Transient Viscosity and Afterslip of the 2015 Mw 8.3 Illapel, Chile, Earthquake

2019 ◽  
Vol 109 (6) ◽  
pp. 2567-2581 ◽  
Author(s):  
Rumeng Guo ◽  
Yong Zheng ◽  
Jianqiao Xu ◽  
Muhammad Shahid Riaz
Keyword(s):  
Stress Relaxation ◽  
Large Earthquake ◽  
Multilayered Structure ◽  
Rupture Zone ◽  
Postseismic Deformation ◽  
Viscoelastic Relaxation ◽  
Combined Model ◽  
Crust And Upper Mantle ◽  
Relaxation Effects ◽  
Viscoelastic Stress Relaxation

Abstract It is usually assumed that short‐term (a few years) postseismic deformation around the rupture zone is caused by continuing slip (afterslip) along the fault interface, and viscoelastic stress relaxation is only responsible for long‐term deformation. In order to verify the validity of this assumption, the initial 1.5 months postseismic displacements following the 2015 Mw 8.3 Illapel earthquake are analyzed based on a multilayered structure model. We explore the possible mechanisms, including afterslip and viscoelastic relaxation, which might have contributed to the postseismic deformation, and aim to distinguish the contributing ratio of different postseismic processes. The results show that either the models of kinematic afterslip or viscoelastic stress relaxation individually cannot match the observed horizontal and vertical postseismic displacements satisfactorily. However, a combined model considering both afterslip and viscoelastic relaxation effects can reduce the data misfit significantly and is more physically reasonable. In the preferred combined model, the transient viscosities of the lower crust and upper mantle are ∼6×1017  Pa s and ∼9×1017  Pa s, respectively. The difference between the afterslip distribution of the pure afterslip model and that of the combined model indicates that previous models based on pure elastic assumption have substantially underestimated the afterslip updip of the rupture zone, and overestimated the afterslip downdip of the rupture zone. Therefore, the role of viscoelastic stress relaxation is indispensable in the study of transient postseismic deformation following a large earthquake, which contradicts the conventional concept about deformation mechanisms of early postseismic process.

scholarly journals Stress relaxation arrested the mainshock rupture of the 2016 Central Tottori earthquake

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Yoshihisa Iio ◽  
Satoshi Matsumoto ◽  
Yusuke Yamashita ◽  
Shin’ichi Sakai ◽  
Kazuhide Tomisaka ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Focal Mechanism ◽  
Large Earthquake ◽  
Static Stress ◽  
Focal Mechanism Solutions ◽  
Large Earthquakes

AbstractAfter a large earthquake, many small earthquakes, called aftershocks, ensue. Additional large earthquakes typically do not occur, despite the fact that the large static stress near the edges of the fault is expected to trigger further large earthquakes at these locations. Here we analyse ~10,000 highly accurate focal mechanism solutions of aftershocks of the 2016 Mw 6.2 Central Tottori earthquake in Japan. We determine the location of the horizontal edges of the mainshock fault relative to the aftershock hypocentres, with an accuracy of approximately 200 m. We find that aftershocks rarely occur near the horizontal edges and extensions of the fault. We propose that the mainshock rupture was arrested within areas characterised by substantial stress relaxation prior to the main earthquake. This stress relaxation along fault edges could explain why mainshocks are rarely followed by further large earthquakes.

scholarly journals A Distinguishable Role of eDNA in the Viscoelastic Relaxation of Biofilms

mBio ◽  
2013 ◽  
Vol 4 (5) ◽  
Author(s):  
Brandon W. Peterson ◽  
Henny C. van der Mei ◽  
Jelmer Sjollema ◽  
Henk J. Busscher ◽  
Prashant K. Sharma
Keyword(s):  
Relaxation Time ◽  
Stress Relaxation ◽  
Time Constant ◽  
Extracellular Polymeric Substances ◽  
Principal Component ◽  
Mechanical Stresses ◽  
Extracellular Dna ◽  
Viscoelastic Relaxation ◽  
Content Type ◽  
Relaxation Time Constants

ABSTRACTBacteria in the biofilm mode of growth are protected against chemical and mechanical stresses. Biofilms are composed, for the most part, of extracellular polymeric substances (EPSs). The extracellular matrix is composed of different chemical constituents, such as proteins, polysaccharides, and extracellular DNA (eDNA). Here we aimed to identify the roles of different matrix constituents in the viscoelastic response of biofilms.Staphylococcus aureus,Staphylococcus epidermidis,Streptococcus mutans, andPseudomonas aeruginosabiofilms were grown under different conditions yielding distinct matrix chemistries. Next, biofilms were subjected to mechanical deformation and stress relaxation was monitored over time. A Maxwell model possessing an average of four elements for an individual biofilm was used to fit the data. Maxwell elements were defined by a relaxation time constant and their relative importance. Relaxation time constants varied widely over the 104 biofilms included and were divided into seven ranges (<1, 1 to 5, 5 to 10, 10 to 50, 50 to 100, 100 to 500, and >500 s). Principal-component analysis was carried out to eliminate related time constant ranges, yielding three principal components that could be related to the known matrix chemistries. The fastest relaxation component (<3 s) was due to the presence of water and soluble polysaccharides, combined with the absence of bacteria, i.e., the heaviest masses in a biofilm. An intermediate component (3 to 70 s) was related to other EPSs, while a distinguishable role was assigned to intact eDNA, which possesses a unique principal component with a time constant range (10 to 25 s) between those of EPS constituents. This implies that eDNA modulates its interaction with other matrix constituents to control its contribution to viscoelastic relaxation under mechanical stress.IMPORTANCEThe protection offered by biofilms to organisms that inhabit it against chemical and mechanical stresses is due in part to its matrix of extracellular polymeric substances (EPSs) in which biofilm organisms embed themselves. Mechanical stresses lead to deformation and possible detachment of biofilm organisms, and hence, rearrangement processes occur in a biofilm to relieve it from these stresses. Maxwell analysis of stress relaxation allows the determination of characteristic relaxation time constants, but the biofilm components and matrix constituents associated with different stress relaxation processes have never been identified. Here we grew biofilms with different matrix constituents and used principal-component analysis to reveal that the presence of water and soluble polysaccharides, together with the absence of bacteria, is associated with the fastest relaxation, while other EPSs control a second, slower relaxation. Extracellular DNA, as a matrix constituent, had a distinguishable role with its own unique principal component in stress relaxation with a time constant range between those of other EPSs.

Predicting variations of the least principal stress with depth: Application to unconventional oil and gas reservoirs using a log-based viscoelastic stress relaxation model

Geophysics ◽  
2022 ◽  
pp. 1-56
Author(s):  
Ankush Singh ◽  
Mark D. Zoback
Keyword(s):  
Stress Relaxation ◽  
Principal Stress ◽  
Oil And Gas ◽  
Learning Technologies ◽  
Stress Profile ◽  
Gas Reservoirs ◽  
Midland Basin ◽  
Multi Stage ◽  
Viscoelastic Stress Relaxation ◽  
Geophysical Logs

Knowledge of layer-to-layer variations of the least principal stress, S hmin, with depth is essential for optimization of multi-stage hydraulic fracturing in unconventional reservoirs. Utilizing a geomechanical model based on viscoelastic stress relaxation in relatively clay rich rocks, we present a new method for predicting continuous S hmin variations with depth. The method utilizes geophysical log data and S hmin measurements from routine diagnostic fracture injection tests (DFITs) at several depths for calibration. We consider a case study in the Wolfcamp formation in the Midland Basin, where both geophysical logs and values of S hmin from DFITs are available. We compute a continuous stress profile as a function of the well logs that fits all of the DFITs well. We utilized several machine learning technologies, such as bootstrap aggregation (or bagging), to improve the generalization of the model and demonstrate that the excellent fit between predicted and observed stress values is not the result of over-fitting the calibration points. The model is then validated by accurately predicting hold-out stress measurements from four wells within the study area and, without recalibration, accurately predicting stress as a function of depth in an offset pad about 6 miles away.

scholarly journals Illuminating subduction zone rheological properties in the wake of a giant earthquake

2019 ◽  
Vol 5 (12) ◽  
pp. eaax6720 ◽  
Author(s):  
Jonathan R. Weiss ◽  
Qiang Qiu ◽  
Sylvain Barbot ◽  
Tim J. Wright ◽  
James H. Foster ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Three Dimensional ◽  
Surface Strain ◽  
Postseismic Deformation ◽  
Crust And Upper Mantle ◽  
Plate Convergence ◽  
Maule Earthquake ◽  
History Of ◽  
Dependent Viscosity

Deformation associated with plate convergence at subduction zones is accommodated by a complex system involving fault slip and viscoelastic flow. These processes have proven difficult to disentangle. The 2010 Mw 8.8 Maule earthquake occurred close to the Chilean coast within a dense network of continuously recording Global Positioning System stations, which provide a comprehensive history of surface strain. We use these data to assemble a detailed picture of a structurally controlled megathrust fault frictional patchwork and the three-dimensional rheological and time-dependent viscosity structure of the lower crust and upper mantle, all of which control the relative importance of afterslip and viscoelastic relaxation during postseismic deformation. These results enhance our understanding of subduction dynamics including the interplay of localized and distributed deformation during the subduction zone earthquake cycle.

On the cause of enhanced landward motion of the overriding plate after a major subduction earthquake

2020 ◽  
Author(s):  
Mario D'Acquisto ◽  
Matthew Herman ◽  
Rob Govers
Keyword(s):  
Subduction Zones ◽  
Relaxation Times ◽  
Underlying Mechanism ◽  
Rupture Zone ◽  
Elastic Response ◽  
Postseismic Deformation ◽  
Plate Interface ◽  
Mechanical Coupling ◽  
Megathrust Earthquakes ◽  
Viscous Relaxation

&lt;div&gt; &lt;p&gt;During and after a large megathrust earthquake, the overriding plate above the rupture zone moves oceanward. Enigmatically, the post-seismic motion of the overriding plate after several recent large earthquakes, further along strike from the rupture zone, was faster in the landward direction than before the event. Previous studies interpreted these changes as the result of increased mechanical coupling along the megathrust interface, transient slab acceleration, or bulk postseismic deformation with elastic bending mentioned as a possible underlying mechanism. Before invoking additional mechanisms, it is important to understand the contribution of postseismic deformation processes that are inherent features of megathrust earthquakes. We thus aim to quantify and analyse the deformation that produces landward motion during afterslip and viscous relaxation.&amp;#160;&lt;/p&gt; &lt;/div&gt;&lt;div&gt; &lt;p&gt;We use velocity-driven 3D mechanical finite element models, in which large megathrust earthquakes occur periodically on the finite plate interface. The model geometry is similar to most present-day subduction zones, but does not exactly match any specific subduction zone.&amp;#160;&lt;/p&gt; &lt;/div&gt;&lt;div&gt; &lt;p&gt;The results show increased post-seismic landward motion at (trench-parallel) distances greater than 450 km from the middle of the ruptured asperity. Similar patterns of landward motion are generated by viscous relaxation in the mantle wedge and by deep afterslip on the shear zone downdip of the brittle megathrust interface. Landward displacement due to postseismic relaxation largely accumulates at exponentially decaying rates until ~6 Maxwell relaxation times after the earthquake. The spatial distribution and magnitude of the velocity changes is broadly consistent with observations related to both the 2010 Maule and the 2011 Tohoku-oki earthquakes.&amp;#160;&amp;#160;&lt;/p&gt; &lt;/div&gt;&lt;div&gt; &lt;p&gt;Further model experiments show that patterns of landward motion due to afterslip and to viscous relaxation are insensitive to the locking pattern of the megathrust. However, the locking distribution does affect the magnitudes of the displacements and velocities. Results show that the increased landward displacement due to postseismic deformation scales directly proportionally to seismic moment.&amp;#160;&lt;/p&gt; &lt;/div&gt;&lt;div&gt; &lt;p&gt;We conclude that the landward motion results from in-plane horizontal bending of the overriding plate and mantle. This bending is an elastic response to oceanward tractions near the base of the plate around the ruptured asperity, causing extension locally and compression further away along-trench. This elastic in-plate bending consistently contributes to earthquake-associated changes in surface velocities for the biggest megathrust earthquakes, producing landward motion along strike from the rupture zone.&lt;/p&gt; &lt;/div&gt;

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