within more protected cratonic interiors. A conditioned duality is proposed, where assembly LIPs are primarily sustained by thermal blanketing (as well as local arc hydration and rifting) below assembling supercontinents and breakup LIPs more typically form above impinging mantle plumes. Such a duality is further related to an overall dynamic Earth model whereby predominantly supercontinent-orientated ocean lithospheric subduction establishes/revitalizes large low shear velocity provinces (LLSVPs) during assembly LIP-activity, and heating of such LLSVPs by the Earth’s core subsequently leads to a derivation of mantle plumes during supercontinental breakup.

Sedimentary logics and the Rohingya refugee camps in Bangladesh

This paper adopts a geosocial approach to sociopolitical research by thinking with sediment as a forceful mode of terraqueous mobility driven by interactions between dynamic earth systems inflected by social processes. It demonstrates that sediment is an active and vital state of matter, with the potential to erupt into and disrupt human politics. Unpacking sediment as a form of movement challenges assumptions of the earth as a stable platform on which socio-political processes play out. The paper develops its argument through analyses of the Rohingya refugee camps in southeast Bangladesh and a char (sediment) island in the Meghna Estuary to which Bangladesh proposes to relocate the refugees. In the first situation, the sedimentary logics of anticline geology, deforestation and monsoon rains push back against political agendas directed towards constraining refugee movement. In the second, fluvial and oceanic sedimentary dynamics and the post-Holocene volatility of the monsoon throw into doubt the engineering solution proposed by Bangladesh to the political problems the refugee presence poses. Through these examples, the paper adds to literature on how states of matter inflect, exceed, undercut or in other ways interfere with matters of state through their unique, dynamic environmental properties.

New insights into seismic absorption imaging

In recent years, attenuation has been used as a marker for source and dynamic Earth processes due to its higher sensitivity to small variations of lithospheric properties compared to seismic velocity. From seismic hazard analysis to oil and gas exploration and rock physics, many fields need a better reconstruction of energy absorption, a constituent of seismic attenuation generally considered a reliable marker of fluid saturation in space. Here, we propose absorption tomography (AT), a technique grounded on the principles of scattering tomography and Multiple Lapse Time Window Analysis. We benchmark its efficiency to image absorption in space by comparing its results with those obtained using two of the most common mapping strategies, regionalization and kernel-based inversion for a diffusive regime. We applied these methodologies to three datasets, each characterized by a different tectonic setting and quality of the dataset: the Pollino fault area (Southern Italy), Mount St. Helens Volcano (USA) and Vrancea (Romania). AT overcomes the assignment of a single coda quality factor value between each source-receiver pair by modelling and inverting for the spatial distribution of energy as a function of different lapse times. It can then reconstruct node-dependent envelopes using analytic and computational sensitivity kernels and solve for coda attenuation with a grid-search approach. AT allows for a better reconstruction of the localized absorption anomalies than standard methodologies, even if the efficiency of the technique depends on the quality of the dataset, and identifies outliers in the data that could alter the final result and its interpretation. The implementation of analytical diffusive kernels in AT allows for a fast and highly-resolved imaging of well-sampled seismic faults structures. While slightly reducing resolution on faults and being computationally more expensive, implementing multiple-scattering lapse-time-dependent kernels still provides satisfactory results as well as a more physically-correct forward model.

Sustained Antarctic Research: A 21st Century Imperative

The view from the south is, more than ever, dominated by ominous signs of change. Antarctica and the Southern Ocean are intrinsic to the Earth system, and their evolution is intertwined with and influences the course of the Anthropocene. In turn, changes in the Antarctic affect and presage humanity's future. Growing understanding is countering popular beliefs that Antarctica is pristine, stable, isolated, and reliably frozen. An aspirational roadmap for Antarctic science has facilitated research since 2014. A renewed commitment to gathering further knowledge will quicken the pace of understanding of Earth systems and beyond. Progress is already evident, such as addressing uncertainties in the causes and pace of ice loss and global sea-level rise. However, much remains to be learned. As an iconic global “commons,” the rapidity of Antarctic change will provoke further political action. Antarctic research is more vital than ever to a sustainable future for this One Earth.

Sand–scrap tyre chip mixtures for improving the dynamic behaviour of retaining walls

ABSTRACT This paper presents the dynamic response of retaining wall models backfilled with different types of sand–tyre chips (STC) mixtures using shaking table tests. The STC mixtures with different tyre chips proportions, such as STC10, STC20, STC30, STC40, STC50 and STC0 (control test) were considered as backfill materials. A 600 mm retaining wall that is produced in a box this is certainly anchored on a shaking table that will produce dynamic excitations. According to the tyre chips content in sand, up to 50% to 65% reduction in wall displacements and 70% to 80% lowering of dynamic earth pressures were observed. The exploratory study reveals the seismic actions of a retaining wall with STC30 backfill over an retaining wall using conventional backfill.

Assessment of Soil Tunnel Interaction in Sand Soil

In this study, series of shaking table tests were carried out to investigate the effect of tunnel model depth and direction of ground acceleration on the ground surface settlement and the dynamic earth pressure on the tunnel wall. Box tunnel model is embedded in dry and saturated soil (Karbala Sand). It subjected to three input sinusoidal motions 0.05g, 0.1g, and 0.2g. Two relative densities were used, 30% for the upper layer and 70% for the lower layer. The results obtained indicate that the settlement of soil surface increases with an increase in ground acceleration. The increase in tunnel model depth leads to an increase in settlement especially at 0.2g earthquake loading (for saturated and dry soil). The change of direction of seismic loading leads to a small change in the settlement for dry soil. The results appear that dynamic earth pressure (DEP) was positive in dry soil and negative in saturated soil in all test. In saturated soil, the effect of direction of ground acceleration and depth of tunnel model on DEP in 0.2g is quite little.

Compositional characteristics of the MORB mantle and bulk silicate earth based on spinel peridotites from the Tariat Region, Mongolia

A new collection of spinel-peridotite xenoliths from Quaternary basaltic centers in the Tariat region of Mongolia provide a sample of the shallow lithospheric mantle beneath this area. Ninety-seven of these xenoliths were analyzed for whole rock and mineral major element composition. Both orthopyroxenes and clinopyroxenes separated from the samples were analyzed for trace element content. For a selection of samples, whole rocks were analyzed for trace element contents and clinopyroxenes for the isotopic composition of Sr, Nd, Hf, and Pb. A number of the whole rocks also were analyzed for their Re-Os systematics. Mineral thermometry provides equilibration temperatures in the range of 858–1073 °C that places the origin of these samples in the shallow upper mantle just below the crust of this region. Over half of the samples have fertile major element compositions with Al2O3 concentrations between 3.5 and 4.5 wt%. About a third of the samples are more refractory, yet show enrichment in highly incompatible elements suggestive of recent metasomatism that is hosted both by major minerals and interstitial materials. About 10% of the samples show the compositional consequences of having experienced addition of cumulates from mafic melts in the mantle, including composite samples with pyroxenite and peridotitic portions. The fertile peridotite xenoliths from the Tariat region are samples of mantle that is compositionally and isotopically similar to that which supplies modern mid-ocean ridge basalt (MORB) volcanism. While the major element compositions of the majority of these samples approach the composition estimated for the Bulk-Silicate-Earth (BSE), the peridotites with fertile major element chemistry all show a slight degree of depletion in the more highly incompatible elements and have radiogenic isotopic compositions (87Sr/86Sr mostly from 0.7021 to 0.7035, eNd from +5.6 to +11.0 and eHf from +12.0 to +18.5) consistent with small volume melt removal in the mid-Proterozoic. The composition of these xenoliths is well-matched by models that suggest the MORB-source mantle is produced in a dynamic Earth by the many melt extraction events that have built up the continental crust and created a portion of the mantle depleted in the elements that are enriched in continental crust. For this reason, the most obvious petrogenetic explanation for this section of continental lithospheric mantle is that it is essentially undifferentiated MORB-source mantle that was accreted beneath the Paleozoic crust of this region during the ocean-closing events that formed the Central Asian Orogenic Belt. The composition of these xenoliths provides an opportunity to examine details of estimates for the composition of both the depleted mantle sources of MORB and the BSE. The Tariat xenoliths clearly support the observation that the MORB mantle is unexpectedly depleted in Nb, Ta, and possibly Ti compared to models that create the MORB mantle by extraction of continental crust. Given these characteristics, the Tariat xenoliths, though sampled in the middle of Earth’s largest continent, may provide the least altered look at the composition of the upper mantle that provides volcanism along the world’s ocean ridges.

Shaking table test on the seismic response of large-scale subway station in a loess site: A case study

More and more underground infrastructures have been built in special soil in recent years, especially in the loess area of western China. The loess, as a special soft soil, can have particular influence on the seismic characteristics of underground structures. Therefore, the seismic performance and safety evaluation of underground structures in loess area should be concerned. A series of large-scale shaking table tests were performed to investigate the damage mechanisms of a frame-type subway station structure in a loess site. The test results showed that the model soil softening and the stiffness degradation of the soil-structure system were more serious under stronger input motions. The acceleration response of the soil-structure interaction system in a loess site was more like that of a free-field when input PGA is lower. However, the soil-structure interaction phenomenon was more remarkable both in horizontal and vertical direction when higher PGA was input. The dominant frequency of the input motion had an inverse effect on the lateral soil deformation. The direct-force action mode of the dynamic earth pressure acting on underground structures presents a trumpet-type distribution. Meanwhile, the soil-structure interaction exhibited complex mechanical behavior, and slipping or gapping in test cases with higher PGA may occur. The strain measured in the center pillar and middle slab of the subway station was larger than that in other components. The results provide an insight into how strong ground motion might induce the influence and a possible way to describe quantitatively the damage of subway structure in loess ground.