Regional-scale controls on rockfall occurrence

Rockfalls exert a first-order control on the rate of rock wall retreat on mountain slopes and on coastal rock cliffs. Their occurrence is conditioned by a combination of intrinsic (resisting) and extrinsic (driving) processes, yet determining the exact effects of these processes on rockfall activity and the resulting cliff erosion remains difficult. Although rockfall activity has been monitored extensively in a variety of settings, high-resolution observations of rockfall occurrence on a regional scale are scarce. This is partly owing to difficulties in adequately quantifying the full range of possible rockfall volumes with sufficient accuracy and completeness, and at a scale that exceeds the influence of localised controls on rockfalls. This lack of insight restricts our ability to abstract patterns, to identify long-term changes in behaviour, and to assess how rock slopes respond to changes in both structural and environmental conditions, without resorting to a space for-time substitution. This thesis develops a workflow, from novel data collection to analysis, which is tailored to monitoring rockfall activity and the resulting cliff retreat continuously (in space), in 3D, and over large spatial scales $(> 10^4 m)$. The approach is tested by analysing rockfall activity and the resulting erosion recorded along 20.5 km of near-vertical coastal cliffs, in what is considered as the first multi-temporal detection of rockfalls at a regional-scale and in full 3D. The resulting data are then used to derive a quantitative appraisal of along-coast variations in the geometric properties of exposed discontinuity surfaces, to assess the extent to which these drive patterns in the size and shape of the rockfalls observed. High-resolution field monitoring is then undertaken along a subsection of the coastline $(> 10^2 m)$, where cliff lithology and structure are approximately uniform, in order to quantify spatial variations in wave loading characteristics and to relate these to local morphological conditions, which can act as a proxy for wave loading characteristics. The resulting rockfall inventory is analysed to identify the characteristics of rock slope change that only become apparent when assessed at this scale, placing bounds on data previously collected more locally $(< 10^2 m)$. The data show that spatial consistencies in the distribution of rockfall shape and volume through time approximately follow the geological setting of the coastline, but that variations in the strength of these consistencies are likely to be conditioned by differences in local processes and morphological controls between sites. These results are used to examine the relationships between key metrics of erosion, structural, and morphological controls, which ultimately permits the identification of areas where patterns of erosion are dominated by either intrinsic or extrinsic processes, or a mixture of both. Uniquely, the methodologies and data presented here mark a step-change in our ability to understand the competing effects of different processes in determining the magnitude and frequency of rockfall activity, and the resulting cliff erosion. The findings of this research hold considerable implications for our understanding of rockfalls, and for monitoring, modelling, and managing actively failing rock slopes

Mining Safety and Sustainability I

Safety and sustainability are becoming ever bigger challenges for the mining industry with the increasing depth of mining. It is of great significance to reduce the disaster risk of mining accidents, enhance the safety of mining operations, and improve the efficiency and sustainability of development of mineral resource. This book provides a platform to present new research and recent advances in the safety and sustainability of mining. More specifically, Mining Safety and Sustainability presents recent theoretical and experimental studies with a focus on safety mining, green mining, intelligent mining and mines, sustainable development, risk management of mines, ecological restoration of mines, mining methods and technologies, and damage monitoring and prediction. It will be further helpful to provide theoretical support and technical support for guiding the normative, green, safe, and sustainable development of the mining industry

The Relationship Between Oceanic Transform Fault Segmentation, Seismicity, and Thermal Structure

Mid-ocean ridge transform faults (RTFs) are typically viewed as geometrically simple, with fault lengths readily constrained by the ridge-transform intersections. This relative simplicity, combined with well-constrained slip rates, make them an ideal environment for studying strike-slip earthquake behavior. As the resolution of available bathymetric data over oceanic transform faults continues to improve, however, it is being revealed that the geometry and structure of these faults can be complex, including such features as intra-transform pull-apart basins, intra-transform spreading centers, and cross-transform ridges. To better determine the resolution of structural complexity on RTFs, as well as the prevalence of RTF segmentation, fault structure is delineated on a global scale. Segmentation breaks the fault system up into a series of subparallel fault strands separated by an extensional basin, intra-transform spreading center, or fault step. RTF segmentation occurs across the full range of spreading rates, from faults on the ultraslow portion of the Southwest Indian Ridge to faults on the ultrafast portion of the East Pacific Rise (EPR). It is most prevalent along the EPR, which hosts the fastest spreading rates in the world and has undergone multiple changes in relative plate motion over the last couple of million years. Earthquakes on RTFs are known to be small, to scale with the area above the 600°C isotherm, and to exhibit some of the most predictable behaviors in seismology. In order to determine whether segmentation affects the global RTF scaling relations, the scalings are recomputed using an updated seismic catalog and fault database in which RTF systems are broken up according to their degree of segmentation (as delineated from available bathymetric datasets). No statistically significant differences between the new computed scaling relations and the current scaling relations were found, though a few faults were identified as outliers. Finite element analysis is used to model 3-D RTF fault geometry assuming a viscoplastic rheology in order to determine how segmentation affects the underlying thermal structure of the fault. In the models, fault segment length, length and location along fault of the intra-transform spreading center, and slip rate are varied. A new scaling relation is developed for the critical fault offset length (OC) that significantly reduces the thermal area of adjacent fault segments, such that adjacent segments are fully decoupled at ∼4OC . On moderate to fast slipping RTFs, offsets ≥ 5 km are sufficient to significantly reduce the thermal influence between two adjacent transform fault segments. The relationship between fault structure and seismic behavior was directly addressed on the Discovery transform fault, located at 4°S on the East Pacific Rise. One year of microseismicity recorded on an OBS array, and 24 years of Mw ≥ 5.4 earthquakes obtained from the Global Centroid Moment Tensor catalog, were correlated with surface fault structure delineated from high-resolution multibeam bathymetry. Each of the 15 Mw ≥ 5.4 earthquakes was relocated into one of five distinct repeating rupture patches, while microseismicity was found to be reduced within these patches. While the endpoints of these patches appeared to correlate with structural features on the western segment of Discovery, small step-overs in the primary fault trace were not observed at patch boundaries. This indicates that physical segmentation of the fault is not the primary control on the size and location of large earthquakes on Discovery, and that along-strike heterogeneity in fault zone properties must play an important role

On the physical interaction between ocean waves and coastal cliffs

Wave impacts have long been posited as the primary forcing mechanism of coastal cliff recession. Recent developments in the study of hydrodynamics at coastal structures such as seawalls and breakwaters have shown that wave pressures are stochastic in nature and have a broad range of first- and second-order controls. This understanding has yet to be translated to coastal cliffs, where it is still largely assumed that wave impact characteristics can be predicted by simple deterministic formulae. Hydraulic components in coastal models are limited by the lack of in-situ measurements of waves at the cliff toe due to the difficulties in deploying instrumentation in such energetic and inaccessible environments. To address this, I have approached the problem threefold. Monthly high-resolution terrestrial laser scanning (TLS) was undertaken over a year at multiple sites at Staithes, North Yorkshire, to evaluate the recession rate and detachment characteristics of the lower cliff section. Concurrently, wave gauges were deployed at the cliff toe of each site to monitor wave conditions. A novel method of measuring wave impacts was undertaken at one of the sites for nine low-to-low tidal cycles. New and established methods for processing this data were used. Analysis of the erosion dataset revealed distinct temporal patterns of erosion, with accelerated erosion rates during winter. Vertical variations in detachment volumes below 0.1 m3 related to the tidal elevation were also observed, suggesting a key marine influence. Detachment frequency and volume were found to be influenced by lithology type and joint density. Wave conditions over the study period were found to be depth-limited, yet some waves at the toe were found to be larger than those offshore due to shoaling. Wave breaking conditions were strongly influenced by platform morphology and tidal stage. Up to 9% of all waves were breaking on impact. Measurements of wave impacts revealed approximately 14% of wave exhibited high-magnitude impulsive pressures generated by breaking and broken waves. These were analysed probabilistically and found to be controlled primarily by the ratio between wave height and water depth. These data were used to develop a conceptual model of forcing at the cliff toe, including an evaluation of the ability of waves to remove material via enhanced pressure inside discontinuities and fragmentation of weathered material. These results have broad implications concerning the process geomorphology of rock coasts and the evaluation of wave forcing in coastal models

Global multiple-frequency seismic tomography using teleseismic and core-diffracted body waves

Seismic tomography is the pre-eminent tool for imaging the Earth's interior. Since the advent of this method in the 1980's, the internal structure of Earth has been vastly sampled and imaged at a variety of scales, and the resulting models have served as the primary means to investigate the processes driving our planet. Significant recent advances in seismic data acquisition and computing power have drastically progressed tomographic methods. Broad-band seismic waveforms can now be simulated up to the highest naturally occurring frequencies and consequently, measurement techniques can exploit seismic waves in their entire usable spectrum and in multiple frequencies. This dissertation revolves around aspects of global multiple-frequency seismic tomography, from retrieving and processing of large seismological data sets to explore the multi-scale structure of the earth. The centrepiece of this work is an efficient processing strategy to assemble the largest possible data sets for waveform-based tomographic inversions. Motivated by the complex but loosely-constrained structure of the lowermost mantle, we aim to increase the spatial resolution and coverage of the mantle in all depths by extracting a maximum of information from observed seismograms. We first present a method that routinely measures finite-frequency traveltimes of Pdiff waves by cross-correlating observed waveforms with synthetic seismograms across the broad-band frequency range. Large volumes of waveform data of ~ 2000 earthquakes are retrieved and pre-processed using fully automatic software built for this purpose. Synthetic seismograms for these earthquakes are calculated by semi-analytical wave propagation through a spherically symmetric earth model, to 1 Hz dominant frequency. This way, we construct one of the largest core-diffracted P wave traveltime collections so far with a total of 479,559 traveltimes in frequency passbands ranging from 30.0 to 2.7 s dominant period. Projected onto their core-grazing ray segments, the Pdiff observations recover major structural, lower-mantle heterogeneities known from existing global mantle models. An inversion framework with adaptive parameterisation and locally-adjusted regularisation is developed to accurately map the information of this data set onto the desired model parameters. This broad-band waveform inversion seamlessly incorporates the Pdiff measurements alongside a very large data set of conventional teleseismic P and PP measurements. We obtain structural heterogeneities of considerable detail in all mantle depths. The mapped features confirm several previously imaged structures. At the same time, sharper outlines for several subduction systems (e.g., Tethyan, Aegean and Farallon slabs) and uprising mantle plumes (e.g., Iceland, Afar and Tristan da Cunha) appear in our model. We trace some of these features throughout the mantle to investigate their morphological characteristics in a large (whole-mantle) context. Moreover, we report the structural findings revealed by our model. This ranges from geometries of slab complexes and subdivisions of Large Low Shear Velocity Provinces at the root of the mantle to tomographic evidence to support the existence of deep-mantle plumes beneath Iceland and Tristan da Cunha

Interpretation of fracture mechanisms in ductile and brittle materials by the Acoustic Emission Technique

Nowadays, the measure of the damage phenomena inside a structure is a complex problem that requires the use of innovative Structural Health Monitoring (SHM) and non-destructive investigation methodologies. The non-destructive method based on the Acoustic Emission (AE) technique has proved highly effective, especially to predict fracture behavior that take place inside a material subjected to mechanical loading. Objective of the research is to use the Acoustic Emission monitoring to evaluate the fracture propagation process during tensile tests, three-point bending (TPB) tests and compression tests. The most representative AE parameters have been measured by sensors in order to obtain detailed information on the wave propagation velocity, signals localization as well as on the dominant fracture mode. As a matter of fact, the waves frequency and the Rise Angle are used to discriminate the prevailing cracking mode from pure opening or sliding. Moreover, the cumulated number of AE events and their amplitude are used to compute the signal energy. For the three-point bending tests on concrete beams, the energy dissipated to create the fracture surfaces and the energy emitted and detected by the AE sensors have been compared on the basis of their cumulative value at the end of the test and their rate during the process loading, in order to investigate on their correlation. A numerical simulation of the mechanical response of the TPB tests has been also performed on the basis of the cohesive crack model. This approach has permitted to obtain a step-by-step evaluation of the crack propagation and a more detailed analysis of the mechanical energy dissipation rate during the loading test. In addition, a dedicated in-situ monitoring at the San Pietro - PratoNuovo gypsum quarry located in Murisengo (AL) - Italy, is started and it is still in progress, developing the application aspects of the AE technique, which has been widely studied from a theoretical and experimental point of view by some Authors in the safeguard of civil and historical buildings. Preliminary laboratory compression tests on gypsum specimens with different slenderness (λ=0.5, λ=1, λ=2) were conducted to assess the validity and efficiency of the system in view to a permanent installation for in-situ monitoring. Currently the quarry is subjected to a multiparameter monitoring, by the AE technique and the detection of the environmental neutron field fluctuations, in order to assess the structural stability and, at the same time, to evaluate the seismic risk of the surrounding area

Insights into temperature controls on rockfall occurrence and cliff erosion

A variety of environmental triggers have been associated with the occurrence of rockfalls however their role and relative significance remains poorly constrained. This is in part due to the lack of concurrent data on rockfall occurrence and cliff face conditions at temporal resolutions that mirror the variability of environmental conditions, and over durations for large enough numbers of rockfall events to be captured. The aim of this thesis is to fill this data gap, and then to specifically focus on the role of temperature in triggering rockfall that this data illuminates. To achieve this, a long-term multiannual 3D rockfall dataset and contemporaneous Infrared Thermography (IRT) monitoring of cliff surface temperatures has been generated. The approaches used in this thesis are undertaken at East Cliff, Whitby, which is a coastal cliff located in North Yorkshire, UK. The monitored section is ~ 200 m wide and ~65 m high, with a total cliff face area of ~9,592 m². A method for the automated quantification of rockfall volumes is used to explore data collected between 2017–2019 and 2021, with the resulting inventory including > 8,300 rockfalls from 2017–2019 and > 4,100 rockfalls in 2021, totalling > 12,400 number of rockfalls. The analysis of the inventory demonstrates that during dry conditions, increases in rockfall frequency are coincident with diurnal surface temperature fluctuations, notably at sunrise, noon and sunset in all seasons, leading to a marked diurnal pattern of rockfall. Statistically significant relationships are observed to link cliff temperature and rockfall, highlighting the response of rock slopes to absolute temperatures and changes in temperature. This research also shows that inclement weather constitutes the dominant control over the annual production of rockfalls but also quantifies the period when temperature controls are dominant. Temperature-controlled rockfall activity is shown to have an important erosional role, particularly in periods of iterative erosion dominated by small size rockfalls. As such, this thesis provides for the first high-resolution evidence of temperature controls on rockfall activity, cliff erosion and landform development

Insights into Rockfall from Constant 4D Monitoring

Current understanding of the nature of rockfall and their controls stems from the capabilities of slope monitoring. These capabilities are fundamentally limited by the frequency and resolution of data that can be captured. Various assumptions have therefore arisen, including that the mechanisms that underlie rockfall are instantaneous. Clustering of rockfall across rock faces and sequencing through time have been observed, sometimes with an increase in pre-failure deformation and pre-failure rockfall activity prior to catastrophic failure. An inherent uncertainty, however, lies in whether the behaviour of rockfall monitored over much shorter time intervals (Tint) is consistent with that previously monitored at monthly intervals, including observed failure mechanisms, their response to external drivers, and pre-failure deformation. To address the limitations of previous studies on this topic, 8 987 terrestrial laser scans have been acquired over 10 months from continuous near-real time monitoring of an actively failing coastal rock slope (Tint = 0.5 h). A workflow has been devised that automatically resolves depth changes at the surface to 0.03 m. This workflow filters points with high positional uncertainty and detects change in 3D, with both approaches tailored to natural rock faces, which commonly feature sharp edges and partially occluded areas. Analysis of the resulting rockfall inventory, which includes > 180 000 detachments, shows that the proportion of rockfall < 0.1 m3 increases with more frequent surveys for Tint < ca. 100 h, but this trend does not continue for surface comparison over longer time intervals. Therefore, and advantageously, less frequent surveys will derive the same rockfall magnitude-frequency distribution if captured at ca. 100 h intervals as compared to one month or even longer intervals. The shape and size of detachments shows that they are more shallow and smaller than observable rock mass structure, but appear to be limited in size and extent by jointing. Previously explored relationships between rockfall timing and environmental and marine conditions do not appear to apply to this inventory, however, significant relationships between rockfall and rainfall, temperature gradient and tides are demonstrated over short timescales. Pre-failure deformation and rockfall activity is observed in the footprint of incipient rockfall. Rockfall activity occurs predominantly within the same ca. 100 h timescale observed in the size-distribution analysis, and accelerated deformation is common for the largest rockfall during the final 2 h before block detachment. This study provides insights into the nature and development of rockfall during the period prior to detachment, and the controls upon it. This holds considerable implications for our understanding of rockfall and the improvement of future rockfall monitoring

Multiscale Modeling of the European aeromagnetic field

In this research, the aim of the study is the interpretation of the main magnetic anomalies at the European scale. Being the field characterized by anomalies originating by sources at different depth within the crust, a multiscale approach is the most suitable method to take into account all the different components of the anomaly field. In fact, at different altitudes, say from 5 km to 350 km, the anomaly field is varies and there is no specific scale, which can be judged as the most relevant for the analysis. The multiscale analysis of aeromagnetic data is based on a multiscale dataset, which is generated by the upward continuation of the dataset of the European and Mediterranean Magnetic Project up to satellite altitudes. The interpretation of the magnetic anomalies was carried out following two main steps: a) producing the total gradient maps of the magnetic field at low and high altitudes, in order to identify the magnetic features through the whole crust. This technique has been particularly useful because of three main properties: i) the anomalies of the total gradient modulus are monopolar, so losing the dipolar aspect of the magnetic field, regardless the source and field magnetization directions; ii) the maxima of the total gradient modulus are placed above the source position, regardless of the source and field magnetization directions; iii) the areas where it reaches very low values may be safely regarded as regions with a low-magnetization crust; conversely magnetic lows of the magnetic field are not exclusively linked to low-magnetization areas, but depends mainly on the total magnetization of the sources, either normally or reversely magnetized. Our total gradient analysis showed that the origin of the Central European Magnetic Low (CEML) should be attributed to the strong differences in magnetization between the central European crust and the North-Eastern platform. However, due to the property i) some reversely magnetized sources were detected, in different regions of central Europe (Anglo-Brabant Massif, Bohemian Massif, Pannonian basin). b) using specific multiscale tools for the simultaneous interpretation of the field at many scales. In particular, the Multiridge method allows the multiscale magnetic field to be interpreted in terms of source depths and shape. By this method, a model is obtained of the crustal magnetic sources beneath the TESZ, the Bohemian Massif and the Adriatic magnetic anomalies, which are key anomalies for the magnetic field in Europe, no matter the altitude. In order to estimate the deepest source depths in the TESZ region, the Multiridge method was applied to the large scales (50-100 km altitude), obtaining a set of singular points at depths ranging between 35-40 km. Considering the trend of the heat flow and the geological models around the study areas, a meaningful correspondence was found among the location of the estimated singular points and the most abrupt variations and complex morphology features of the magnetic basement and the Moho boundary. The interpreted models are largely in agreement with geological models based on seismic surveys and contribute to the whole knowledge of the areas, since refer to a wider region, if compared to that covered by seismic. Multiscale methods contribute to a complete knowledge of the area since they refer to the wider region, when compared with that covered by the seismic models