Slow Slip Events And Small Earthquake Clustering
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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.
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).
Fault Mechanics And Transport Properties Of Rocks
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Author : Brian Evans
language : en
Publisher: Academic Press
Release Date : 1992-08-04
Fault Mechanics And Transport Properties Of Rocks written by Brian Evans and has been published by Academic Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992-08-04 with Science categories.
This festschrift, compiled from the symposium held in honor of W.F. Brace, is a timely overview of fault mechanics and transport properties of rock. State-of-the-art research is presented by internationally recognized experts, who highlight developments in this contemporary area of study subsequent to Bill Brace's pioneering work. Key Features * The strength of brittle rocks * The effects of stress and stress-induced damage on physical properties of rock * Permeability and fluid flow in rocks * The strength of rocks and tectonic processes
Implications And Limitations Of Tremor As A Proxy For Slow Slip
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Author : Kelley Hall
language : en
Publisher:
Release Date : 2020
Implications And Limitations Of Tremor As A Proxy For Slow Slip written by Kelley Hall and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.
This thesis seeks to integrate geodetic and seismic observations to explore the relationship between tremor and slow slip on subduction zones. In particular, I evaluate the one-to-one relationship of tremor and slip in space and time, and test various hypotheses that describe their interaction and scaling. This work adds insight into the state of the Cascadia subduction zone and the slow-slip seismic cycle. In the first chapter, I use the surface displacements measured by GPS stations to analyze six major episodic tremor and slip (ETS) events from 2007 to 2016 in northern Cascadia and invert for slip on a realistic plate interface. Tremor is typically constrained to a relatively narrow band along dip that is downdip of the inferred locked megathrust. My results indicate that slow slip extends updip of tremor by about 15 km beneath the Olympic Peninsula. Additionally, I find that along-strike variations in the amount of slow slip updip of tremor correspond to changes in lithology of the overlying crust. In these ETS events, slow slip extends from the downdip portion of the tremorgenic region beyond the updip extent of tremor, although still downdip of the inferred locked megathrust. Slip updip of tremor is a persistent feature of all six ETS events at this along-strike location. Inversions that restrict slip to occur only in regions that generated tremor produced slip distributions with unphysical characteristics and unsustainable concentrations at the updip part of the tremor footprint. Updip slow slip without tremor may suggest that the gap between stress and strength widens updip above the observed limit of tremor. In these ETS events, the regions updip of tremor may undergo ductile failure surrounding potentially tremorgenic patches. A widening gap between stress and strength in the updip direction is consistent with an observed along-dip dependence of LFE occurrence and numerical simulations of slow slip. Alternatively, rheological properties in the region updip of tremor may favor stable slip and not permit seismic slip (i.e. tremor). In the second chapter, I explore the evolution of slow slip on the Cascadia megathrust during two large ETS events and compare stress changes to the spatial evolution of tremor from PNSN tremor locations. I use displacement time series from GPS stations, along with the Extended Network Inversion Filter to solve for the time-dependent fault slip on the megathrust. The 2010 (Mw 6.8) and 2012 (Mw 6.8) slow slip events propagated northward and southward, respectively, allowing us to assess directional effects on slip behavior. I observe that tremor occurs on the leading edge of propagating slipping regions, well ahead of the highest slip rates, independent of the along-strike propagation direction. Using the tremor distribution to generate synthetic surface displacement data, resolution tests show that the result of peak tremor rates leading peak slip rates is not due to biases introduced by temporal smoothing. Calculated stress changes due to the time-dependent fault slip distributions imply that tremor is sensitive to kPa of stress, consistent with studies of tidally-triggered tremor. Within the resolution of our model, these results are consistent with the hypothesis that significant tremor is triggered by stresses ahead of the highest slip rates. I also observe ongoing slip continuing several days after tremor has passed. Our observations are consistent with some numerical models of tremor patches that suggest that this behavior can be explained by densely packed asperities, which act to widen the length scale of the slip pulse, rather than a narrow slip pulse. In the third chapter, I explore small slow slip events (SSEs), with Mw 6.0, and assesses whether fault slip and tremor detections scale linearly. Under the assumption that tremor and slip are spatially and temporally related during slow slip events, I develop a scaling relationship between tremor counts and slip based on known large slow slip events (SSEs) in Cascadia. I use the existing tremor catalog in Cascadia to cluster tremor detections into distinct events that can be scaled into slip distributions. Using this scaling relationship on a clustered tremor catalog, I obtain event magnitudes that range from Mw 4.5 to 6.5. We also find that the larger (Mo 3*1017 Nm) clustered events follow a Mo ~ T scaling. This catalog partially fills the long-standing observational gap between seismically detectable events and geodetically detectable events. GPS and strainmeters are used as an independent check of the scaling relationship. Using this clustered catalog as a guide, I identify a patch of repeating events beneath the Olympic Peninsula that produces frequent small SSEs. We stack the daily GPS time series for seven small slow slip events, aligning each record on peak tremor activity. We then estimate the average surface displacement and find the average moment. The GPS-based average moment for events in this patch is Mw 5.5 with peak fault slip reaching 0.6 cm and only 30% of the tremoring area slipping, compared to Mw 5.8 predicted by scaling the number of tremor detections. For further validation of our scaling relationship, I compare the scaled-tremor models to observed strainmeter records. We find that our empirical scaling relationship for large SSEs accurately predicts the strain for several small SSEs.
Aspects Of Earthquake Triggering And Seismicity Clustering
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Author : Xiaowei Chen
language : en
Publisher:
Release Date : 2013
Aspects Of Earthquake Triggering And Seismicity Clustering written by Xiaowei Chen 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.
Earthquakes strongly cluster in space and time, driven both by earthquake-to-earthquake triggering and underlying physical processes, such as tectonic stress loading, increased pore pressure, etc. I explore both global and regional datasets to understand characteristics of these processes in different tectonic environments. I study global seismicity using intermediate-period (35--70~s) Rayleigh waves recorded by the global seismic network. Applying a surface wave detect method identifies about 1000 previously un-cataloged earthquakes from 1997 to 2009, most of which are located in the southern ocean. I further analyze a small number of these events that are located in Antarctica to understand glacial-related triggering processes. Absolute and differential travel-times measured from waveform cross-correlation are used to obtain refined locations. A single-force model is applied to the observed amplitudes at 50~Hz to obtain best-fitting force directions. Additionally, possible glacial calving events are identified from MODIS images. The combined results suggest that events on Vanderford and Ninnis glaciers are a result of calving processes. To understand the general characteristics of earthquake clustering from a large dataset of earthquakes, I analyze seismicity in southern California. I use a high-resolution earthquake catalog based on waveform cross-correlation to study the spatial-temporal distribution of earthquakes. Parameters based on event location, magnitude and occurrence time are computed for isolated seismicity clusters. Spatial migration behavior is modeled using a weighted-least-squares method. Aftershock-like event clusters do not exhibit significant spatial migration compared with earthquake swarms. Two triggering processes are considered for swarms: slow slip and fluid diffusion, which are distinguished based on a statistical analysis of event migration. The results suggest fluid-induced seismicity is found across southern California, particularly within geothermal areas. In the Salton Sea geothermal field (SSGF), a correlation between seismicity and fluid injection activities is seen. Spatial-temporal variations of earthquake stress drops are investigated in different regions, and a distance-dependence of stress drop from the injection source is found in the SSGF, suggesting the influence of increased pore pressure. Temporal variation of stress drops within mainshock source regions shows that foreshocks and earthquake swarms have lower stress drops than background seismicity and aftershocks. These results, combined with the spatial migration observed for some large foreshock sequences, suggests an aseismic transient process is likely involved in foreshock triggering.
Characterization And Application Of Microearthquake Clusters To Problems Of Scaling Fault Zone Dynamics And Seismic Monitoring At Parkfield California
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Author : Robert Micheal Nadeau
language : en
Publisher:
Release Date : 1995
Characterization And Application Of Microearthquake Clusters To Problems Of Scaling Fault Zone Dynamics And Seismic Monitoring At Parkfield California written by Robert Micheal Nadeau and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1995 with categories.
Living On An Active Earth
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Author : National Research Council
language : en
Publisher: National Academies Press
Release Date : 2003-08-22
Living On An Active Earth written by National Research Council and has been published by National Academies Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2003-08-22 with Science categories.
The destructive force of earthquakes has stimulated human inquiry since ancient times, yet the scientific study of earthquakes is a surprisingly recent endeavor. Instrumental recordings of earthquakes were not made until the second half of the 19th century, and the primary mechanism for generating seismic waves was not identified until the beginning of the 20th century. From this recent start, a range of laboratory, field, and theoretical investigations have developed into a vigorous new discipline: the science of earthquakes. As a basic science, it provides a comprehensive understanding of earthquake behavior and related phenomena in the Earth and other terrestrial planets. As an applied science, it provides a knowledge base of great practical value for a global society whose infrastructure is built on the Earth's active crust. This book describes the growth and origins of earthquake science and identifies research and data collection efforts that will strengthen the scientific and social contributions of this exciting new discipline.
The Seismogenic Zone Of Subduction Thrust Faults
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Author : Timothy H. Dixon
language : en
Publisher: Columbia University Press
Release Date : 2007
The Seismogenic Zone Of Subduction Thrust Faults written by Timothy H. Dixon and has been published by Columbia University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with Computers categories.
Subduction zones, one of the three types of plate boundaries, return Earth's surface to its deep interior. Because subduction zones are gently inclined at shallow depths and depress Earth's temperature gradient, they have the largest seismogenic area of any plate boundary. Consequently, subduction zones generate Earth's largest earthquakes and most destructive tsunamis. As tragically demonstrated by the Sumatra earthquake and tsunami of December 2004, these events often impact densely populated coastal areas and cause large numbers of fatalities. While scientists have a general understanding of the seismogenic zone, many critical details remain obscure. This volume attempts to answer such fundamental concerns as why some interplate subduction earthquakes are relatively modest in rupture length (greater than 100 km) while others, such as the great (M greater than 9) 1960 Chile, 1964 Alaska, and 2004 Sumatra events, rupture along 1000 km or more. Contributors also address why certain subduction zones are fully locked, accumulating elastic strain at essentially the full plate convergence rate, while others appear to be only partially coupled or even freely slipping; whether these locking patterns persist through the seismic cycle; and what is the role of sediments and fluids on the incoming plate. Nineteen papers written by experts in a variety of fields review the most current lab, field, and theoretical research on the origins and mechanics of subduction zone earthquakes and suggest further areas of exploration. They consider the composition of incoming plates, laboratory studies concerning sediment evolution during subduction and fault frictional properties, seismic and geodetic studies, and regional scale deformation. The forces behind subduction zone earthquakes are of increasing environmental and societal importance.
The Gray Area
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Author : Alexandra Hutchison
language : en
Publisher:
Release Date : 2018
The Gray Area written by Alexandra Hutchison and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with Earth movements categories.
Slow earthquakes essentially represent a gray area of the slip spectrum, where regular fast slip earthquakes and aseismic creep constitute the spectrum's end members. Since their discovery in 2003 [Rogers and Dragert, 2003], increasing seismic observations, in addition to models, geodetic observations, and laboratory studies, have helped elucidate the nature of these events that vary quite vastly amongst themselves. Empirically, however, they share a linear moment rate scaling law that distinguishes them from regular earthquakes [Ide et al., 2007]. Slow earthquakes include, but are not limited to, low frequency earthquakes (LFEs), tremor, very low frequency earthquakes (VLFEs), slow slip events (SSEs), and episodic tremor and slip (ETS) events. Each type of these events has distinctive properties that makes their detection challenging. Furthermore, their relationships to each other remains unclear, particularly in terms of source properties. They may be important in the context of regular earthquakes and seismic hazard assessment as they appear to have a correlation with large events. Some slow earthquakes have been observed spatiotemporally preceding regular earthquakes such as the 2011 Mw 9.0 Tohoku earthquake [Kato et al., 2012] and the 2014 Mw 8.1 Iqueique earthquake [Ruiz et al., 2014]. Additionally, a region near the trench known to produce VLFEs ruptured coseismically during the Tohoku earthquake producing a larger earthquake and tsunami than was previously anticipated [Ide et al., 2012]. Ultimately, more observations and studies are required to understand the mechanical properties of slow earthquake source physics and to understand their greater role in the earthquake cycle.
Fundamentals Of Geophysics
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Author : William Lowrie
language : en
Publisher: Cambridge University Press
Release Date : 2020-01-02
Fundamentals Of Geophysics written by William Lowrie and has been published by Cambridge University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-01-02 with Science categories.
A thoroughly reworked third edition featuring new data acquisition technologies, research developments and computational exercises in Python.