Maximum Slip Research Articles

Multi-Sensor Geodetic Observations and Modeling of the 2017 Mw 6.3 Jinghe Earthquake

The Mw 6.3 Jinghe earthquake struck Xingjiang Province, China, on 8 August 2017 (05:15:04 UTC); the epicenter was near the Kusongmuxieke Piedmont Fault (KPF) of the northern Tian Shan Mountains. We used multi-source and multi-track satellite Synthetic Aperture Radar (SAR) imagery and Interferometric SAR (InSAR) techniques to reconstruct the coseismic displacement field from different line-of-sight geometries. To reduce the phase artifacts, we employed multi-temporal scenes acquired by Sentinel-1, and reconstructed the coseismic deformation through a temporal averaging strategy. Together with a single interferometric pair obtained using the Phased Array type L-band Synthetic Aperture Radar 2 (PALSAR2) sensor aboard the Advanced Land Observing Satellite 2 (ALOS2), we obtained five displacement maps with slightly different viewing geometries; all of which were used to constrain a geodetic inversion to retrieve the fault geometry parameters and slip distribution. Based on the focal mechanism and regional geology, we constructed multiple fault models that differ in dip direction (south and north dipping), and various striking angles. Both models fit the InSAR displacement maps, but have slip distributions of different depths. The slip depth of the south dipping model, with a dip of ~42°, is the most consistent with the relocated earthquake sequence and regional geological structure. Through the geodetic inversion, the maximum slip (0.25 m) occurred at 14.05 km and the associated rake was 89.56°. The result implies that the seismogenic fault is a blind thrust fault north of KPF (towards the foreland). Considering the relative locations of the suggested blind fault, the KPF, and the continuing north to south (N–S) shortening of the Tian Shan Mountains, this fault could be formed by the northward propagation of the regional fold-thrust belt.

Forced Convection Heat Transfer of a Giesekus Fluid in Circular Micro-Channels Subjected to a Constant Wall Temperature

Abstract In this paper, an exact analytical solution for forced convective heat transfer of nonlinear viscoelastic fluid in isothermal circular micro-channel is presented. The nonlinear Giesekus constitutive equation is used to model the Giesekus fluid heat transfer in micro-channel with constant wall temperature, which is the main innovative aspect of the current study. This constitutive equation is a powerful tool and able to model the fractional viscometric functions, extensional viscosity, and elastic property. The solution of temperature profile and Nusselt number is obtained based on the Frobenius method. The effects of Weissenberg number, mobility factor, slip coefficient, and Navier index on temperature distribution, velocity profile, and Nusselt number are investigated in detail. The results show that the increases in both slip coefficient and Navier index cause the increases in slip velocity and maximum dimensionless temperature at the wall and the micro-channel center, respectively. Moreover, the Nusselt number has an upward trend with increases in slip coefficient and Navier index parameters. The results are indicated that the flow and temperature fields have a complex relation with mobility factor which controls the level of the nonlinearity of the Giesekus model. Additionally, three correlations for Nusselt number of Giesekus flow in micro-channel are presented.

Experimental Investigation of a Slip in High-Performance Steel-Concrete Small Box Girder with Different Combinations of Group Studs.

Due to the significant advantages of steel-concrete composite beams, they are widely used for accelerated bridge construction (ABC). However, there is still a lack of experimental research on the proper design of ABC, especially in the slip with a different group of shear connectors. As a component of steel-concrete composite structure, shear studs play a vital role in the performance of composite structures. This paper investigates the influence of group studs in simply supported and continuous box girders. To this end, three sets of simply supported steel-concrete composite small box girders and two continuous steel-concrete composite small box girders were made with different groups of shear studs, and the slip generated along the beams was recorded under different caseloads. The results were then compared with the proposed simplified equations. The results show that the slip value of the test beam is inversely proportional to the degree of shear connection. The slip of Simply Supported Prefabricated Beam-3 (SPB3) is 1.247 times more than Simply Supported Prefabricated Beam-1 (SPB1), and 2.023 times more than Simply Supported Prifabricated Beam-2 (SPB2). Also, the slip value of Experimental Continuous Beam-1 (ECB1) is 1.952 times more than Experimental Continuous Beam-2 (ECB2). The higher the degree of shear connection, the smaller the maximum slip value.

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 Effects of Grain Size and Strain Amplitude on Persistent Slip Band Formation and Fatigue Crack Initiation

The maximum persistent slip band (PSB) width in cyclic loading is experimentally proven to be a material property in this paper. The dependence of the maximum PSB width on grain size, selected as a microstructural property of the material, is tested and reported. The effect of strain conditions, which conversely is not a material property of copper, is also included in the study. The results demonstrate that the maximum PSB width of annealed copper (grain size = 104.2 µm) is statistically the same within this class of grains, and is statistically larger than that of the stress-relieved copper (grain size = 14.2 µm). In contrast, the PSB width evolution is not sensitive to different strain conditions. These findings advance the fundamental understanding of how persistent slip band formation is influenced by variations in fatigue mechanical stimulus and metallurgical characteristics.

Automatic tractor slip-draft embedded control system

A microcontroller-based embedded system for automatic slip-draft control was designed, developed and tested for a 2WD tractor. The system synchronously measures and controls the wheel slip and implement′s draft closer to the set ranges under varying field conditions. Actual and theoretical speeds were digitally acquired through the controller-Hall Effect combination employed on front and rear wheels for the digital accession of the wheel slip. Implement draft was recorded using a three-point linkage dynamometer placed between the tractor and implement. The developed system was evaluated with test tractor and analogized with the existing draft control system. A maximum slip variation of 2% was witnessed between the computed and the indicated values in the developed system. The novel intelligent slip-draft control system also amounted to improve the tractive performance of 9.17% and 6.05% during ploughing and harrowing respectively when analyzed against an existing draft control system. It also minimizes operator fatigue and improves the operation efficiency resulting from a minimum intervention for depth and draft control under dynamic field conditions.

Slow-slip, slow earthquakes, period-two cycles, full and partial ruptures, and deterministic chaos in a single asperity fault

The assimilation of geological, geophysical, and laboratory data in physics-based models of fault dynamics promises increasingly realistic simulations of the seismic cycle. To assist this effort, I explore the dynamics of a single velocity-weakening asperity to delineate the relationship between a fault physical properties and the style of faulting during the seismic cycle based on a micro-physical model of rate-and-state friction. From a dimensional analysis, four non-dimensional parameters control the characteristics of slip events and the behavior during the interseismic period, including the Dieterich-Ruina-Rice number Ru, which is proportional to the ratio of asperity to critical nucleation size W/h*, and Rb = (b − a)/b, where a and b control the direct and local evolutionary effects, respectively. For sufficiently large Rb, the Ru number controls the spectrum of fault slip, from periodic slow-slip events to aperiodic fast ruptures. In finite faults, but not in semi-infinite faults, the transition between these end-members includes a bifurcation that involves period-two, period-four, period-six cycles, and deterministic chaos with increasing Ru. Macroscopic fault slip is stabilized as Rb vanishes, even as Ru ≫ 1. For finite faults, but not for semi-infinite faults, the transition between slow and fast ruptures for increasing Rb includes another type of bifurcation with period-two and period-four cycles of slow and fast ruptures. For 0 <Rb ≪ 1 and Ru ≫ 1, slow ruptures become chaotic, characterized by aperiodic bursts of slow earthquakes within a longer slow-slip episode. The third non-dimensional parameter is a cut-off velocity that affects the maximum slip speed. The static friction coefficient μ0 strongly affects the rupture style, as fault strength provides an upper bound for stress drop. Many styles of instabilities and interseismic behaviors emerge depending on the coordinates in phase space, most importantly Ru and Rb. Combining complementary observations at different stages of the seismic cycle may offer an opportunity to infer these parameters in nature.

Fault models for the Bodrum–Kos tsunamigenic earthquake (Mw6.6) of 20 July 2017 in the east Aegean Sea

We investigate a fault model for the shallow, strong (Mw6.6) tsunamigenic earthquake of 20 July 2017 with source area in the east Aegean Sea between Bodrum peninsula (Turkey) and Kos Isl. (Greece). Fault plane solutions are consistent with the regional active tectonics indicating normal faulting striking about E–W. A relocated hypocenter of the main shock was obtained and the rupture time-space history for two alternative fault solutions dipping either to the south or to north was approached by inverting P-waves recorded at teleseismic (30°–90°) distances. In both fault solutions the seismic moment calculated corresponds to magnitude Mw = 6.6 while the earthquake had total rupture duration of less than 10 s. The maximum co-seismic slip was close to the hypocenter ∼1.6 m and ∼2.2 m for the south and north dipping faults, respectively. Close to the surface co-seismic slip of ∼0.3 m was calculated. Our analysis of Sentinel satellite InSAR images showed ground deformation fringes indicating ∼13 cm vertical displacement change between the North and South coasts of the Karaada islet. This result is in line with our preference of the south dipping fault, supported primarily by GPS displacements, regional tectonics, aftershock activity and tsunami observations, although results of InSAR inversion fit equally well both solutions.

Fluid driven shear cracks on a strengthening rate-and-state frictional fault

This study is dedicated to the dynamics of slow slip (or creep) reactivation on faults stimulated by a fluid injection. Fluid driven slow slip events involving slip rates too small to generate detectable elastic waves (typically less than 1 cm.s−1) are commonly observed on natural faults either in tectonic active areas or in the framework of deep energy exploitation. We model the fault as a planar 2D velocity strengthening rate-and-state frictional interface embedded in an elastic medium. The fluid is injected at a constant rate and spreads diffusively along the fault reducing the effective normal stress. We show that the fluid injection initiates a shear crack on the fault. In a first phase, the shear crack remains confined to the pressurized zone, and slip-rate increases exponentially with time. A second phase starts at the onset of a rapid crack expansion. The shear crack during phase two expands faster than the pressurized zone. Depending on the prestress conditions, the shear crack evolves towards two different regimes. If the initial shear stress τ0 is larger than the steady-state residual frictional stress τr within the crack, the slip rate and the crack expansion rate blow up in a finite time. This accelerating crack regime is similar to the nucleation of a dynamic rupture on the fault. On the other hand, if τ0 < τr, the accelerated expansion progressively slows down so that the crack enters a steady regime, characterized by a constant expansion speed and a logarithmic increase of slip-rate. However, a large majority of fault scenarios ultimately lead to this steady expansion regime, which is also the most probable scenario on real tectonic faults. In addition to the numerical results, we develop asymptotic expressions for the maximum slip rate history on the fault and the crack length history, showing how initial prestress τ0, frictional conditions (ratio a/b), hydraulic properties and injection history control the dynamics of fluid induced aseismic slip events.

Teleseismic body wave inversion in determining rupture process of Sumbawa doublet earthquake, November 25th, 2007

The rupture patterns of the Sumbawa doublet earthquake that occurred on November 25th, 2007 was estimated using teleseismic body wave inversion. The first event occurred at 16:02:18 UTC with epicenter at 8.292°N and 118.37°E, short after this, the second event occurred at 19:53:08 UTC with epicenter at -8.224°N and 118.467°E. For each event, teleseismic body wave data were retrieved from the Incorporated Research Institutions for Seismology – Data Management Center (IRIS-DMC). The waves were windowed for 70 s which started at 20 s before the P-wave arrival, band-pass filtered between 0. 01 and 0.1 Hz and then integrated into a displacement with a sampling time of 0.5 s. The Green’s function is calculated using the Kikuchi and Kanamori method. The fault geometry is based on the earthquake parameters of the Global Centroid Moment Tensor solution. Strike and dip for first event were 88° and 23°, respectively and those for the second event were 87° and 25°, respectively. The seismic moment (Mo) estimated by the inversion for the first event is 0.617×1019 Nm or equivalent to moment magnitude (Mw) 6.46 with source duration of approximately 55 s. While for the second event, the seismic moment is estimated to be 0.644×1019 Nm (Mw 6.47), with slightly longer source duration. The inversion for both events provided a similar slip pattern. The rupture propagated along the dip direction, and the maximum slip occurred near the hypocenter region. The maximum slip amount for first event and second event were 1.43 m and 1.48 m, respectively.

Deformation profile and interface-mediated defect interaction in Cu/CuZr nanolaminates: An effective-temperature description

Both simulations and experiments have suggested that Cu/CuZr nanolaminates are stronger and more ductile than their individual constituents due to interface-mediated interactions between plasticity carriers. In this work, we use the effective-temperature theories of dislocation and amorphous shear-transformation-zone (STZ) plasticity to study amorphous-crystalline interface (ACI)-mediated plasticity in Cu/CuZr nanolaminates under mechanical straining. The model is shown to capture reasonably well the measured deformation response when strained either in tension parallel to or in compression normal to the amorphous-crystalline interface. Our analysis indicates that increasing CuZr or decreasing Cu layer thickness increases the maximum flow stress for both perpendicular and parallel loading cases. For the cases of parallel and perpendicular loading, the maximum flow stress values are 3.4 and $2.5\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, respectively. Furthermore, increasing the strain rate for the parallel loading case decreases the slip strain in the amorphous and crystalline layers. For the perpendicular loading case, an increase in strain rate decreases the amorphous layer slip but increases the crystalline layer slip. In all slip strain analyses, maximum slip strain occurs at the ACI, thus indicating that plasticity carriers accumulate at the interface and are absorbed there. These findings indicate a significant anisotropy in strength with greater sensitivity to layer thickness for the case of tensile loading parallel to the ACI. Further findings signify that slip strain is more sensitive when the nanolaminate is compressed perpendicular to the ACI.

Coseismic changes in subsurface structure associated with the 2018 Hokkaido Eastern Iburi Earthquake detected using autocorrelation analysis of ambient seismic noise

Autocorrelation analysis using ambient noise is a useful method to detect temporal changes in wave velocity and scattering property. In this study, we investigated the temporal changes in seismic wave velocity and scattering property in the focal region of the 2018 Hokkaido Eastern Iburi Earthquake. The autocorrelation function (ACF) was calculated by processing with bandpass filters to enhance 1–2 Hz frequency range, with aftershock removal, and applying the one-bit correlation technique. The stretching method was used to detect the seismic wave velocity change. After the mainshock, seismic velocity reductions were observed at many stations. At N.AMAH and ATSUMA, which are located close to the mainshock, we detected 2–3% decreases in seismic wave velocity. We compared parameters indicating strong ground motion and showed the possibility of correlations with peak dynamic strain and seismic velocity reduction. We also investigated the relationship between waveform correlation and lag time, using ACFs from before and after the mainshock, and detected distortion of the ACF waveform. The source of the waveform decorrelation was estimated to be located near the maximum coseismic slip, at around 30 km depth. Thus, distortion of the ACF waveform may reflect the formation of cracks, due to faulting at approximately 30 km depth.

The 2016 M7 Kumamoto, Japan, Earthquake Slip Field Derived From a Joint Inversion of Differential Lidar Topography, Optical Correlation, and InSAR Surface Displacements

AbstractObservations of surface deformation within 1–2 km of a surface rupture contain invaluable information about the coseismic behavior of the shallow crust. We investigate the oblique strike‐slip 2016 M7 Kumamoto, Japan, earthquake, which ruptured the Futagawa‐Hinagu Fault. We solve for variable fault slip in an inversion of differential lidar topography, satellite optical image correlation, and Interferometric Synthetic Aperture Radar (InSAR)‐derived surface displacements. The near‐fault differential lidar pose several challenges. The model fault geometry must follow the surface trace at the sub‐kilometer scale. Integration of displacement datasets with different sensitivities to the 3D deformation field and varying spatial distribution permits additional complexity in the inferred slip but introduces ambiguity that requires careful selection of the regularization. We infer a Mw earthquake. The maximum slip of 6.9 m occurred at 4.5‐km depth, suggesting an on‐fault slip deficit in the upper several kilometers of the crust that likely reflects distributed and inelastic deformation within the shallow fault zone.

Shallow intraplate seismicity related to the Illapel 2015 Mw 8.4 earthquake: Implications from the seismic source

The September 16, 2015, Mw 8.4 Illapel, Chile earthquake is the first large event occurring in north-central Chile after the 1943 earthquake, filling a known seismic gap in the region. The earthquake took place in a complex tectonic region, nearby an area where transition from erosive to accretionary margin occurs due to the collision of Juan Fernandez Ridge (JFR) along the Chilean margin. We inverted the kinematic rupture process of the 2015 Mw 8.4 Illapel earthquake from the joint inversion of teleseismic body waves and near-field data. The relative weighting between datasets and the weighting of spatial/temporal constraints are objectively estimated by applying the Akaike's Bayesian Information Criterion. The coseismic slip model yields a total seismic moment of 4.92 × 1021 Nm occurred over ~120 s. The rupture shows both downdip and updip propagation with slip extending along the thrust interface from ~50 km depth to shallow near-trench depths (<15 km), with maximum slip of ~9 m located at shallow depths, where low average rupture speeds ~1.8–2 km/s are estimated. Outer-rise events, triggered within the oceanic Nazca plate after the mainshock, did not penetrate into the mantle and are related to preexisting faults due to both bending of Nazca plate and JFR uplift, which promotes a tensional stress regime in the surrounding area. This seismicity was triggered by static stress transfer from near-trench slip revealed by our source rupture modelling, suggesting outer-rise seismicity as a proxy for near-trench coseismic slip. Crustal seismicity within continental South American plate is observed prior to, and after, the mainshock, mainly related to extensional faulting within eroded and fractured wedge due to tectonic processes along erosive margins. We also show evidence of shallow seismicity after the mainshock associated with a long-lived crustal fault, which can represent a high seismic hazard for La Serena-Coquimbo conurbation.

The 2018 Mw 7.5 Palu Earthquake: A Supershear Rupture Event Constrained by InSAR and Broadband Regional Seismograms

The 28 September 2018 Mw 7.5 Palu earthquake occurred at a triple junction zone where the Philippine Sea, Australian, and Sunda plates are convergent. Here, we utilized Advanced Land Observing Satellite-2 (ALOS-2) interferometry synthetic aperture radar (InSAR) data together with broadband regional seismograms to investigate the source geometry and rupture kinematics of this earthquake. Results showed that the 2018 Palu earthquake ruptured a fault plane with a relatively steep dip angle of ~85°. The preferred rupture model demonstrated that the earthquake was a supershear event from early on, with an average rupture speed of 4.1 km/s, which is different from the common supershear events that typically show an initial subshear rupture. The rupture expanded rapidly (~4.1 km/s) from the hypocenter and propagated bilaterally towards the north and south along the strike direction during the first 8 s, and then to the south. Four visible asperities were ruptured during the slip pulse propagation, which resulted in four significant deformation lobes in the coseismic interferogram. The maximum slip of 6.5 m was observed to the south of the city of Palu, and the total seismic moment released within 40 s was 2.64 × 1020 N·m, which was equivalent to Mw 7.55. Our results shed some light on the transtensional tectonism in Sulawesi, given that the 2018 Palu earthquake was dominated by left-lateral strike slip (slip maxima is 6.2 m) and that some significant normal faulting components (slip maxima is ~3 m) were resolved as well.

Inversion of the rupture process and high-frequency radiation of the 2017 Jiuzhaigou earthquake, northeastern Tibetan Plateau

We studied the low- and high-frequency source processes of the 2017 Jiuzhaigou earthquake, and focused on when and where the high-frequency (2.0–10.0 Hz) seismic energy was radiated in relation to the low-frequency (0.02–0.5 Hz) seismic energy. The low-frequency source processes were jointly inverted using teleseismic P and SH broadband waves combined with near-field strong motion data. A three-dimensional model considering real topography was used to compute the near-field Green’s function. The high-frequency wave radiation was inversed using the envelope of acceleration seismograms of near-field records and the empirical Green’s function by the differential evolution algorithm. The results showed the 2017 Jiuzhaigou earthquake was a typical strike-slip earthquake with a seismic moment of about 6.9 × 1018 N m and maximum slip of about 1.5 m. During the 2 s following the initial rupture, the earthquake radiated large high-frequency waves but small low-frequency waves. Then, the rupture broke the high stress drop area in the up-dip direction of the hypocenter, generating an obvious asperity located just above the hypocenter. About 60% of the seismic moment of the earthquake was released during about 2–6 s after initiation of the rupture. The high-frequency radiation areas were mostly located on the lower periphery of the asperity, in accordance with the complementary relationship between the distribution of high-frequency waves and zones of large slip, which might be attributable to both the initiation of the rupture and the breaking of the high stress drop area. Parts of the high-frequency radiation areas overlapped the lower part of the asperity, where the high-frequency radiation occurred about 2 s earlier than the low-frequency radiation. The stress drop of the 2017 Jiuzhaigou earthquake was considerably lower than average for global intraplate earthquakes, but similar to that of the 2013 Lushan earthquake.

Dynamic modeling of bedding-plane slip during hydraulic fracturing

Whether the tip stresses around a dynamically propagating hydraulic fracture (HF) could activate a bedding plane (BP) or not is an important question for HF propagation and microseismicity generation. BP slip has been proposed to be one main source of microseismicity during HF treatments in unconventional reservoirs. However, a BP perpendicular to a principal stress direction is unlikely to be activated in a simple geomechanical model. We have applied a dynamic finite-element geomechanics method to examine the induced dynamic shear stress and the activation of BPs that are perpendicular to the HF based on the Cotton-Valley tight-sand reservoir properties. We work in a 2D vertical-plane framework. The induced dynamic stresses around a HF tip could be significant. We explore three different scenarios for the BP activation. In the first scenario, an HF is dynamically propagating toward two symmetric BPs, but has not touched them yet. We find that only low-strength BPs can be activated in this scenario. In the second scenario, an HF dynamically propagates toward two symmetric BPs and then it crosses them by a short distance. The BPs could be more easily activated in this scenario compared with the first scenario. The slip length and maximum slip decrease with cohesion, critical slip distance, or maximum principal stress. In the third scenario, an HF dynamically propagates toward two symmetric BPs, and then fluid invasion into the BPs occurs after the HF touches them. Large shear slippage and slip length happen in this scenario because fluid invasion weakens the BPs. In all of the scenarios, different senses of shear could occur along the BPs and a rupture typically propagates bilaterally from the initiation point on the BPs.

Rupture of the Indian slab in the 2011 Mw 6.9 Sikkim Himalaya earthquake and its tectonic implications

Unlike the other Himalayan plate boundary segments, the eastern Nepal to Bhutan Himalayan region is not known to have generated prominent shallow thrust faulting earthquakes, typical of the ongoing convergence. This region features strike-slip earthquakes over the depth ranges of 40�120 km, indicating intraslab deformation. Here we present for the first time a slip distribution model for the largest recorded intraslab strike-slip earthquake in this region, the Mw 6.9 Sikkim event that occurred on 18 September 2011. Relying on kinematic source process modeling, our results indicate a NE-SW trending, steeply dipping sinistral source zone within the underthrusting Indian slab. The rupture propagated radially, with a low rupture velocity of 1.7 km/s, breaking a large asperity of 20 A� 20 km 2 with a maximum slip of 1.6 m. The rupture nucleated at a depth of 45 km and reached upper mantle depths. The computed coseismic stress drop value is 13.6 MPa. We suggest that most of the aftershocks occurred on the conjugate plane, possibly due to stress triggering. Stress inversion of focal mechanisms indicates a transpressive stress regime throughout the crust and pure strike-slip regime in the upper mantle. We observed a unimodal distribution of earthquakes beneath the Higher Himalaya. This indicates a strong, brittle Indian slab and unravels a scenario of an eventual breakup of the lithosphere; the key trigger might be variation in the convergence rates along the Himalayan arc. ©2019. American Geophysical Union. All Rights Reserved.

Geodetic Observations of the 2018 Mw 7.5 Sulawesi Earthquake and Its Implications for the Kinematics of the Palu Fault

AbstractThe ascending and descending interferometric synthetic aperture radar data are used to investigate the fault rupture and slip model of the 2018 Mw 7.5 Sulawesi, Indonesia, earthquake. The best fitting slip model indicates that this earthquake ruptured not only a segment extending the Palu fault to the north but also a northwestern segment offshore. The slip on the onshore fault is predominant left‐lateral strike slip. The slip on the offshore fault is dominated by normal faulting with a maximum slip of ~6.3 m. The newly discovered offshore normal faulting is likely to be the cause of the tsunami after the shock. Combined with previous geomorphic, tectonic, geodetic, and modeling studies, we suggest that the kinematics of the Palu fault maintained the same style of faulting from north to south, which resulted from an oblique extension occurred on an east dipping fault at depths. The deformation pattern of NW Sulawesi is dominated by this slip mechanism.

On the early-age bond-slip behavior of an eccentric bar embedded in a grouted sleeve

Grouted-sleeve connections are widely used to connect prefabricated concrete members. The bond stress-slip behavior is an essential issue to be considered when assessing the performance of a grouted-sleeve connection loaded in tension. This paper presents an experimental investigation regarding the local and global bond stress-slip behavior of grouted-sleeve connections. Three parameters were investigated: the embedment length, construction eccentricity, and loading time after grouting, respectively. The specimens were subjected to a monotonic tensile load, and the slip between the bar and the grouted-sleeve was measured during the test. Moreover, to evaluate the confinement effect, the circumferential strain at the surface of the grouted-sleeve was measured. The results reveal that the maximum local bond stress increases with the age of the grout, whereas it decreases as the construction eccentricity of the bar increases. Moreover, the influence of the construction eccentricity is mitigated by a longer bonded length. The load-slip relationship is approximately linear for the specimen with an embedment length-to-bar diameter ratio equal to ten, loaded at the age of seven days. Based on the experimental results, an analytical model, including the local and global bond stress-slip relationship, is proposed to evaluate the maximum slip and to describe the strain distribution in the long specimens (lb/d = 6, 10). The agreement among the experimental and calculated bond stress, the maximum slip and strain distribution at the surface of the sleeve demonstrates the validity of the proposed model.