Slow Earthquakes
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Slow Earthquakes
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Author : Ariane Ducellier
language : en
Publisher:
Release Date : 2022
Slow Earthquakes written by Ariane Ducellier and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with categories.
The focus of this thesis is slow earthquakes, that is earthquake-like events that release energy over a period of hours to months, rather than the seconds to minutes characteristic of a typical earthquake. Slow slip events were discovered in many subduction zones during the last two decades thanks to recordings of the displacement of Earth's surface by Global Navigation Satellite Systems (GNSS) networks. As ordinary earthquakes, slow slip events are caused by slip on a fault (for instance, the plate boundary between a tectonic plate subducting under another tectonic plate). However, they take a much longer time (several days to several years) to happen relative to ordinary earthquakes, they have a relatively short recurrence time (months to years), compared to the recurrence time of regular earthquakes (up to several hundreds of years), and the seismic waves they generate are much weaker than the seismic waves generated by ordinary earthquakes and may not be detectable. A slow slip event is inferred to happen when there is a reversal of the direction of motion at GNSS stations, compared to the inter-seismic motion of the surface displacement. In many places, tectonic tremor is also observed in relation to slow slip. Tremor is a long (several seconds to many minutes), low amplitude seismic signal, with emergent onsets, and an absence of clear impulsive phases. Tectonic tremor has been explained as a swarm of small, low-frequency earthquakes (LFEs), that is small magnitude earthquakes (M ~ 1) with frequency content (1-10 Hz) lower than for ordinary earthquakes (up to 20 Hz). Low-frequency earthquakes are usually grouped into families of events, with all the earthquakes of a given family originating from the same small patch on the plate interface and recurring more or less episodically in a bursty manner. Due to the lack of clear impulsive phases in the tremor signal, it is difficult to determine the depth of the tremor source and the distance of the source to the plate interface with great precision. The thickness of the tremor region is also not well constrained. The tremor may be located on a narrow fault as the low-frequency earthquakes appear to be or distributed over a few kilometers wide low shear-wave velocity layer in the upper oceanic crust, which is thought to be a region with high pore-fluid pressure. In the second chapter of this thesis, I compute lag times of peaks in the cross-correlation of the horizontal and vertical components of tremor seismograms, recorded by small-aperture arrays in the Olympic Peninsula, Washington, and interpret them to to be S minus P times. I estimate tremor depths from these S minus P times using epicenters from a previous study using a multibeam back-projection method. The tremor is located close to the plate boundary in a region no more than 2-3 kilometers thick and is very close to the depths of low-frequency earthquakes. The tremor is distributed over a wider depth range than the low-frequency earthquakes. However, due to the uncertainty on the depth, it is difficult to conclude whether the source of the tremor is located at the top of the subducting oceanic crust, in the lower continental crust just above the plate boundary, or in a narrow zone at the plate boundary. In the third chapter of this thesis, I extend the LFE catalog obtained by Plourde et al. (2015) during an episode of high tremor activity in April 2008, to the 8-year-long period 2004-2011. All of the tremor in the Boyarko et al. (2015) catalog south of 42 degrees North has associated LFE activity, but I have identified several other, mostly smaller, clusters of LFEs, and extend their catalog forward and backward by a total of about 3 years. As in northern Cascadia, the down-dip LFE families have recurrence intervals several times smaller than the up-dip families. For the April 2008 Episodic Tremor and Slip event, the best recorded LFE families exhibit a strong tidal Coulomb stress sensitivity starting 1.5 days after the rupture front passes by each LFE family. This behavior is very similar to what has been observed in northern Cascadia, even though the predicted Coulomb stress is about half the magnitude in the south. The southernmost LFE family, which has been interpreted to be on the subduction plate boundary, near the up-dip limit of tremor, has a very short recurrence time. Also, these LFEs tend to occur during times when predicted tidal Coulomb stress is discouraging slip on the plate boundary. Both observations suggest this LFE family may be on a different fault, perhaps a crustal fault. In many places, tectonic tremor is observed in relation to slow slip and can be used as a proxy to study slow slip events of moderate magnitude where surface deformation is hidden in GNSS noise. However, in places where no clear relationship between tremor and slow slip occurrence is observed, these methods cannot be applied, and we need other methods to be able to better detect and quantify slow slip. In the fourth chapter of this thesis, I use the Maximal Overlap Discrete Wavelet Transform (MODWT) to analyze GNSS time series and seismic recordings of slow slip events in Cascadia. I use detrended GNSS data, apply the MODWT transform and stack the wavelet details from several neighboring GNSS stations. As an independent check on the timing of slow slip events, I also compute the cumulative number of tremors in the vicinity of the GNSS stations, detrend this signal, and apply the MODWT transform. I then assume that there is a transient, interpreted as a slow slip event, whenever there is a positive peak followed by a negative peak in the wavelet signal. I verify that there is a good agreement between slow slip events detected with only GNSS data, and slow slip events detected with only tremor data. The wavelet-based detection method detects well events of magnitude higher than 6 as determined by independent event catalogs (Michel et al., 2019).
The Transition From Stable To Slow To Fast Earthquake Slip On Faults
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Author : Agathe M. Eijsink
language : en
Publisher:
Release Date : 2021
The Transition From Stable To Slow To Fast Earthquake Slip On Faults written by Agathe M. Eijsink and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with categories.
Over the last decades, new types of earthquakes have been discovered. The most well-known group of ordinary earthquakes might be the most dangerous as they emit the largest amount of seismic radiation and cause ground-shaking, but repeating slow earthquakes can also damage buildings and infrastructure. Ordinary earthquakes occur when movement on a fault is unstable and a run-away process accelerates the movement to seismogenic velocities. During slow earthquakes, there are also clearly defined phases of faster slip along the fault, but the maximum slip velocity reached during these phases is lower. Then, there are aseismic faults, where slip accumulates constantly by stable creep at a rate close to the far-field stressing rate. The mechanisms that control the nature of sliding behavior of faults are multiple and studied in more or less detail. In this thesis, I explore how three factors influence fault stability: fault surface roughness and roughness anisotropy, fault-normal stiffness and stiffness contrasts across a fault, and the lithological controls on the extraordinary shallow slow slip events in the Hikurangi subduction zone margin (New-Zealand). Here, I present results using direct shear experiments, while varying one of the studied variables. To study the influence of fault surface morphology, I use two materials; a velocity-weakening and therefore potentially unstable pure quartz powder, and Rochester shale powder, which is velocity-strengthening and therefore likely to show stable sliding. Fault surface morphology evolves with displacement and its influence on frictional behavior is therefore studied by varying the amount of displacement on the samples. To test the influence of host-rock stiffness, the testing device is fitted with springs of variable stiffness in both the shear-parallel and fault-normal directions. Testing occurs on the intrinsically unstable quartz powder and I analyze both the frictional properties as well as the slip instabilities that occur. For the study about the Hikurangi margin, I use samples of the sediments on the incoming plate and use realistically low deformation rates, to study the frictional behavior and the occurrence of spontaneous slow slip events during the experiments. The results show rough, isotropic faults can host slip instabilities, because these show the required velocity-weakening frictional behavior. Striated, smooth surfaces are velocity-strengthening and promote stable sliding. The formed fault surfaces obey the typical self-affine fractal scaling, that make these results directly applicable to natural faults. Reducing the fault-normal stiffness causes the fault to become less velocity-weakening and would therefore promote stable sliding. However, slip instabilities occur when the fault-normal stiffness is reduced, which I explain by a different mechanism that requires a stiffness asymmetry. The asymmetry is the result of reducing the fault-normal stiffness on one side of the fault. The plate-rate shear experiments on Hikurangi sediments show spontaneous slow slip events occur in the calcite-rich lithologies, whereas the weakest lithologies are velocity-strengthening. Altogether, the results presented in this thesis suggest unstable sliding will occur on rough, isotropic fault patches. The slow slip events in the Hikurangi margin can only occur when the slow slip event-hosting lithologies are introduced into the deformation zone. This could be explained by a geometrically complex deformation zone due to subducting seamounts. Stiffness contrasts, due to lithological contrast across a fault or due to asymmetric damage, may cause slip instabilities that are not explained by the traditional critical stiffness theory. I show the three studied variables are closely linked and fault surface roughness, fault stiffness and stiffness contrast, as well as fault zone lithology may affect each other.
The Physics Of Slow Slip Tremor And Associated Seismicity From Geodetic And Laboratory Studies
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Author : Noel McCay Bartlow
language : en
Publisher:
Release Date : 2013
The Physics Of Slow Slip Tremor And Associated Seismicity From Geodetic And Laboratory Studies written by Noel McCay Bartlow and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
Slow slip events, sometimes also called slow earthquakes, have been the subject of intense study since they were discovered in the late 1990's. Slow slip events (SSEs) occur when a fault within the earth slips, as in an earthquake, but more slowly than in an earthquake. SSEs take anywhere from days to years to release the same energy as a Mw 5 - 7.5 earthquake would release in seconds. Because of their slow nature, SSEs do not excite seismic waves in the earth like regular earthquakes do, and thus do not cause the dangerous ground shaking or other hazards (i.e. liquifaction, tsunamis) associated with earthquakes. However SSEs still perturb the static stress state within the earth in the same way that earthquakes do, and can trigger regular earthquakes which may be damaging. SSEs are found in areas that are transitional between largely locked fault regions and freely creeping regions. Typically these SSE regions occur on the deeper extent of faults, below the depth of most earthquakes, however some SSEs occur on shallow transitional regions shallower than most earthquakes. SSEs present a unique window into the physics of these transitional fault regions, and thus present an opportunity to re ne our understanding of fault mechanics. SSEs are sometimes accompanied by an emergent seismic signal called tectonic tremor. Tectonic tremor is thought to be composed of individual very small, lowfrequency earthquakes which represent faster slip on small patches either within or adjacent to the active SSE region. The precise relationship between slip and tremor is not well understood, but has implications for the physics of deep fault regions, the hazards associated with SSE triggered earthquakes, and monitoring of SSEs. Tectonic tremor is studied by multiple researchers from a seismological point of view, using seismic instruments. When present, the total energy released in as tectonic tremor is always orders of magnitude below the total energy released by slip as measured by geodetic instruments, indicating that most of the slip is occurring aseismically. Additionally, some SSEs have no tremor associated with them. Therefore, SSEs are most suited to study using geodesy, as well as laboratory and modeling studies. In this thesis, I present a number of studies of GPS data from SSEs in the Cascadia subduction zone in the United States, the Hikurangi subduction zone on North Island of New Zealand, and the Boso peninsula area of Japan. I use a time-depenent inversion method to study the time-dependent properties of the SSEs, such as acceleration and migration of slip. I then use these models to study in detail the relationships between SSEs, seismicity, and tremor in these regions. I also present one laboratory study in which I create stress conditions similar to those thought to exist in SSE regions in subduction zones, including pressurized pore fluid. I extrapolate the results of this study to explain why SSE associated tremor is often modulated by solid earth tides, while regular earthquakes are not.
Physics Of Megathrust Earthquakes
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Author : Sylvain Barbot
language : en
Publisher: Birkhäuser
Release Date : 2020-04-24
Physics Of Megathrust Earthquakes written by Sylvain Barbot and has been published by Birkhäuser this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-04-24 with Science categories.
This topical volume on the physics of megathrust earthquakes investigates many aspects of the earthquake phenomenon, from the geodynamic setting of subduction zones, to interseismic and postseismic deformation, slow-slip events, dynamic rupture, and tsunami generation. The dynamics of the seismic cycle at megathrusts is rich in various types of earthquakes, many of which only recently discovered. Our early understanding of the earthquake phenomenon was a type of stick-slip motion, where the fault is loaded by tectonic forces for an extended period, followed by rapid failure. Extensive seismic and geodetic monitoring of subduction zones has revealed a much more varied seismic behavior, where episodic fault slip can occur at any slip velocity between the background loading rate, of the order of a few atoms per second, and the fast seismic range, about a meter per second. Events that fill the gap between slow creep and fast ruptures include a host of slow earthquakes. Subduction zones therefore provide a natural laboratory to better understand the physics of earthquakes and faulting. Previously published in Pure and Applied Geophysics, Volume 176, Issue 9, 2019 The chapters “Interseismic Coupling and Slow Slip Events on the Cascadia Megathrust”, “Effect of Slip-Weakening Distance on Seismic–Aseismic Slip Patterns”, “Physics-Based Scenario of Earthquake Cycles on the Ventura Thrust System, California: The Effect of Variable Friction and Fault Geometry”, and “A Secondary Zone of Uplift Due to Megathrust Earthquakes” are available as open access articles under a CC BY 4.0 license at link.springer.com
Hydrological Geochemical And Geophysical Changes Related To Earthquakes And Slow Slip Events
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Author : Chi-Yu King
language : en
Publisher: Birkhäuser
Release Date : 2018-11-12
Hydrological Geochemical And Geophysical Changes Related To Earthquakes And Slow Slip Events written by Chi-Yu King and has been published by Birkhäuser this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-11-12 with Science categories.
It has been documented for many centuries that earthquakes and other tectonic processes have hydrological effects. The magnitude and the spatial and temporal patterns of such signals recorded by scientific instruments in modern times have not always been straightforward to explain, and hence remain the subject of active research, especially those that might be precursors to earthquakes. This volume contains 9 papers that present new observations on earthquake-related hydrological, geochemical, and geophysical changes in Japan, Taiwan, Baja California in Mexico, and mostly China, one paper on laboratory rock-mechanics study, and a brief overview of Chinese research on earthquake prediction during the past 5 decades. Some of the observed changes occurred several days before earthquakes, and are explained with the consideration of heterogeneity of the earth's crust and earthquake-related slow-slip events, with earthquake forecasting as a possible application.
Mechanics Of Earthquake Faulting
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Author : A. Bizzarri
language : en
Publisher: IOS Press
Release Date : 2019-07-19
Mechanics Of Earthquake Faulting written by A. Bizzarri and has been published by IOS Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019-07-19 with Science categories.
The mechanics of earthquake faulting is a multi-disciplinary scientific approach combining laboratory inferences and mathematical models with the analysis of recorded data from earthquakes, and is essential to the understanding of these potentially destructive events. The modern field of study can be said to have begun with the seminal papers by B. V. Kostrov in 1964 and 1966. This book presents lectures delivered at the summer school ‘The Mechanics of Earthquake Faulting’, held under the umbrella of the Enrico Fermi International School of Physics in Varenna, Italy, from 2 to 7 July 2018. The school was attended by speakers and participants from many countries. One of the most important goals of the school was to present the state-of-the-art of the physics of earthquakes, and the 10 lectures included here cover the most challenging aspects of the mechanics of faulting. The topics covered during the school give a very clear picture of the current state of the art of the physics of earthquake ruptures and also highlight the open issues and questions that are still under debate, and the book will be of interest to all those working in the field.
Slow Slip Events And Small Earthquake Clustering
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Author : R. J. Beavan
language : en
Publisher:
Release Date : 2008
Slow Slip Events And Small Earthquake Clustering written by R. J. Beavan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with Earth movements categories.
Earthquakes
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Author :
language : en
Publisher: BoD – Books on Demand
Release Date : 2019-09-11
Earthquakes written by and has been published by BoD – Books on Demand this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019-09-11 with Technology & Engineering categories.
This book is a collection of scientific papers on earthquake preparedness, vulnerability, resilience, and risk assessment. Using case studies from various countries, chapters cover topics ranging from early warning systems and risk perception to long-term effects of earthquakes on vulnerable communities and the science of seismology, among others. This volume is a valuable resource for researchers, students, non-governmental organizations, and key decision-makers involved in earthquake disaster management systems at national, regional, and local levels.
Study On Generation Mechanism Of Slow Earthquakes
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Author :
language : en
Publisher:
Release Date : 2019
Study On Generation Mechanism Of Slow Earthquakes written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with categories.
Laboratory Studies Of Fault Stability And Slow Earthquakes
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Author : John Leeman
language : en
Publisher:
Release Date : 2017
Laboratory Studies Of Fault Stability And Slow Earthquakes written by John Leeman and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.
Fault zones are areas of localized deformation that accommodate strain in the Earth's crust accumulated over time due to tectonic motion or stress transfer from adjacent areas. Faults are traditionally considered to accommodate this strain by either constant slow movement (creep), or by rapid catastrophic failure events (earthquakes). The behavior of faults which produce earthquakes has been extensively studied, including characterization of the time and slip predictability of earthquakes, frequency-magnitude distributions, aftershock decay patterns, dynamic triggering, and frictional processes. Chance observations in global positioning system (GPS) data from the Vancouver Island area in 2001 revealed a new kind of fault slip that had not been considered before, slow-slip events. Since those early observations, slow-slip events have been observed at most major subduction interfaces and even in glacial systems. In this dissertation, I strive to answer some of the fundamental questions about slow-slip systems. Little is known about the dynamics of these systems and how they operate. Scattered laboratory observations have provided clues, but this study is the first systematic examination of slow-slip earthquakes and their frictional behavior in the laboratory. I examine questions such as what controls how a fault zone will fail and what the velocity and normal stress sensitives are, then connect those mechanisms to observations from a natural slow-slip system beneath Whillans Ice Stream in western Antarctica.In chapter 1, I demonstrate how to modify the stiffness of the testing machine to create slow-slip events in the laboratory in an artificial granular material. I also present a method to automatically calculate the stiffness of each slip event in a given experiment. Chapter 2 extends this work into a synthetic fault gouge material and carefully examines the sensitivity of the system to the stiffness of the testing apparatus. Chapter 3 introduces the new parameter of velocity dependence into the test suite and demonstrates that designer frictional laws (those whose velocity dependence of friction is itself velocity dependent) are not necessary to explain observations of slow-slip. Chapter 4 introduces the field area of Whillans Ice Stream, a system that hosts slow-slip events daily at an ice-till interface approximately 1 km below the ice surface. I test samples of the till obtained by piston coring of the ice stream in 1989 and develop a simple hydrologic model to determine the potential stress states of the system and an effective medium model to predict the acoustic velocities under those stresses. The entire system is then examined in the light of stability theory to postulate why it has been able to remain in the slow-slip regime for as long as it has been observed. Finally, in chapter 5 I examine the generation of electrical potential differences on slipping experimental faults and critically evaluate the generation mechanisms proposed in the literature.This dissertation provides insight into the mechanisms and controls of fault slip. I demonstrate that fault failure is not a bifurcation between stable and unstable, but rather a continuous spectrum of failure modes from slow to fast stick-slip. The evidence provided shows that the stiffness of the system is the dominant controlling mechanism and that higher order frictional terms are not required to explain the basic spectrum of behaviors observed.