Tsunamis in south central Chile : evidence from coastal lakes

The south central Chilean coast lies on the Peru-Chile subduction zone. As a result, the area is prone to megathrust earthquakes. The convergent motion of the oceanic Nazca Plate and the South American Plate during these earthquakes causes co-seismic vertical deformation on the seafloor, which in turn generates tsunamis. The tsunamis propagate across the Pacific Ocean and eventually inundate the South American and other coasts, where they sometimes cause catastrophic damage. Alongside the destruction of infrastructure and the loss of life, tsunamis deposit distinct sediments. This thesis focuses on tsunami deposits in two coastal lakes, Lake Cucao and Lake Huelde, on the west coast of Isla de Chiloé, south central Chile (42.6° S), and their immediate surroundings. The thesis establishes the sedimentary characteristics of the most recent tsunami deposit in the lakes' sedimentary records. The tsunami in question was caused by the AD 1960 Great Chilean Earthquake (M\textsubscript{W} 9.5). The AD 1960 tsunami inundated both lakes, which are located \textasciitilde{}2 km apart and \textasciitilde{}1.2 km behind the present coastline. The stratigraphy of both lakes features gyttja, interrupted by the abrupt emplacement of a sandy layer with mud rip-up clasts and a mud cap. This sandy layer reflects a sudden change in the sedimentary environment. Using grain size analysis and comparisons with samples from modern environments, it is demonstrated that the proximal (seaward) part of the tsunami deposit consists of a mixture of sand derived from subaerial sources and reworked lacustrine gyttja. In the distal (landward) part of Lake Cucao, the tsunami deposit lacks the sand component and consists entirely of remobilised lake sediments. The repetition of tsunami deposit sequences (or subsets thereof) in Lake Huelde suggests a minimum of three inundating waves. Sub-bottom profiles and side scan sonar mosaics reveal tsunami inundation over the barrier and more prominently through the outlet river channel. The dominant role of the river channel as a pathway for sediment transport is also described in core samples by tsunami deposits that are fining away from the channel mouth. The identification and description of the AD 1960 deposit provide important insights into tsunami sedimentation in coastal lakes and set a baseline as to what tsunami deposits should look like in the deeper sedimentary record of the two coastal lakes. In Lake Huelde, the established expectation of the sedimentary characteristics of tsunami deposits is used to investigate the exceptionally long and continuous sedimentary record. Lake Huelde's sedimentary record contains 17 distinct detrital layers from the last 5500 yrs, which are interpreted as tsunami deposits. With the unusually high number of tsunami deposits in a single sedimentary record it is possible to analyse the recurrence pattern. Recurrence rates and pattern are an integral part to tsunami hazard assessment. In probabilistic tsunami hazard assessment tsunami recurrences are typically modelled with a Poisson distribution, which, as I demonstrate, does not necessarily represent the hazard correctly. Results of \textsuperscript{137}Cs- and \textsuperscript{210}Pb-dating, infrared stimulated luminescence (IRSL) dating and radiocarbon dating are used as input for Bayesian age-depth modelling. The resulting age-depth relationship is used to estimate the age of tsunami deposits. The inferred mean recurrence time of \textasciitilde{}325 yrs broadly agrees with the existing regional paleoseismic and paleotsunami records. However, our record reveals a large temporal variability between tsunami events, which forms a bimodal probability density function for the recurrence pattern with modes at \textasciitilde{}115 and \textasciitilde{}490 yrs. As the mean recurrence time coincides with the lowest probability between the two modes, I conclude that the sense of safety in coastal communities in south central Chile, 55 yrs after the last catastrophe, may be deceiving. A tsunamigenic earthquake in the near future would not redefine the extremes of the presented record. Lake Cucao's sedimentary history is more complex than Lake Huelde's, however, its sedimentary record holds valuable paleotsunami information, too. The area of the lake basin has been submerged since the postglacial sea-level rise and may have recorded tsunami inundations in its sedimentary record since then. A radiocarbon date from a sediment core and internal acoustic reflections, which converge towards a tidal channel, indicate that tidal currents were active at least sporadically over the last 3700 yrs. Little vertical displacement over the last 3700 yrs maintained the ability of Lake Cucao to record tsunamis in its sedimentary record. In total 15 detrital layers are interpreted as tsunami deposits with a varying level of confidence. The level of confidence depends on five criteria; there are site-specific criteria, i.e. i) high magnetic susceptibility of the sediment indicating high detrital content in contrast to the organic-rich gyttja, ii) core-to-core correlation, and iii) acoustic reflection correlation to the sedimentary record (the latter two indicate traceability of the detrital layer in the sedimentary record), and general criteria, i.e. iv) presence of mud clasts indicating an episode of extreme flow conditions in an otherwise calm environment and v) age correlation to known paleotsunamis in the area. The neighbouring Lake Huelde contains 14 or 15 tsunami deposits in the same time interval as Lake Cucao, suggesting that both lakes may have been equally reliable in recording tsunami inundation. This study adds a long paleotsunami record on a coastline, where extreme tsunamis occur relatively frequently and where long paleotsunami records are still sparse. Many important sedimentary features were revealed by side scan sonar data and sub-bottom profiles, which demonstrates how indispensible acoustic imagery can be in understanding the depositional environment, especially in lakes as dynamic as the coastal Lake Cucao. Imaging tsunami deposits in coastal lakes with sidescan sonars and sub-bottom profiles can now be added to the growing list of tools in the toolkit to observe, describe and recognise tsunami deposits. The amount of data collected about the numerous tsunami deposits in both lakes allows a ranking of tsunami deposits according to multiple criteria, which may represent the size of the associated tsunami. These criteria are i) maximum magnetic susceptibility, ii) average magnetic susceptibility, iii) traceability (lateral extent), iv) average tsunami deposit thickness and v) percentage of mud rip-up clast intervals. Integrating the two coastal lake records, it is evident that the AD 1960 tsunami was one of the major events in both lakes in the last \textasciitilde{}4000 yrs. Two older tsunami deposits of similar characteristics as the AD 1960 tsunami deposit are tentatively correlated across both lakes. Their ages are \textasciitilde{}3740 and \textasciitilde{}3890 cal. yrs BP. However, the relative ranking of tsunamis only compares the sedimentary effect in both lakes and cannot be translated directly to relative tsunami size, because environmental changes are not accounted for. For example, landscape evolution, horizontal and vertical shoreline displacement all affect how and where an environment records a tsunami inundation. Models that could quantify the tsunami size in absolute terms need this information. These models can be physical or numerical, however, physical models of tsunamis focus on subaerial landslide-induced tsunamis. Of the numerical models, there are forward models and inverse models. Forward models are extremely complex dynamic models and can include all aspects of tsunamis from fault slip simulation during the causative earthquake to vertical seafloor deformation, tsunami generation, propagation and inundation, and eventually erosion and deposition of coastal sediments. Inverse models try to infer tsunami inundation parameters, e.g. flow depth, from characteristics of tsunami deposits. However, none of the existing inverse tsunami models are applicable to tsunami sediments in coastal lakes. Furthermore, only little is known of how the environment changed around Lake Cucao and Lake Huelde, e.g. relative sea-level change, vegetation changes, horizontal shoreline displacement and more. Further investigation towards the environmental history and application of numerical forward models could facilitate quantitative paleotsunami research

Lipolysis on Lipid Droplets: Mathematical Modelling and Numerical Discretisation

Lipolysis is a life-essential metabolic process, which supplies fatty acids stored in lipid droplets to the body in order to match the demands of building new cells and providing cellular energy. In this paper, we present a first mathematical modelling approach for lipolysis, which takes into account that the involved enzymes act on the surface of lipid droplets. We postulate an active region near the surface where the substrates are within reach of the surface-bound enzymes and formulate a system of reaction-diffusion PDEs, which connect the active region to the inner core of lipid droplets via interface conditions. We establish two numerical discretisations based on finite element method and isogeometric analysis, and validate them to perform reliably. For numerical testing purposes, we introduce and analyse a testing model featuring a nontrivial explicit stationary state solution, which describes beside lipolysis also a reverse process (in a physiologically oversimplified way). We prove the unique existence of global and equilibrium solutions. We establish exponential convergence to the equilibrium solutions using the entropy method. We then study the stationary state model and compute explicitly for radially symmetric solutions. Concerning the finite element methods, we show numerically the linear and quadratic convergence of the errors with respect to the $H^{1}$- and $L^{2}$-norms, respectively. Finally, we present numerical simulations of a prototypical PDE model of lipolysis and illustrate that ATGL clustering on lipid droplets can significantly slow down lipolysis.Comment: 27 pages, 18 figure

Emergent Trion-Phonon Coupling in Atomically-Reconstructed MoSe2_2-WSe2_2 Heterobilayers

In low-temperature resonant Raman experiments on MoSe$_2$-WSe$_2$ heterobilayers, we identify a hybrid interlayer shear mode (HSM) with an energy, close to the interlayer shear mode (SM) of the heterobilayers, but with a much broader, asymmetric lineshape. The HSM shows a pronounced resonance with the intralayer hybrid trions (HX$^-$) of the MoSe$_2$ and WSe$_2$ layers, only. No resonance with the neutral intralayer excitons is found. First-principles calculations reveal a strong coupling of Q-valley states, which are delocalized over both layers and participate in the HX$^-$, with the SM. This emerging trion-phonon coupling may be relevant for experiments on gate-controlled heterobilayers.Comment: 6 pages, 3 figure

Sedimentary evidence of the Late Holocene tsunami in the Shetland Islands (UK) at Loch Flugarth, northern Mainland

Tsunami deposits around the North Sea basin are needed to assess the long-term hazard of tsunamis. Here, we present sedimentary evidence of the youngest tsunami on the Shetland Islands from Loch Flugarth, a coastal lake on northern Mainland. Three gravity cores show organic-rich background sedimentation with many sub-centimetre-scale sand layers, reflecting recurring storm overwash and a sediment source limited to the active beach and uppermost subtidal zone. A basal 13-cm-thick sand layer, dated to 426–787 cal. a CE based on 14C, 137Cs and Bayesian age–depth modelling, was found in all cores. High-resolution grain-size analysis identified four normally graded or massive sublayers with inversely graded traction carpets at the base of two sublayers. A thin organic-rich ‘mud’ drape and a ‘mud’ cap cover the two uppermost sublayers, which also contain small rip-up clasts. Grain-size distributions show a difference between the basal sand layer and the coarser and better sorted storm layers above. Multivariate statistical analysis of X-ray fluorescence core scanning data also distinguishes both sand units: Zr, Fe and Ti dominate the thick basal sand, while the thin storm layers are high in K and Si. Enriched Zr and Ti in the basal sand layer, in combination with increased magnetic susceptibility, may be related to higher heavy mineral content reflecting an additional marine sediment source below the storm-wave base that is activated by a tsunami. Based on reinterpretation of chronological data from two different published sites and the chronostratigraphy of the present study, the tsunami seems to date to c. 1400 cal. a BP. Although the source of the tsunami remains unclear, the lack of evidence for this event outside of the Shetland Islands suggests that it had a local source and was smaller than the older Storegga tsunami (8.15 cal. ka BP), which affected most of the North Sea basin.</p

Rapid spin depolarization in the layered 2D Ruddlesden Popper perovskite (BA)(MA)PbI

We report temperature-dependent spectroscopy on the layered (n=4) two-dimensional (2D) Ruddlesden-Popper perovskite (BA)(MA)PbI. Helicity-resolved steady-state photoluminescence (PL) reveals no optical degree of polarization. Time-resolved PL shows a photocarrier lifetime on the order of nanoseconds. From simultaneaously recorded time-resolved differential reflectivity (TR$\Delta$R) and time-resolved Kerr ellipticity (TRKE), a photocarrier lifetime of a few nanoseconds and a spin dephasing time on the order of picoseconds was found. This stark contrast in lifetimes clearly explains the lack of spin polarization in steady-state PL. While we observe clear temperature-dependent effects on the PL dynamics that can be related to structural dynamics, the spin dephasing is nearly T-independent. Our results highlight that spin dephasing in 2D (BA)(MA)PbI occurs at time scales faster than the exciton recombination time, which poses a bottleneck for applications aimingto utilize this degree of freedom

A 1500‐year record of North Atlantic storm flooding from lacustrine sediments, Shetland Islands (UK)

Severe storm flooding poses a major hazard to the coasts of north‐western Europe. However, the long‐term recurrence patterns of extreme coastal flooding and their governing factors are poorly understood. Therefore, high‐resolution sedimentary records of past North Atlantic storm flooding are required. This multi‐proxy study reconstructs storm‐induced overwash processes from coastal lake sediments on the Shetland Islands using grain‐size and geochemical data, and the re‐analysis of historical data. The chronostratigraphy is based on Bayesian age–depth modelling using accelerator mass spectrometry 14 C and 137 Cs data. A high XRF‐based Si/Ti ratio and the unimodal grain‐size distribution link the sand layers to the beach and thus storm‐induced overwash events. Periods with more frequent storm flooding occurred 980–1050, 1150–1300, 1450–1550, 1820–1900 and 1950–2000 ce, which is largely consistent with a positive North Atlantic Oscillation mode. The Little Ice Age (1400–1850 ce ) shows a gap of major sand layers suggesting a southward shift of storm tracks and a seasonal variance with more storm floods in spring and autumn. Warmer phases shifted winter storm tracks towards the north‐east Atlantic, indicating a possible trend for future storm‐track changes and increased storm flooding in the northern North Sea region

Moiré phonons in twisted MoSe 2 –WSe 2 heterobilayers and their correlation with interlayer excitons

Abstract: We report about the investigation of twisted MoSe2 homo- and MoSe2–WSe2 heterobilayers by means of low-frequency Raman spectroscopy (LFRS) and low-temperature micro photoluminescence (µPL). In room-temperature LFRS experiments on both, twisted MoSe2 homobilayers and twisted MoSe2–WSe2 heterobilayers, we observe moiré phonons, i.e. folded acoustic phonon modes due to the moiré superlattice. In the heterobilayers, we can identify moiré phonons of both materials, MoSe2 and WSe2. While the twist angles for the homobilayers are relatively precisely known from the applied tear-and-stack preparation method, the twist angles of the heterobilayers have to be determined via second-harmonic-generation microscopy on monolayer regions of the samples, which has significant uncertainties. We show that by the moiré phonons of the heterobilayers, the relative twist angles can be determined on a local scale with much higher precision. We apply our technique for the investigation of a large area H-type (twist angle θ = 60∘ + δ) MoSe2–WSe2 heterobilayer. These investigations show that spatial regions, which can be identified to be atomically reconstructed (i.e. δ = 0∘) by the observation of an interlayer shear mode in LFRS experiments, exhibit a strong, momentum-allowed interlayer-exciton signal in low-temperature µPL. On the contrary, regions, where moiré phonons are observed, i.e. which can be identified to be rigidly twisted by a misalignment angle in the range of 5°≲|δ|≲6° , exhibit no significant interlayer-exciton signals

Dilute suspensions in annular shear flow under gravity: simulation and experiment

A dilute suspension in annular shear flow under gravity was simulated using multi-particle collision dynamics (MPC) and compared to experimental data. The focus of the analysis is the local particle velocity and density distribution under the influence of the rotational and gravitational forces. The results are further supported by a deterministic approximation of a single-particle trajectory and OpenFOAM CFD estimations of the overcritical frequency range. Good qualitative agreement is observed for single-particle trajectories between the statistical mean of MPC simulations and the deterministic approximation. Wall contact and detachment however occur earlier in the MPC simulation, which can be explained by the inherent thermal noise of the method. The multi-particle system is investigated at the point of highest particle accumulation that is found at 2/3 of the particle revolution, starting from the top of the annular gap. The combination of shear flow and a slowly rotating volumetric force leads to strong local accumulation in this section that increases the particle volume fraction from overall 0.7% to 4.7% at the outer boundary. MPC simulations and experimental observations agree well in terms of particle distribution and a close to linear velocity profile in radial direction

Селянський рух в Харківській губернії (1917–1921 рр.)

Дисертацію присвячено комплексному дослідженню розвитку селянського руху в Харківській губернії в період Української революції 1917–1921 рр. Доведено, що невирішені проблеми у сфері аграрних відносин спричинили селянський рух і розгортання збройного конфлікту на Харківщині у 1917–1921 рр. Порівняно ступінь активної участі у революційних подіях у даному регіоні різних соціальних груп населення. Обґрунтовано тезу, що у період Української революції 1917–1921 рр. представники лівих політичних партій вживали поняття "куркуль" для визначення власників індивідуальних селянських господарств, які бажали зберегти приватну власність на землю й активно захищали свої економічні, політичні та національні права. З'ясовано, що невирішеність національного питання була одним з важливих чинників посилення селянського руху у Харківській губернії. Досліджено взаємозв'язок селянського повстанського руху сусідніх регіонів з селянським рухом у Харківській губернії та встановлено, що найбільш впливовими та популярними серед сільського населення регіону було махновське і "уенерівське" повстанство. Розглянуто процес радикалізації селянського руху у 1917–1921 рр., висвітлено пасивні й активні, нелегальні та легальні форми боротьби селянства за свої економічні, політичні та національні інтереси. Узагальнено наслідки селянського руху