Understanding Seismic Embankment Dam Behavior Through Case Histories

From the lessons learned from past earthquakes, it is noticed that modern embankment dams withstand the design earthquake without significant damages. In spite of this scenario it is important to prevent the occurrence of incidents and accidents of embankment dams during the earthquakes and so a deep understanding of the triggering factors is important. Well documents case histories from many parts of the world related embankment dams behaviour during recent earthquakes were carefully selected and are discussed. Based in the governed factors attention is given to the requirements for materials characterization, modelling, analysis, monitoring and safety evaluation. Ageing effects and rehabilitation of dams are analysed. The risks associated with dam projects are discussed. The benefits and concerns of dams are presented. It is important to develop new ways of thinking and strategies to address the future challenges

The Role of Mineral Composition on the Frictional and Stability Properties of Powdered Reservoir Rocks

The growing hazard of induced seismicity driven by the boom in unconventional resources exploitation is strongly linked to fault activation. We perform laboratory measurements on simulated fault gouges comprising powdered reservoir rocks from major oil and gas production sites in China, to probe the control of mineral composition on fault friction and stability responses during reservoir stimulation. Double direct shear experiments were conducted on gouges with phyllosilicate content ranging from 0 to 30wt.% and grain sizes <150m, at constant normal stresses of 10-40MPa and conditions of room temperature and water saturation. The velocity step and slide-hold-slide sequences were employed to evaluate frictional stability and static healing, respectively. Results indicate that the mineralogy of the gouges exhibit a strong control on the frictional strength, stability, and healing. Phyllosilicate-rich samples show lower frictional strength and higher values of (a-b), promoting stable sliding. For the gouges studied, the frictional strength decreases monotonically with increasing phyllosilicate content, and a transition from velocity weakening to velocity strengthening behavior is evident at 15wt.% phyllosilicates. Intermediate healing rates are common in gouges with higher content of phyllosilicates, with high healing rates predominantly in phyllosilicate-poor gouges. As an indispensable component in reservoir rocks, the carbonates are shown to affect both the frictional stability and healing response. These findings can have important implications for understanding the effects of mineralogy on fault behavior and induced seismic potential in geoengineering activities, particularly in reservoirs in China.National Natural Science Foundation of China [41672268, 41772286]; U.S. Department of Energy (DOE) [DE-FE0023354]6 month embargo; published online: 5 February 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Frictional, transport properties, and microstructures of simulated basalt faults

I terremoti indotti dalle attività antropiche costituiscono una discriminante per il successo delle attività industriali quali l’iniezione di acque reflue, l’estrazione di petrolio e gas naturale, lo sfruttamento di energia geotermica e lo stoccaggio geologico di anidride carbonica. Negli ultimi anni, i basalti hanno catturato l’attenzione dell’industria del settore energetico e della comunità scientifica, a causa della loro vasta diffusione nella litosfera oceanica e della loro capacità di mineralizzare la CO2 “trasformandola in roccia” (New York Times 9/2/2015). Tale proprietà, consente di fatto di sottrarre a lungo termine l’anidride carbonica presente in atmosfera, contribuendo pertanto alla riduzione locale delle emissioni di CO2 di origine antropogenica. Comprendere le proprietà di attrito, meccaniche e idrologiche di faglie e fratture in basalto ha assunto pertanto un'importanza fondamentale, per le dirette implicazioni riguardanti l'enucleazione dei terremoti, la loro propagazione e l'arresto in ambienti geologici dominati dai basalti. Per meglio comprendere le proprietà meccaniche di faglie e fratture in basalto, e in particolare la fase di enucleazione dei terremoti, esperimenti di attrito sono stati realizzati mediante l’apparato biassiale BRAVA e l’apparato di tipo rotativo SHIVA, entrambi installati presso l’Istituto Nazionale di Geofisica e Vulcanologia (INGV, Roma). Invece, per caratterizzare le proprietà di trasporto delle carote di basalto e delle faglie sperimentali, la trasmissività idraulica è stata misurata mediante il permeametro, prima e dopo gli esperimenti di attrito su SHIVA. Sono stati trattati tre principali argomenti seguendo un approccio sperimentale per caratterizzare: 1) le proprietà di resistenza di attrito, stabilità e di healing delle faglie sperimentali in basalto (ovvero, faglie polverizzate e superfici di faglia) in condizioni di umidità atmosferica e in condizioni bagnate, integrando i dati meccanici con quelli microstrutturali (Capitolo 2); 2) le instabilità dell’attrito ed i processi di carbonatazione delle superfici di faglia sperimentali aventi diversi gradi di alterazione, cagionati dall’iniezione di fluidi ricchi in H2O, CO2, misture H2O-CO2, e Argon (Capitolo 3); 3) le variazioni delle proprietà idromeccaniche delle superfici di faglia sperimentali e la loro influenza sul loro comportamento durante l’iniezione di acqua in pressione (Capitolo 4). Per quanto concerne i cilindri cavi descritti nel capitolo 4, l’analisi accurata dello stato di sforzo negli esperimenti di tipo rotativo, ha richiesto lo sviluppo di un modello basato sui dati sperimentali che tenesse conto della geometria cilindrica dei campioni montati su SHIVA, la quale modifica il modo in cui la pressione di fluido influisce sullo sforzo normale efficace agente sulla faglia (Appendice 1). Tutti i test sono stati realizzati a temperatura ambiente, che può emulare le condizioni di temperatura di un sito energetico a bassa entalpia. In questa tesi, complessivamente si osservano valori del coefficiente di attrito statico intorno a μ ~ 0.6 – 0.8, a diverse condizioni che spaziano dall’umidità atmosferica a quelle sovra-idrostatiche, indipendentemente dello stato di alterazione dei basalti e della composizione chimica del fluido iniettato durante gli esperimenti a breve termine (&lt; 60 min). Pertanto, le faglie in basalto sono considerate “forti”, e gli elevati tassi di healing testimoniano la loro abilità di riguadagnare la resistenza al taglio durante il periodo intersismico. Secondariamente, metto in evidenza come la struttura delle faglie controlli le proprietà di rate and state e la stabilità delle stesse: mentre le polveri sono più propense ad enucleare terremoti (ovvero possiedono un comportamento di indebolimento con l’aumento di velocità: velocity weakening) quando, a seguito di processi cataclastici con riduzione della granulometria, la deformazione diventa localizzata lungo zone di deformazione ben sviluppate, al contrario, le superfici di faglia passano a un comportamento di incremento dell’attrito con l’aumentare della velocità (velocity strengthening), a seguito di processi di dilatanza che accompagnano la produzione di detrito durante lo scivolamento. Infine, si è osservato che i cambiamenti nelle proprietà idromeccaniche durante la pressurizzazione di fluido possono diventare dominanti rispetto agli effetti prodotti dai cambiamenti di attrito di secondo ordine predetti dalle leggi di rate. A tale riguardo, ho rilevato un più pronunciato indebolimento idromeccanico, laddove la trasmissività idraulica della faglia è minore. Questa osservazione fornisce un efficace meccanismo per l’indebolimento delle faglie e in ultima istanza, portare all’enucleazione di terremoti anche nelle porzioni faglie in basalto caratterizzate da un comportamento “velocity strengthening”.Earthquakes induced by anthropic activities are a major concern for the success of the industrial operations associated with in-situ underground wastewater injection, oil and gas withdrawals, geothermal energy exploitation, and geological carbon sequestration. Over the last few decades, basalt rocks have drawn heightened attention from the geo-energy industry and the scientific community because of their widespread occurrence in the oceanic lithosphere and their efficiency to act as carbon sinks, thus contributing to locally reduce the CO2 anthropogenic emissions. Given the direct implications for earthquake nucleation, propagation, and arrest in basaltic-dominated environments, understanding the frictional, mechanical, and transport properties of basalts-bearing faults and fractures has become of paramount importance. To gain better insights on the mechanical behavior of basalt-hosted faults, notably the earthquake nucleation phase, friction experiments were performed using the biaxial deformation machine BRAVA and the rotary-shear apparatus SHIVA, both installed at the National Institute of Geophysics and Volcanology (INGV, Rome), Italy. Whereas, to characterize the transport properties of basalt cores and simulated faults, hydraulic transmissivity was measured on the permeameter and before and after friction tests on SHIVA. Three main scientific topics were addressed using an experimental approach: 1) the frictional strength, stability, and healing properties of basalt-built experimental faults (i.e., simulated gouge and bare rock surfaces) under room-dry and wet conditions, by integrating the mechanical data with fault microstructures (Chapter 2); 2) the frictional instabilities and carbonation processes of simulated initially bare rock surfaces with different degree of alteration, triggered by injection of pressurized H2O, pure CO2 , CO2 - rich water, and Argon (Chapter 3); 3) the hydromechanical properties changes of simulated initially bare rock surfaces and their influence on the fault slip behavior during water pressurization (Chapter 4). The accurate stress paths analysis from rotary-shear tests involving hollow bare rock surfaces in Ch.4 required the development of an experimentally derived model accounting for the cylindrical geometry of SHIVA samples, that modifies the fluid pressure contribution on the effective normal stress acting on the laboratory fault, (Appendix 1). All the tests were performed at ambient temperature, which may mimic the temperature conditions in low enthalpy geo-energy sites in basalts. In this dissertation, overall, I demonstrate that the static friction coefficient of basalts is in the range of μ ~ 0.6 – 0.8, at conditions ranging from room-dry to supra-hydrostatic, regardless of the alteration state of basalts and the fluid chemistry during short-term laboratory experiments (&lt; 60 min). Therefore, basalts are inherently frictionally strong and the high healing rates testify their ability to regain shear strength during the interseismic period. Secondly, I show that fault microstructure controls their frictional stability: while simulated gouge are more prone to host earthquake nucleation (i.e., velocity weakening behavior) when deformation becomes localized along well-developed shear zones formed in response to cataclasis and grain size reduction, bare rock surfaces show the opposite behavior, transitioning to velocity strengthening behavior promoted by dilatancy processes coupled with gouge production during shearing. Finally, I illustrate that changes in coupled hydromechanical properties during fluid pressurization can dominate over the effects of second-order frictional changes predicted by the rate-and state-friction laws. In this regard, I observed that hydromechanical weakening effects become more pronounced the lower the fault transmissivity. This evidence provides an effective mechanism for inducing fault weakening and ultimately, to bring about earthquake slip also in velocity-strengthening basalt fault patches

Acoustic Monitoring of Inelastic Compaction in Porous Granular Materials

We study the transition from cohesive to noncohesive granular states of synthetic rocks under oedometric loading, combining simultaneous measurements of ultrasound velocity and acoustic emissions. Our samples are agglomerates made of glass beads bonded with a few percent of cement, either ductile or brittle. These cemented granular samples exhibit an inelastic compaction beyond certain axial stresses likely due to the formation of compaction bands, which is accompanied by a significant decrease of compressional wave velocity. Upon subsequent cyclic unloading and reloading with constant consolidation stress, we found the mechanical and acoustic responses similar to those in noncohesive granular materials, which can be interpreted within the effective medium theory based on the Digby bonding model. Moreover, this model allows P-wave velocity measured at vanishing pressure to be interpreted as an indicator of the debonding on the scale of grain contact. During the inelastic compaction, stick-slip like stress drops were observed in brittle cement-bonded granular samples accompanied by the instantaneous decrease of the P-wave velocity and acoustic emissions which display an Omori-like law for foreshocks, i.e., precursors. By contrast, mechanical responses of ductile cement-bonded granular samples are smooth (without visible stick-slip like stress drops) and mostly aseismic. By applying a cyclic loading and unloading with increasing consolidation stress, we observed a Kaiser-like memory effect in the brittle cement-bonded sample in the weakly damaged state which tends to disappear when the bonds are mostly broken in the non-cohesive granular state after large-amplitude loading. Our study shows that the macroscopic ductile and brittle behavior of cemented granular media is controlled by the local processes on the scale of the bonds between grains.Comment: 22 pages, 15 figure

Earthquakes: from chemical alteration to mechanical rupture

In the standard rebound theory of earthquakes, elastic deformation energy is progressively stored in the crust until a threshold is reached at which it is suddenly released in an earthquake. We review three important paradoxes, the strain paradox, the stress paradox and the heat flow paradox, that are difficult to account for in this picture, either individually or when taken together. Resolutions of these paradoxes usually call for additional assumptions on the nature of the rupture process (such as novel modes of deformations and ruptures) prior to and/or during an earthquake, on the nature of the fault and on the effect of trapped fluids within the crust at seismogenic depths. We review the evidence for the essential importance of water and its interaction with the modes of deformations. Water is usually seen to have mainly the mechanical effect of decreasing the normal lithostatic stress in the fault core on one hand and to weaken rock materials via hydrolytic weakening and stress corrosion on the other hand. We also review the evidences that water plays a major role in the alteration of minerals subjected to finite strains into other structures in out-of-equilibrium conditions. This suggests novel exciting routes to understand what is an earthquake, that requires to develop a truly multidisciplinary approach involving mineral chemistry, geology, rupture mechanics and statistical physics.Comment: 44 pages, 1 figures, submitted to Physics Report

Seismic Response to Injection Well Stimulation in a High-Temperature, High-Permeability Reservoir

Fluid injection into the Earth's crust can induce seismic events that cause damage to local infrastructure but also offer valuable insight into seismogenesis. The factors that influence the magnitude, location, and number of induced events remain poorly understood but include injection flow rate and pressure as well as reservoir temperature and permeability. The relationship between injection parameters and injection-induced seismicity in high-temperature, high-permeability reservoirs has not been extensively studied. Here we focus on the Ngatamariki geothermal field in the central Taupō Volcanic Zone, New Zealand, where three stimulation/injection tests have occurred since 2012. We present a catalog of seismicity from 2012 to 2015 created using a matched-filter detection technique. We analyze the stress state in the reservoir during the injection tests from first motion-derived focal mechanisms, yielding an average direction of maximum horizontal compressive stress (SHmax) consistent with the regional NE-SW trend. However, there is significant variation in the direction of maximum compressive stress (σ1), which may reflect geological differences between wells. We use the ratio of injection flow rate to overpressure, referred to as injectivity index, as a proxy for near-well permeability and compare changes in injectivity index to spatiotemporal characteristics of seismicity accompanying each test. Observed increases in injectivity index are generally poorly correlated with seismicity, suggesting that the locations of microearthquakes are not coincident with the zone of stimulation (i.e., increased permeability). Our findings augment a growing body of work suggesting that aseismic opening or slip, rather than seismic shear, is the active process driving well stimulation in many environments

Decompose and Conquer: Addressing Evasive Errors in Systems on Chip

Modern computer chips comprise many components, including microprocessor cores, memory modules, on-chip networks, and accelerators. Such system-on-chip (SoC) designs are deployed in a variety of computing devices: from internet-of-things, to smartphones, to personal computers, to data centers. In this dissertation, we discuss evasive errors in SoC designs and how these errors can be addressed efficiently. In particular, we focus on two types of errors: design bugs and permanent faults. Design bugs originate from the limited amount of time allowed for design verification and validation. Thus, they are often found in functional features that are rarely activated. Complete functional verification, which can eliminate design bugs, is extremely time-consuming, thus impractical in modern complex SoC designs. Permanent faults are caused by failures of fragile transistors in nano-scale semiconductor manufacturing processes. Indeed, weak transistors may wear out unexpectedly within the lifespan of the design. Hardware structures that reduce the occurrence of permanent faults incur significant silicon area or performance overheads, thus they are infeasible for most cost-sensitive SoC designs. To tackle and overcome these evasive errors efficiently, we propose to leverage the principle of decomposition to lower the complexity of the software analysis or the hardware structures involved. To this end, we present several decomposition techniques, specific to major SoC components. We first focus on microprocessor cores, by presenting a lightweight bug-masking analysis that decomposes a program into individual instructions to identify if a design bug would be masked by the program's execution. We then move to memory subsystems: there, we offer an efficient memory consistency testing framework to detect buggy memory-ordering behaviors, which decomposes the memory-ordering graph into small components based on incremental differences. We also propose a microarchitectural patching solution for memory subsystem bugs, which augments each core node with a small distributed programmable logic, instead of including a global patching module. In the context of on-chip networks, we propose two routing reconfiguration algorithms that bypass faulty network resources. The first computes short-term routes in a distributed fashion, localized to the fault region. The second decomposes application-aware routing computation into simple routing rules so to quickly find deadlock-free, application-optimized routes in a fault-ridden network. Finally, we consider general accelerator modules in SoC designs. When a system includes many accelerators, there are a variety of interactions among them that must be verified to catch buggy interactions. To this end, we decompose such inter-module communication into basic interaction elements, which can be reassembled into new, interesting tests. Overall, we show that the decomposition of complex software algorithms and hardware structures can significantly reduce overheads: up to three orders of magnitude in the bug-masking analysis and the application-aware routing, approximately 50 times in the routing reconfiguration latency, and 5 times on average in the memory-ordering graph checking. These overhead reductions come with losses in error coverage: 23% undetected bug-masking incidents, 39% non-patchable memory bugs, and occasionally we overlook rare patterns of multiple faults. In this dissertation, we discuss the ideas and their trade-offs, and present future research directions.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147637/1/doowon_1.pd

Slip on ridge transform faults : insights from earthquakes and laboratory experiments

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June, 2005The relatively simple tectonic environment of mid-ocean ridge transform fault (RTF) seismicity provides a unique opportunity for investigation of earthquake and faulting processes. We develop a scaling model that is complete in that all the seismic parameters are related to the RTF tectonic parameters. Laboratory work on the frictional stability of olivine aggregates shows that the depth extent of oceanic faulting is thermally controlled and limited by the 600°C isotherm. Slip on RTFs is primarily aseismic, only 15% of the tectonic offset is accommodated by earthquakes. Despite extensive fault areas, few large earthquakes occur on RTFs, and few aftershocks follow the large events. Standard models of seismicity, in which all earthquakes result from the same seismic triggering process, do not describe RTF earthquakes. Instead, large earthquakes appear to be preceded by an extended fault preparation process marked by abundant foreshocks within 1 hour and 15 km of the mainshocks. In our experiments normal force vibrations, such as seismic radiation from nearby earthquakes, can weaken and potentially destabilize steadily creeping faults. Integrating the rheology, geology, and seismicity of RTFs, we develop a synoptic model to better understand the spatial distribution of fault strength and stability and provide insight into slip accommodation on RTFs.Funding from the Deep Ocean Earth Institute Fellowship, MIT Presidential Fellowship, NSF Fellowship, and WHOI Academic Programs Office