Slip Area Research Articles

Configuration and structure of the Philippine Sea Plate off Boso, Japan: constraints on the shallow subduction kinematics, seismicity, and slow slip events

We applied tomographic inversion and receiver function analysis to seismic data from ocean-bottom seismometers and land-based stations to understand the structure and its relationship with slow slip events off Boso, Japan. First, we delineated the upper boundary of the Philippine Sea Plate based on both the velocity structure and the locations of the low-angle thrust-faulting earthquakes. The upper boundary of the Philippine Sea Plate is distorted upward by a few kilometers between 140.5 and 141.0°E. We also determined the eastern edge of the Philippine Sea Plate based on the delineated upper boundary and the results of the receiver function analysis. The eastern edge has a northwest–southeast trend between the triple junction and 141.6°E, which changes to a north–south trend north of 34.7°N. The change in the subduction direction at 1–3 Ma might have resulted in the inflection of the eastern edge of the subducted Philippine Sea Plate. Second, we compared the subduction zone structure and hypocenter locations and the area of the Boso slow slip events. Most of the low-angle thrust-faulting earthquakes identified in this study occurred outside the areas of recurrent Boso slow slip events, which indicates that the slow slip area and regular low-angle thrust earthquakes are spatially separated in the offshore area. In addition, the slow slip areas are located only at the contact zone between the crustal parts of the North American Plate and the subducting Philippine Sea Plate. The localization of the slow slip events in the crust–crust contact zone off Boso is examined for the first time in this study. Finally, we detected a relatively low-velocity region in the mantle of the Philippine Sea Plate. The low-velocity mantle can be interpreted as serpentinized peridotite, which is also found in the Philippine Sea Plate prior to subduction. The serpentinized peridotite zone remains after the subduction of the Philippine Sea Plate and is likely distributed over a wide area along the subducted slab.

Land Surface Temperature Variation Following the 2017 Mw 7.3 Iran Earthquake

During an earthquake, crustal deformation, fluid flow, and temperature variation are coupled; however, earthquake-related land surface temperature (LST) variations remain unclear. To determine whether post-seismic fluid migration can cause changes in LST, and taking the Mw 7.3 2017 Iran earthquake as an example, we modeled surface cooling (CA) and warming (WA) areas induced by co-seismic slip and fluid migration using a thermo-hydro-mechanical (THM) coupled numerical simulation. Moreover, using nighttime LST data with 15-min resolution, the daily attenuation coefficient k of nighttime LST was extracted by attenuation function fitting, and the trend of the k time series was analyzed using the Mann–Kendall and Sen’s methods. Based on the comparison of k trends between the post-seismic and 2010–2016 periods, we obtained cooling and warming trends for the modeled CA and WA. The numerical simulation and observational data show good consistency, and both indicate that fluid migration caused by crustal deformation can lead to changes in LST. The numerical simulations show that after the Iran earthquake, the surface projection area of co-seismic slip correlated with a cooling area (CA), while the surrounding area correlated with a warming area (WA). For the LST observational data, the post-seismic k trends of the calculated CA and WA are positive and negative, indicating sustained cooling and warming processes, respectively. This study provides evidence that LST variation is caused by co-seismic crustal deformation and fluid migration and reveals the coupled evolution of deformation, fluid, and temperature fields. The results provide new insights into the mechanisms of seismic thermal anomalies.

2D spatial distribution of reflection intensity on the upper surface of the Philippine Sea plate off the Boso Peninsula, Japan

The region off the Boso Peninsula, Japan, is a tectonically complex area where the Pacific plate is subducting beneath both the landward plate and the Philippine Sea plate (PHS) from the Japan trench and the Izu-Bonin trench as the PHS is subducting under the landward plate from the Sagami trough. It is important to better determine the structure of this region to deepen our understanding of its seismicity. Previous seismic reflection studies have shown that reflections from the upper surface of the PHS vary with depth, being stronger in the main slip area of the slow slip events beneath the Boso Peninsula (Boso SSEs). However, the spatial relationship between the reflective area and the SSEs is poorly constrained. This study mapped the distribution of the reflective area using data recorded by ocean bottom seismometers during an active-source seismic experiment. We constructed a 3D P-wave velocity structure by using traveltimes of first arrivals from 18 ocean bottom seismometer records. We also adapted the traveltime mapping method to reflection traveltimes, projecting them to the depth–distance domain, to map the 2D distribution of strong reflections from the top of the PHS. These reflections were concentrated in two areas, one near the main slip area of the Boso SSEs and the other about 60km to the east. In the first area, the absence of strong velocity contrasts near the top of the PHS suggests that the reflections were generated by a thin low-velocity layer. In contrast, the structure of the second area has a convex shape of high velocity with a high velocity gradient near the top of the PHS. This structure may represent boninitic material of the outer-arc high, partially serpentinized peridotite, or gabbro displaced by intraoceanic reverse faults.

Estimation of Strong Motion Generation Area for the 2004 Parkfield Earthquake Using Empirical Green’s Function Method

The empirical Green’s function (EGF) method is used to simulate the 2004 Parkfield earthquake (Mw = 6.1). The strong motion generation areas (SMGA) are estimated to reproduce near-source ground motions in a broadband frequency range of 0.25–10 Hz. In this simulation, the EGF uses the small events that occurred in 2005 (Mw = 4.5), 2012 (Mw = 4.4), 2010 (Mw = 4), and 2007 (Mw = 4). The source spectral ratio estimates the seismic moment ratio between large and small events whose corner frequencies obey the omega-squared scaling law. The estimated SMGA is 12 km in length by 8 km in width and is located near the large slip area of the waveform inversion. The result shows that the rupture propagates radially from the southeastern bottom part of the SMGA toward the northwestern shallow direction. In addition, a characterized source model comprising two asperities and a background slip area is proposed. The rupture propagates from asperity1 toward asperity2 with 2 s time delay. The characterized source model simulates more accurately than the single SMGA. The comparison between the 5% damped pseudo acceleration response spectra of our simulations verifies a better compatibility for more than 2 Hz.

Source rupture process of the 2018 Hokkaido Eastern Iburi earthquake deduced from strong-motion data considering seismic wave propagation in three-dimensional velocity structure

The source rupture process of the 2018 Hokkaido Eastern Iburi earthquake (MJMA 6.7) was analyzed by a kinematic waveform inversion method using strong-motion data in 0.04–0.5 Hz. This earthquake occurred close to the Hidaka Collision Zone and the Ishikari depression, where the crustal structure is rather complex. Thus, we used a three-dimensional velocity structure model to compute the theoretical Green’s functions by the finite difference method. A source fault model with strike-angle variation was set based on the spatial distribution of the early aftershocks. The strong-motion stations used for the source inversion were selected based on the result of forward ground motion simulation of a moderate aftershock. The slip in the first 5 s was relatively small, but an area of significant slip with peak slip of 1.7 m was found in the depth range from 22 to 32 km. The rupture propagated upward mainly in the southwest direction. Based on the regional crustal structure and the configuration of the Moho discontinuity, the large-slip area was thought to be located in the lower crust, and its rupture did not reach the upper part of the continental crust. Most of the early aftershocks occurred around the large-slip area. The later aftershocks at the depth shallower than 20 km occurred outside the causative source fault of the mainshock. Three-dimensional ground motion simulation demonstrated that the heterogeneous source process and the three-dimensional basin and crustal velocity structure brought a large velocity pulse to an area to the southwest of the source fault, where the largest PGV was observed during the mainshock. The spatial distribution of the simulated PGV resembled the observed PGV distribution except some sites located inside the Ishikari depression where thick Quaternary soft low-velocity sediments exist at the top of the basin.

Source Characteristics of the 28 September 2018 Mw 7.4 Palu, Indonesia, Earthquake Derived from the Advanced Land Observation Satellite 2 Data

On 28 September 2018, an Mw 7.4 earthquake, followed by a tsunami, struck central Sulawesi, Indonesia. It resulted in serious damage to central Sulawesi, especially in the Palu area. Two descending paths of the Advanced Land Observation Satellite 2 (ALOS-2) synthetic aperture radar (SAR) data were processed with interferometric synthetic aperture radar (InSAR) and pixel tracking techniques to image the coseismic deformation produced by the earthquake. The deformation measurement was used to determine the fault geometry and the coseismic distributed slip model with a constrained least square algorithm based on the homogeneous elastic half-space model. We divided the fault into four segments (named AS, BS, CS and DS, from the north to the south) in the inversion. The BS segment was almost parallel to the DS segment, the CS segment linked the BS and DS segments, and these three fault segments formed a fault step-over system. The Coulomb failure stress (CFS) change on the causative fault was also calculated. Results show that the maximum SAR line-of-sight (LOS) and horizontal deformation were −1.8 m and 3.6 m, respectively. The earthquake ruptured a 210-km-long fault with variable strike angles. The ruptured pattern of the causative fault is mainly a sinistral slip. Almost-pure normal characteristics could be identified along the fault segment across the Palu bay, which could be one of the factors resulting in the tsunami. The main slip area was concentrated at the depths of 0–20 km, and the maximum slip was 3.9 m. The estimated geodetic moment of the earthquake was 1.4 × 1020 Nm, equivalent to an earthquake of Mw 7.4. The CFS results demonstrate that the fault step-over of 5.3 km width did not terminate the rupture propagation of the main shock to the south. Two M>6 earthquakes (the 23 January 2005 and the 18 August 2012) decreased CFS along CS segment and the middle part of DS segment of the 2018 main shock. This implies that the stress release during the previous two earthquakes may have played a vital role in controlling the coseismic slip pattern of the 2018 earthquake.

The role of slow screw dislocations in controlling fast strain avalanche dynamics in body-centered cubic metals

Plasticity in body centered cubic (BCC) crystals is shown to be controlled by slow screw dislocation motion, owing to the thermally-activated process of kink pair nucleation and migration. Through three dimensional discrete dislocation dynamics simulations, this work unravels the mystery of how such slow screw dislocation behavior contributes to extremely rapid strain bursts in submicron BCC tungsten (W) pillars, which is typical of BCC metals. It is found that strain bursts are dominated by the motion of non-screw dislocations at low strain rate, but are more influenced by screw dislocations at high strain rate. The total, and partial strain burst magnitude due to screw dislocations alone, are found to exhibit rate dependence following a power law statistics with exponent of 0.65. Similar power law statistics are also obeyed for the standard deviation of the corresponding plastic strain rate. The role of screw dislocations is attributed to the changing nature of dislocation source operation at different strain rates. The corresponding spatial distribution of plastic deformation is also discussed based on the uniqueness of the simulation method in reproducing the distribution of slipped area and plastic strain with very high spatial resolution.

Influence of tectonic stress regime on the magnitude distribution of induced seismicity events related to hydraulic fracturing

Hydraulic fracturing is today the primary means of initiating, increasing, and maintaining well productivity in unconventional shale gas reservoirs. However, hydraulic fracturing is attracting public concern over its rapid growth in use and environmental footprint, including potential hazards such as induced seismicity. To mitigate these concerns, there is a need to better understand the level of hazard present with respect to the magnitudes of the events possible, recognizing that these are not equal across different shale gas plays due to regional differences in the geological conditions or even within the same shale gas play due to local differences.An empirical study is presented here along with a series of numerical simulations to investigate the influence of the tectonic stress regime on the magnitude and magnitude distribution of induced seismicity events related to hydraulic fracturing practices. A database of determined earthquake focal mechanisms was first used to determine the tectonic stress regime for different North American shale gas basins. Next, induced events associated with hydraulic fracturing operations were identified to determine the magnitude distributions and b-values for these different shale gas basins. To support these empirical analyses, 3-D numerical modelling was performed to further investigate the mechanistic responses and event magnitudes under different simulated stress regimes. The empirical analysis results show that thrust faulting stress regimes have lower b-values than strike-slip stress regimes and therefore are more susceptible to larger induced seismicity events. The numerical simulations show that this is related to the stresses acting on a thrust fault (relative to the fault dip angle) being higher and more concentrated across a larger slip area. Slip in this case, and the stored strain energy being released, was observed to occur as a single large magnitude event. In contrast, numerical simulations for the other faulting types showed the stresses to be more distributed across the fault plane. This results in multiple slip events involving smaller slip areas and therefore with smaller event magnitudes, assuming all other factors are kept the same.

Fault Slip Model of the 2018 Mw 6.6 Hokkaido Eastern Iburi, Japan, Earthquake Estimated from Satellite Radar and GPS Measurements

In this study, Sentinel-1 and Advanced Land Observation Satellite-2 (ALOS-2) interferometric synthetic aperture radar (InSAR) and global positioning system (GPS) data were used to jointly determine the source parameters and fault slip distribution of the Mw 6.6 Hokkaido eastern Iburi, Japan, earthquake that occurred on 5 September 2018. The coseismic deformation map obtained from the ascending and descending Sentinel-1 and ALOS-2 InSAR data and GPS data is consistent with a thrust faulting event. A comparison between the InSAR-observed and GPS-projected line-of-sight (LOS) deformation suggests that descending Sentinel-1 track T046D, descending ALOS-2 track P018D, and ascending ALOS-2 track P112A and GPS data can be used to invert for the source parameters. The results of a nonlinear inversion show that the seismogenic fault is a blind NNW-trending (strike angle ~347.2°), east-dipping (dip angle ~79.6°) thrust fault. On the basis of the optimal fault geometry model, the fault slip distribution jointly inverted from the three datasets reveals that a significant slip area extends 30 km along the strike and 25 km in the downdip direction, and the peak slip magnitude can approach 0.53 m at a depth of 15.5 km. The estimated geodetic moment magnitude released by the distributed slip model is 6.16 × 10 18 N · m , equivalent to an event magnitude of Mw 6.50, which is slightly smaller than the estimates of focal mechanism solutions. According to the Coulomb stress change at the surrounding faults, more attention should be paid to potential earthquake disasters in this region in the near future. In consideration of the possibility of multi-fault rupture and complexity of regional geologic framework, the refined distributed slip and seismogenic mechanism of this deep reverse faulting should be investigated with multi-disciplinary (e.g., geodetic, seismic, and geological) data in further studies.

Bayesian Dynamic Finite‐Fault Inversion: 1. Method and Synthetic Test

AbstractDynamic earthquake source inversions aim to determine the spatial distribution of initial stress and friction parameters leading to dynamic rupture models that reproduce observed ground motion data. Such inversions are challenging, particularly due to their high computational burden; thus, so far, only few attempts have been made. Using a highly efficient rupture simulation code, we introduce a novel method to generate a representative sample of acceptable dynamic models from which dynamic source parameters and their uncertainties can be assessed. The method assumes a linear slip‐weakening friction law and spatially variable prestress, strength, and characteristic slip‐weakening distance along the fault. The inverse problem is formulated in a Bayesian framework, and the posterior probability density function is sampled using the Parallel Tempering Monte Carlo algorithm. The forward solver combines a 3‐D finite difference code for dynamic rupture simulation on a simplified geometry to compute slip rates and precalculated Green's functions to compute ground motions. We demonstrate the performance of the proposed method on a community benchmark test for source inversion. We find that the dynamic parameters are resolved well within the uncertainty, especially in areas of large slip. The overall relative uncertainty of the dynamic parameters is rather large, reaching ~50% of the averaged values. In contrast, the kinematic rupture parameters (rupture times, rise times, and slip values), also well resolved, have relatively lower uncertainties of ~10%. We conclude that incorporating physics‐based constraints, such as an adequate friction law, may serve also as an effective constraint on the rupture kinematics in finite‐fault inversions.

Resolving Teleseismic Earthquake Catalog and InSAR Data Discrepancies in Absolute Space to Explore Rupture Complexity Along the Ecuadorian Megathrust Fault

AbstractThe 2016 MW 7.8 Pedernales, Ecuador, megathrust earthquake produced notable crustal deformation and generated an extensive aftershock sequence that included two M6.5+ events. We combine an improved teleseismic earthquake catalog for Ecuador with analysis of coseismic interferometric synthetic aperture radar data derived from the Sentinel‐1A satellite to better delineate the spatial and temporal slip history of the megathrust fault in absolute space. The revised teleseismic catalog spans 1961‐2016 and incorporates catalog phase onset times and waveform correlation derived differential times to locate earthquakes. Using teleseismic double‐difference (DD) tomography to simultaneously solve for an updated regional 3‐D compressional velocity model and locations yields earthquakes shifted ~25 km southwest relative to rapidly available teleseismic catalogs. The DD catalog better compares in absolute space to the Ecuadorian local catalog and better models the measured deformation fields of the 2016 Pedernales mainshock and largest aftershocks. Additionally, the DD mainshock location agrees with local‐scale seismic and geodetic studies that show the 2016 event had concentrated slip on a highly coupled asperity that likely participated in the 1942 Ecuador megathrust earthquake. The two large aftershocks also ruptured on the megathrust where moderate to strong interseismic coupling is observed. The DD catalog contains moderate‐sized aftershocks that concentrate outside high slip regions, primarily in areas that produced earthquakes during the interseismic cycle, and outside areas of aseismic slip. Development of rapid relative location approaches linking new seismicity to better constrained global catalogs could aid with near real‐time hazard assessment in areas lacking local data.

Wall-bounded flow over a realistically rough superhydrophobic surface

Direct numerical simulation (DNS) is performed for two wall-bounded flow configurations: laminar Couette flow at $Re=740$ and turbulent channel flow at $Re_{\unicode[STIX]{x1D70F}}=180$, where $\unicode[STIX]{x1D70F}$ is the shear stress at the wall. The top wall is smooth and the bottom wall is a realistically rough superhydrophobic surface (SHS), generated from a three-dimensional surface profile measurement. The air–water interface, which is assumed to be flat, is simulated using the volume-of-fluid (VOF) approach. The two flow cases are studied with varying interface heights $h$ to understand its effect on slip and drag reduction ($DR$). For the laminar Couette flow case, the presence of the surface roughness is felt up to $40\,\%$ of the channel height in the wall-normal direction. Nonlinear dependence of $DR$ on $h$ is observed with three distinct regions. A nonlinear curve fit is obtained for gas fraction $\unicode[STIX]{x1D719}_{g}$ as a function of $h$, where $\unicode[STIX]{x1D719}_{g}$ determines the amount of slip area exposed to the flow. A power law fit is obtained from the data for the effective slip length as a function of $\unicode[STIX]{x1D719}_{g}$ and is compared to those derived for structured geometry. For the turbulent channel flow, statistics of the flow field are compared to that of a smooth wall to understand the effects of roughness and $h$. Four cases are simulated ranging from fully wetted to fully covered and two intermediate regions in between. Scaling laws for slip length, slip velocity, roughness function and $DR$ are obtained for different penetration depths and are compared to past work for structured geometry. $DR$ is shown to depend on a competing effect between slip velocity and turbulent losses due to the Reynolds shear stress contribution. Presence of trapped air in the cavities significantly alters near-wall flow physics where we examine near-wall structures and propose a physical mechanism for their behaviour. The fully wetted roughness increases the peak value of turbulent intensities, whereas the presence of the interface suppresses them. The pressure fluctuations have competing contributions between turbulent pressure fluctuations and stagnation due to asperities, the near-wall structure is altered and breaks down with increasing slip. Overall, there exists a competing effect between the interface and the asperities, the interface suppresses turbulence whereas the asperities enhance them. The present work demonstrates DNS over a realistic multiphase SHS for the first time, to the best of our knowledge.

Dynamic Source Model for the 2011 Tohoku Earthquake in a Wide Period Range Combining Slip Reactivation with the Short-Period Ground Motion Generation Process

This paper describes a validated dynamic rupture model of the 2011 Tohoku earthquake that reproduces both long-period (20–100 s) and short-period (3–20 s) ground motions. In order to reproduce the observed large slip area (slip asperity), we assign a large Dc (slip critical distance) area following kinematic source inversion results. Sufficiently large slip is achieved through rupture reactivation by the double-slip-weakening friction model. In order to reproduce the strong-motion generation areas (SMGAs), we assign short Dc and large stress-drop areas following empirical Green’s function (EGF) simulation results, which indicate that, although more distant from the hypocenter, SMGA1 ruptured earlier than SMGA2 or SMGA3, which are closer to the hypocenter. This observation is confirmed by the backprojection method. In order to reproduce this important feature in dynamic simulation results, we introduce a chain of small high stress-drop patches between the hypocenter and SMGA1. By systematic adjustment of stress drops and Dc, the rupture reproduces the observed sequence and timing of SMGA ruptures and the final slip derived by kinematic models. This model also reproduces the multiseismic wavefront observed from strong ground motion data recorded along the Pacific coast of the Tohoku region. We compare the velocity waveforms recorded at rock sites along the coastline with one-dimensional (1D) synthetic seismograms for periods of 20–100 s. The fit is very good at stations in the northern and central areas of Tohoku. We also perform finite-difference method (FDM) simulations for periods of 3–20 s, and confirm that our dynamic model also reproduces wave envelopes. Overall, we are able to validate the rupture process of the Tohoku earthquake.

Modeling violent rock failures in tunneling and shaft boring based on energy balance calculations

Excavation in highly stressed grounds may lead to violent compressive failures of rock or violent slip along discontinuities in the vicinity of the underground space. Violent failures, usually with anomalous seismic signatures, are characterized with radiating excess energy during the failure, endangering the safety and productivity of the operation. This paper adopts a numerical methodology, developed in the Universal Distinct Element Code (UDEC) for quantitatively studying the occurrence and intensity of violent failures, and advances it for respective analyses in tunneling and shaft-boring operations. The methodology enables estimating the radiated energy as a measure for evaluating the occurrence and relative intensity of violent failures. We first validate the radiated energy calculation in the models against analytical solutions for the formation of a circular opening, analogous to the geometry of tunnels and shafts. After reviewing the concept of violent failures by ideal models, we explore the effects of different factors on the occurrence and intensity of violent failures caused by an excavation into brittle rock or next to a preexisting fault. Limited cases studied in this paper demonstrate that different combinations of the rock elastic modulus and post-failure response of rock and discontinuity can result in a violent failure with various intensities. Larger excavations under higher deviatoric stresses can intensify the potential violent failure mostly through expanding the rock failure zone or the slip area on the activated fault. However, as opposed to the radiated energy, using the failure zone volume and fault slip area alone may lead to underestimating or overestimating the intensity of possible violent failures in a modeling practice. The energy-based analyses outlined in this paper provide a rational yet simple means for quantitatively studying violent failures in potentially complex geological conditions and excavation layouts.

Modeling Approach for Estimation of Contact and Friction Behavior of Rolling Elements in Linear Bearings

The improvement in the positioning accuracy of machine tools necessitates reliable friction models for compensation. Friction and damping are primarily caused by mechanical contacts, and they have a wide influence on the dynamics of machine tools. Particularly in the linear motor driven axis, linear bearings induce majority of the friction; contact is observed between the ball and raceway in linear bearings. Based on the Hertzian contact theory and a tangential force model, a model is developed for the friction behavior during the contact between the ball and raceway. This model determines the stick and slip areas, and the relative velocity at the contact surface. Hence, the calculation of the friction force, its hysteresis characteristics, and the stick and slip portions becomes possible.

Mapping of interplate coupling in the Kamchatka subduction zone from variations in the earthquake size distribution

The geometry of supposed coupling zones in the Kamchatka subduction zoneis determined by the earthquake size distribution based on earlier revealed relationship between its shape and rate of inelastic deformations. In the areas of higher aseismic slip, a break of linearity in earthquake size distribution is observed owing to the deficit of large earthquakes. Zones of higher coupling between the oceanic and continental plates are characterized by an excess of large earthquakes and an inverse bend in the earthquake size distribution. The mapping results of the bend value agree with the coupling zones distinguished from satellite geodetic data and inversion of marigrams.

Going to Any Lengths: Solving for Fault Size and Fractal Slip for the 2016, Mw 6.2 Central Tottori Earthquake, Japan, Using a Transdimensional Inversion Scheme

AbstractMany earthquake properties, including slip, show self‐similar (fractal) features. We can incorporate self‐similarity into Bayesian slip inversions via von Karman correlation, so that the regularization applied is representative of observed fault features. In von Karman regularization, each slip patch has a relationship to every other patch. This means that von Karman regularization only has meaning when applied to patches that actually slipped; if applied to nonslipping patches, spurious slip can be added to meet the von Karman correlation criteria. Additionally, the fault size, usually chosen in advance, also affects the von Karman correlation lengths meaning that the final slip solution may be biased by initial geometry choices. Here we present a method for solving for the size of the fault plane during the slip inversion process, as well as slip, rake, and a hyperparameter controlling slip variance. We use a transdimensional Bayesian inversion scheme constrained by geodetic surface displacements and regularized using von Karman correlation. We use circular harmonics to solve for the size of the slipping area, to allow for a complex shape that is connected and continuous across the fault. We apply this method to the 2016 Mw 6.2 Central Tottori earthquake, Japan, constrained by interferometric synthetic aperture radar InSAR (Sentinel‐1 and ALOS‐2) and Global Navigation Satellite System data (GNSS). We find an area of slip extending from approximately 2‐ to 10‐km depth, with the slipping area elongated in the downdip direction. In contrast to some seismic studies, we find slip ruptured most of the seismogenic layer.

Coseismic and Postseismic Deformation of the 2016 MW 6.2 Lampa Earthquake, Southern Peru, Constrained by Interferometric Synthetic Aperture Radar

AbstractWe use Sentinel‐1 radar imagery to explore the coseismic and postseismic surface displacements associated with the 2016 MW 6.2 Lampa earthquake in southern Peru. Based on coseismic interferograms, the preferred slip model links to a blind south southeast striking, south southwest dipping normal fault with a shallow dip (45.2°) and a peak slip of 0.71 m at depth ~5.3 km, which is consistent with seismic solutions. Postseismic interferograms, derived from two tracks of the Sentinel‐1A/B satellites using a small baseline subset method, show subsidence up to ~3 cm in the first year after the mainshock. The kinematic inversions of interferometric synthetic aperture radar (InSAR) observations imply that the postseismic surface displacements observed in 1 year after the earthquake are governed by afterslip occurring along the updip extension of the coseismic slip patches. To further improve the data fitting, we generate a fault with variable strike to refine the kinematic afterslip model. The stress‐driven afterslip forward modeling shows that the postseismic deformation is controlled by afterslip distributed at the edge of the compact coseismic slip area. The surface displacement predictions of the poroelastic rebound show subsidence of the hanging wall, but the magnitude of the displacements is small compared to the observed signal. We as well test a collection of viscoelastic relaxation models and find that the predicted surface displacements are not consistent with the observations. The InSAR results show that the strike of the seismogenic fault is quasi‐parallel to the Vilcanota normal fault system and both the fault associated with earthquake and Vilcanota normal fault dip in the same direction. Therefore, we suspect that the causative fault of this 2016 event may be a normal fault belonging to a “domino” faulting system.

Dynamics of the Motion of an Elastic Cylinder Along an Elastic Foundation

The quasi-static plane-parallel motion of an infinite elastic cylinder along a horizontal foundation made of the same material is studied (the cylinder axis is horizontal). The distribution of normal and tangential stresses in the region of contact interaction between the cylinder and plane is derived from the solution to the problem of the theory of elasticity, where the Amontons-Coulomb dry friction model is used in the slip area and the presence of a stick area is taken into account. The analytic solution to the problem is obtained and the phase portrait of the system is drawn. We compare this with the problem of the motion of a perfectly rigid cylinder along a rigid surface with dry friction and without slip.

Monitoring and modelling of false brinelling for railway bearings

An adaptive finite element model was developed to predict false brinelling in a cylindrical bearing, during the transportation of new trains and then compared with experimental measurements. The model was developed, based on the Archard wear equation, using ABAQUS and developing an ABAQUS UMESHMOTION code. A false brinelling monitoring system was designed and installed to record the vibration and rotational motion of the bearing, during the train's road and sea transportations and were used as inputs for the FE model. A set of laboratory experiments were conducted to determine wear and friction coefficients and the threshold energy for the bearing that were used in the simulation process. To compare the FE results with a real case, a profilometry measurement of false brinelling marks in a damaged bearing was performed.According to the FE wear profile results, rotational displacement of the bearing is the most likely cause for false brinelling during transportation. Due to the wear energy being below the threshold, it was predicted that no false brinelling occurred due to lateral and axial vibrations at the roller. The existence of the partial slip area, in the contact, causes the development of W shape wear marks that was seen in the profilometry measurement of the damaged sample.