Normal Slip Research Articles

Exploring the Dynamic Interactions Between the Southern San Andreas Fault and a Normal Fault Under the Salton Sea

AbstractWe investigate the dynamic interactions between the Southern San Andreas Fault (SSAF) and a proximal normal fault (NF) beneath the Salton Sea in southern California. The NF, positioned near the SSAF terminus at Bombay Beach, exhibits 11–15 displacement events across 14 stratigraphic sequences, with a range of 0.2–1.4 m of vertical offset since ∼2–3 ka. Notably, four of these events may align temporally with SSAF earthquakes, raising questions about the possible interplay between the two faults. Utilizing dynamic rupture models, we analyze the coseismic interactions between the SSAF and NF, addressing under what conditions the SSAF induces slip on the NF. Our findings reveal that a suite of SSAF ruptures, particularly those propagating from north to south, can trigger slip on the normal fault and replicate observed vertical offsets. If the SSAF extends beneath the Salton Sea, earthquakes originating south of the NF intersection are less likely to trigger normal fault slip, although we cannot exclude this possibility. Some SSAF ruptures do not trigger discernible slip on the NF, rendering such events undetectable in the stratigraphic record. Our research contributes toward discussions regarding the seismic hazard in southern California, shedding light on the interplay between the SSAF and NF.

A study on the fretting corrosion of 316L in static lead-bismuth eutectic (LBE): The role of slip amplitude and normal force on damage mechanism at 350 °C

Fretting corrosion of stainless steel in the LBE affects the safety of lead-cooled fast reactors. Slip amplitude and normal load are the main mechanical factors affecting fretting wear behavior. Thus, the damage mechanism of 316L stainless steel at 350 °C LBE influenced by slip amplitude and normal load was investigated by jointly utilizing multiple characterization methods. The results indicate that the normal load and slip amplitude essentially affect the tangential stress and relative sliding value in the contact area, leading to different slip regions and damage mechanisms. In the mixed slip region, the damage mechanism is adhesion and delamination cracks. The increase in tangential stress leads to decrease in relative sliding. The thick wear debris layer attached to the worn surface can protect the substrate from being attacked by the LBE. In the gross slip region, the damage mechanism is abrasive wear and dissolution corrosion. The increase in relative sliding causes more damage and Ni dissolution, leading to the transformation from austenite to ferrite and internal strain, making the substrate more susceptible to damage and increasing the risk of liquid metal embrittlement (LME) of austenitic stainless steel at 350 °C. Accordingly, a model for different damage mechanisms was proposed. These results can provide important information on the fretting damage related to the LBE environment.

Relocation of earthquake clusters show seismogenic transverse structures in the Inner Northern Apennines (Italy)

The Inner Northern Apennines (Italy) are a region with a dominant N-S to NNW-SSE fault system, but dissected and offset by several E-W to NE-SW trending structures and lineaments. The knowledge about the nature of these transverse structures, their origin, activity and role in current tectonic motions is limited and debated. To better establish the location, subsurface shape, and kinematics of faults related to the Livorno-Empoli lineament, one of the major transverse structures in the Northern Apennines, we analysed the seismicity in western Tuscany. In the Viareggio Basin we identified and relocated two distinct earthquake clusters as well as calculated 12 new focal mechanisms. The results show that the clusters consisted of several swarms from the years 2006, 2015, 2016 and 2021. The events had a depth between 2 and 15 km and were located along a NE-SW oriented, SE dipping fault system dissecting the Viareggio Basin. Focal mechanisms show oblique normal slip. We interpret the fault system to form a connection between the Viareggio Basin and the Lucca Basin to the east as well as continuing offshore. The results show that the transversal faults of the Inner Northern Apennines are seismogenic, with the length, position and onshore to offshore nature of the fault suggesting reactivation of pre-existing structures.

Forearc faults in northern Cascadia do not accommodate elastic strain driven by the megathrust seismic cycle

We employ numerical models to explore the connection between subduction zone coupling or megathrust rupture and upper plate faults in the northern Cascadia forearc. Active forearc faults north of the Olympic Peninsula exhibit similar characteristics: west-northwest strike, oblique right-lateral slip senses, and low slip rates (<1 mm/yr), but a potential to generate large (M ~ 7) earthquakes. Previous hypotheses suggest that stress in the upper plate due to interseismic coupling or coseismic rupture along the subduction zone interface could drive permanent forearc strain. To test these hypotheses, we used a 3D boundary element method model to predict slip on the LRDM if interseismic coupling or coeseismic rupture cause deformation. Our model predicts reverse left-lateral slip if the strain results solely from subduction zone coupling, or normal right-lateral slip if these faults accommodate strain during a megathrust rupture. These results contradict the observed fault kinematics. Additionally, if we use our model to mimic strain partitioning, where only the strain from the strike-slip component of subduction zone coupling is accommodated in the forearc, our results are also inconsistent observed fault kinematics. These models challenge the hypothesis that subduction zone coupling or coseismic rupture are the primary driver of permanent forearc deformation in northern Cascadia.

Correlation between geomechanical and sedimentary facies and their implications for flow unit definition in the pre-salt carbonate reservoir, Brazil

Carbonate reservoirs are of great economic importance due to their frequent association with high permeability and hydrocarbon storage capacity. One of the most significant discoveries of this type of reservoir in recent decades has been the Brazilian Pre-salt. This deep reservoir has unusual depositional features, consisting of a wide variety of textures with different compositions, influenced by diagenetic overprinting that modify most of its mechanical, elastic and petrophysical properties. Despite the marked heterogeneity, these carbonates are characterized by excellent reservoir quality. The objective of this study is to establish a correlation between geomechanical behavior and sedimentary facies and its implications for the definition of flow units in the Barra Velha Formation, the main reservoir of the Brazilian Pre-salt. Thus, using a database from the Buzios field composed of well logs (conventional and advanced), well tests, thin sections, and laboratory petrophysics, geomechanical facies (GMFs) were defined using dynamic geomechanical modeling and an unsupervised algorithm (K-mean clutering), followed by textural classification of sedimentary facies and definition of flow units (FUs) on the decametric scale. These classifications were compared using frequency histograms. The geomechanical model revealed that the in-situ stress state exhibits a dual regime, between normal and strike slip. In addition, it was found that the direction of the maximum horizontal stress is in the NE-SW azimuth. In this context, four geomechanical facies were defined, which showed a notorious variation in mechanical strength. The strongest GMFs consisted mainly of well-cemented Grainstones and Packstones with no apparent porosity or microcrystalline porosity and correlated with the FU with the worst production rates. On the other hand, the weaker GMFs were mainly composed of Grainstones and Spherulistones with high intergranular porosity generated by dissolution processes, with higher risk of pore collapse and correlated with the FUs with the best production rates. However, this classification also identified laminated mudstones with microporosities associated with FUs that act as flow barriers. Geomechanical facies have also been incorporated into reservoir development by evaluating wellbore stability, fault reactivation risk, and brittleness index for future CO2 injection projects.

Temporal evolution of shear-induced dilatancy of rock fractures: controls from surface roughness and normal stress

SUMMARY Understanding the shear-induced dilatancy of rock fractures is important for assessing the permeability evolution and seismic hazard in shale and geothermal reservoirs. The displacement dependence of fracture dilation has been well studied, while the influence of slip velocity is poorly constrained. In this study, we combined displacement- and velocity-dependent aperture models to reproduce the transient shear-induced dilatancy of fractures in sandstone in 16 normal stress unloading tests. Our results show that the combined aperture model can describe the transient fracture aperture evolution during accelerating slip induced by normal stress unloading better than the model dependent only on slip displacement. Slip velocity could enhance the aperture increase on smoother fractures at lower normal stresses and higher slip velocities. Both the dilation factor and characteristic slip distance decrease with increasing normal stress and surface roughness, signifying reduced contribution of slip velocity to transient shear-induced dilatancy at higher normal stresses and surface roughness. The dilation angle increases with the increase of surface roughness, and this increase diminishes at higher normal stresses primarily attributable to more severe asperity wear. These findings highlight the importance of slip velocity in controlling the transient evolution of aperture and permeability of a rock fracture. Our study also provides constraints on the constitutive parameters in the combined aperture model for describing transient shear-induced fracture dilatancy. We suggest that it is crucial to incorporate the velocity-dependent aperture model to simulate the nonlinear evolution of fracture aperture in future analytical and numerical models involving coupled hydromechanical processes in geoenergy systems.

Mylonite, cataclasite, and gouge: Reconstruction of mechanical heterogeneity along a low-angle normal fault: Death valley, USA

The spectrum of slip behavior in crustal faults generates various rock types that can inform the mechanics of earthquake genesis. However, a single fault exposure may contain evidence of slip at various depths and temperatures due to progressive fault rock formation and overprinting during exhumation. Here, we unravel the spatiotemporal evolution of mechanical transitions along the Boundary Canyon detachment, a low-angle normal fault northeast of Death Valley, USA. Field, microstructural, and geochemical characterizations of fault rocks are compared to existing laboratory experiments and combined with a thermo-kinematic model of fault evolution. Together, these constrain the depths of mechanical transitions along the fault and reveal the evolution of earthquake nucleation zone thickness. Fault exposures from different initial paleodepths passed through the mechanical transitions during footwall exhumation, resulting in overprinting of mylonite by cataclasite and ubiquitous late formation of foliated, illite-rich gouge within the uppermost crust. We present evidence of coseismic low-angle normal fault slip (e.g., injection veins of cataclasite, laminar and grain-inertial fluidization). Coseismic slip likely nucleated at strength contrasts within the fault zone (i.e., contacts between quartzite breccia and calc-mylonite; quartz ribbons and mylonite matrix; breccia and clay gouge) at ≈ 5–9.5 km depth. Observations including mutually overprinting cataclasite/ultramylonite and exposures of pulverized gouge support that dynamic rupture propagated down-dip through the brittle-ductile transition zone (≈10–11 km depth) and up-dip through velocity-strengthening fault patches (≈0–5 km depth). Rapid fault exhumation increased the geotherm, leading to upward advection of the brittle-ductile transition and shallowing/thinning of the earthquake nucleation zone. This process may explain the rarity of large magnitude earthquakes on low-angle normal faults.

Segmentation of the Tashkurgan normal fault in the eastern Pamir: Insights from geomorphology and thermochronology and implications for fault-slip transfer

At the northwestern end of the India–Asia collision zone, in the eastern Pamir interior, the Kongur Shan extensional system extends for ∼250 km as a composite system of normal faults. As the southernmost segment of the extensional system, the Tashkurgan fault can be divided into a northern and southern segment by the intersection of the Tahman and Tashkurgan faults. To evaluate the tectonic activity along the Tashkurgan fault and explore the extensional characteristics of the southern Kongur Shan extensional system, we integrate geomorphologic analysis with thermochronologic data and modeling. Geomorphic indices, including local relief, normalized channel steepness index (ksn), and river χ-plots, show that the southern Tashkurgan fault is more active than the northern Tashkurgan fault. On the footwall of the northern Tashkurgan fault, most thermochronologic data, which include biotite 40Ar/39Ar (Arbt), zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite (U-Th-Sm)/He (AHe) dates, record emplacement-related cooling, and only a few AHe dates possibly record exhumation of <2 km since ∼7 Ma ago. On the footwall of the southern Tashkurgan fault, almost all of the ZHe, AFT, and AHe dates record significant late Miocene to present exhumation; thus, we perform three-dimensional thermokinematic modeling for the normal slip along this fault segment. Modeling results indicate a probably constant slip rate on the southern Tashkurgan fault at a value of 1.4–1.5 mm/a, which corresponds to 6–7 km of both horizontal extension and footwall uplift since 6.5 Ma ago. All together, the geomorphic and thermochronologic evidences imply that the southern Tashkurgan fault is responsible for the ∼E–W extension along the southernmost portion of the Kongur Shan extensional system, while the northern fault segment plays a minor role in the extension. This result, combined with the previously published magnitude of extension along the southern Kongur Shan fault, indicates that the extension at any site along the southern Kongur Shan extensional system can be primarily attributed to normal faulting along a single border fault, which is a typical characteristic of an interbasin transfer zone with a transfer fault.

InSAR, Gravity, and Geomagnetic Observations Suggest the 2020 Mw 6.5 Stanley Earthquake Occurred on a Blind Strike-Slip and a Normal Fault

ABSTRACT The 2020 Mw 6.5 Stanley earthquake occurred in western North America and is the largest earthquake in Idaho state in the past ∼40 yr. The hypocenter is located at the western margin of the Centennial Tectonic Belt (CTB), which is a subprovince of the Basin and Range and characterized by a series of normal faults. In this study, the coseismic Interferometric Synthetic Aperture Radar observations, geophysical data, and aftershocks are jointly collected to estimate the seismogenic fault of the 2020 Stanley earthquake. The best-fitting fault models suggest the earthquake occurred on two blind faults. Slip on the main, west-dipping, seismogenic fault was sinistral and on the second fault predominantly normal slip with a minor component of right-lateral strike slip. Geophysical observations including gravity and geomagnetic data are consistent with the fault interpretations. The Coulomb failure stress (CFS) change indicates that the rupture of the main seismogenic fault had a positive triggering effect on the slip of the second fault and may have increased the rupture risk of the Sawtooth fault. Moreover, a potential seismic hazard risk zone with a notably low occurrence of aftershocks is found in the west of the central segment of the main seismogenic fault.

Variations in the present-day stress field and its implications for hydrocarbon development in the Hassi Terfa field, Hassi Messaoud, Algeria

Understanding the contemporary stress field and its variations is important in hydrocarbon production. These fluctuations are significant for borehole stability and trajectory, hydraulic stimulation, fault reactivation, and optimal well completion. In this study, we provide the first geomechanical model to determine the orientation and magnitude of the present-day stress of the Hassi Terfa field using geophysical logs to understand the origin of the spatial variation of the stress state. The breakouts from acoustic image logs provide an average maximum horizontal stress (SHmax) orientation of N115°, consistent with the Africa–Eurasia plate motion, which imposes the largest first-order stress source. However, our analysis demonstrates local stress perturbations near faults. This may mean that the stress field in the Hassi Terfa is superimposed by a third-order source of stress (<100 km). Our model demonstrates variations in stress magnitude with depth interpreted to be lithology-dependent, which act as a natural barrier against fracture propagation. We propose a new approach to quantify these perturbations via the stress regime index R′, using the magnitude of the principal stress components. The results demonstrate different layer-to-layer faulting regimes. These perturbations will limit the vertical propagation of hydraulic fracturing to the overlying formation, which enables it to access a larger reservoir volume and improve production. In general, a strike–slip regime with a slight normal slip component is interpreted for the study area. We develop the first-ever quantitative stress map using the relative principal stress magnitude parameter (Aϕ) to present the lateral variation of the stress regime throughout the Saharan platform. Results demonstrate a consistent strike–slip to normal/strike–slip regime with a uniform SHmax orientation. This map will help operators achieve optimal well direction and optimize hydraulic stimulation. Our results have considerable implications for hydrocarbon production in the central and southeastern Saharan platform.

Tectonic implications of the February 2023 Earthquakes (Mw7.7, 7.6 and 6.3) in south-eastern Türkiye

The series of earthquakes that took place on February 6, 2023 caused one of the saddest major calamities in Türkiye. The first major earthquake of magnitude Mw7.7 broke the Pazarcık and Erkenek segments moving north on the East Anatolian Fault Zone (EAFZ) between Türkoğlu and Çelikhan. According to the Coulomb failure criterion, the Pazarcık earthquake (Mw7.7) increased stress on the Sürgü-Çardak Fault, a segment on the north splay of the EAFZ, and nine hours later the Elbistan earthquake (Mw7.6) occurred. This great event ruptured the Çardak Fault, the western part of the E-W trending Sürgü-Çardak Fault between Nurhak and Göksun. The Amanos Fault, which extends from Türkoğlu south to Antakya, broke almost simultaneously to the first Pazarcık earthquake. Similarly, the earthquake that broke the Amanos Fault transferred increased stress to its south-western neighbour, the Cyprus-Antakya Transform Fault, triggering the 6.3 magnitude Samandağ earthquake 14 days later. The February 2023 earthquakes, which caused the collapse of >100,000 buildings and the death of >50,000 people, created surface ruptures hundreds of kilometres in length and caused different displacements on different faults, the two largest of which were 4.6 and 6.7 m. On all the faults where the deadly earthquakes occurred in February 2023, inversion of the focal mechanisms of the earthquakes (main shocks and their aftershocks) indicates a transtensional stress regime, or a change from strike-slip to normal slip. For all strike-slip inversions, the R values are <0.45 indicating transtension. The stress tensors obtained indicate left-lateral movement with normal component on all faults where the earthquakes occurred. The transtensional regime, which is thought to reflect regional tectonics, is the result of forces caused by relative movements of Arabia, eastern Mediterranean and Eurasia.

Optical and electrical dual-mode tactile sensor with interlinked interfaces recording normal force and slip for closed-loop robotics

The rapid development of electronic skin will allow disabled people and intelligent robots to interact more effectively with their surroundings. Nevertheless, it remains challenging to simultaneously capture multi-dimensional personalized information (including pressure and slip sensation) through simple device structure design with high stability under complex mechanical conditions. Here, a tactile sensor with simple structure and reliable performance (withstand considerable stretching, twisting, bending, and vibration) is designed for pressure and slip sensing. It is implemented by optical and electrical dual-mode sensing mechanisms and high toughness interlinked interface strategy (interfacial toughness ∼ 33.69 Jm−2, nearly 5 times higher than control sample). This device is composed of a periodic microstructured piezoresistive layer and a triboelectrification-induced electroluminescent (TIEL) layer, both of which are based on the quasi-homogeneous PDMS (polydimethylsiloxane) composite. The whole device possesses the characteristics of lightness, flexibility, and light-transmitting. Besides, the device could automatically locate and track the slip motion while detecting the normal pressure in a large range (0–––1,000 kPa). As an application demonstration, the sensor is installed on a flexible manipulator and combined with the closed-loop control system. Compared to a single electrical mode, the optical and electrical dual-mode tactile sensor could more accurately monitor the sliding of the clamped object, adjust the clamping force instantly, and avoid object slipping. The unique performance of the device shows great potential in trajectory recognition, artificial limbs, intelligent robots, and human–machine interfaces.

Fabric controls fault stability in serpentinite gouges

SUMMARY Serpentinites are polymineralic rocks distributed almost ubiquitously across the globe in active tectonic regions. Magnetite-rich serpentinites are found in the low-strain domains of serpentinite shear zones, which act as potential sites of nucleation of unstable slip. To assess the potential of earthquake nucleation in these materials, we investigate the link between mechanical properties and fabric of these rocks through a suite of laboratory shear experiments. Our experiments were done at room temperature and cover a range of normal stress and slip velocity from 25 to 100 MPa and 0.3 to 300 µm s−1, respectively. We show that magnetite-rich serpentinites are ideal materials since they display strong sensitivity to the loading rate and are susceptible to nucleation of unstable slip, especially at low forcing slip velocities. We also aim at the integration of mechanical and microstructural results to describe the underlying mechanisms that produce the macroscopic behaviour. We show that mineralogical composition and mineral structure dictates the coexistence of two deformation mechanisms leading to stable and unstable slip. The weakness of phyllosilicates allows for creep during the interseismic phase of the laboratory seismic cycle while favouring the restoration of a load-bearing granular framework, responsible of the nucleation of unstable events. During dynamic slip, fault zone shear fabric determines the mode of slip, producing either asymmetric or Gaussian slip time functions for either fast or slow events. We report rate/state friction parameters and integrate our mechanical data with microstructural observations to shed light on the mechanisms dictating the complexity of laboratory earthquakes. We show that mineralogical and fabric heterogeneities control fault slip behaviour.

Temporary stress regime reversal immediately after the complete release of the localized compressive stress by the 2021 Luxian Ms 6.0 earthquake, Sichuan Basin

Aftershocks can provide fundamental information of the seismogenic structure and the stress condition of the source region to reveal the seismogenic mechanism of earthquakes without clear surface rupture. On 16 September 2021, a destructive Ms 6.0 earthquake broke the seismic quiescence of the Luxian county in the inner Sichuan Basin, China. Here, we explore the seismogenic structure and the postseismic stress condition of the Luxian earthquake through characterizing sedimentary faults in the spatiotemporal distribution of aftershocks, through the focal mechanism solutions and further stress inversion, and through the coseismic rupture model based on synthetic aperture radar interferometry (InSAR) data. Our results show that aftershocks are concentrated at two clusters in the broad Yujiasi syncline. Seismicity of the northern cluster reveals that the main shock ruptured an east-southeast striking fault with a dip angle of ∼ 45° to the southwest (F0), and activated a gently dipping (∼ 18°) fault (F1) below F0 and a nearly vertical shallow fault (F2) on the northern side of F0. These three faults outline the edges of a thrust wedge in the sedimentary cover. The northern cluster occurred on a conjugate fault system within which steep faults with different dipping direction interlaced downward forming ‘V’ shapes. The main reverse rupture on the east-southeast striking F0 fault is inconsistent with the background northwest-southeast tectonic stress field. Combined with the morphology of anticlines, we suggest that the main shock was resulted from the localized NE-SW compressive stress concentration due to the inhomogeneous deformation of the sedimentary cover. Aftershocks with magnitude ≥ 2.0 are characterized by the dominant normal slip. Coulomb stress change (ΔCFS) results show that normal slip is enhanced by the main rupture. However, the amplitude of ΔCFS (a few bars) is not large enough to reverse the dominant slip direction of faults. Postseismic stress inversion results show a temporary stress regime reversal from the nearly north-south subhorizontal compressive stress regime before the main shock to the normal slip favored stress regime with a subvertical maximum principal stress (σ1). We suggest that the Luxian Ms 6.0 earthquake as an unusual event completely released the localized horizontal compressive stress and hence caused a temporary reversal of the localized stress regime.

Geothermal manifestations linkage with the Siulak Fault segment in Kerinci

Geothermal manifestation on the Sungai Medang and Semurup, Kerinci Regency appear along the Sumatran Fault System. Geological setting as well as this are interesting things to understand from the linkage between of them. To know this process, it is necessary to understand the fault structure mechanism and the presence geothermal features manifestations. The aim of this research in addition to understanding the linkage between of them, which comprehend the fault mechanism of the fault structure, so as to know the role of the fault structure in the appearance of geothermal features manifestation. Geothermal manifestation in Sungai Medang has geothermal features manifestation surface including hot spring, hot pool, geyser dome, hydrothermal alteration rock, sinter silica, and carbonate sinter. The fault structure measured and analysis on the eastern part of Siulak Fault segment of the Sungai Medang was found to be a normal right slip fault, but western part of Siulak Fault segment on the Semurup which strike-slip fault and normal right slip fault. The existence of geothermal features manifestation surface in fault zone of Siulak Fault segment is evidence that, the role of faults is as a controlled by apeear geothermal manifestation. The fault structure mechanism is the result of dextral movement of Siulak Fault which forms a pull-apart basin. This basin is single fault-bend basin as one master fault of active segment. The fault regime stress analysis obtained direction compressional force is trending north-northwestern and south-southeastern. This regime stress is locally stress on Sungai Penuh Basin.

Geodetic constraints of the 2015Mw6.5 Alor, East Indonesia earthquake: a strike-slip faulting in the convergent boundary

SUMMARYOn 2015 November 4, an Mw 6.5 earthquake struck the east region of Alor Island, eastern Indonesia. Here, we use Sentinel-1 and ALOS-2 data to explore the coseismic surface displacement of this earthquake. Based on the ALOS-2 coseismic interferograms, the first fault model and coseismic slip distribution of the 2015 Alor earthquake are presented in this study. The preferred slip model links to a blind south-southeast striking, south-southwest dipping strike-slip fault with amount of normal slip component and a peak slip of 2.09 m at 2.34 km of depth. Considering the fact that the ascending and descending InSAR prediction of the distributed slip model does not fit the InSAR observations at the northwest and southeast tips with the simple planar fault model. We tried to construct a strike-variable fault model to further improve data fit. The results of the calculated Coulomb stress change imply that the regions with positive CFS changes mainly located at the northwest and southeast extremities of the rupture of the Alor earthquake, and in the lobes north and south of the rupture. The most striking discovery from the InSAR observations of the Alor earthquake is that most of the displacements occurred on a fault whose existence was unknown before the earthquake.

Trapdoor Fault Activation: A Step Toward Caldera Collapse at Sierra Negra, Galápagos, Ecuador

AbstractThe 2018 Sierra Negra eruption resulted in meter‐scale subsidence due to basaltic magma extraction from a deflating reservoir. The eruption was also characterized by dike intrusions, &gt;4 MW earthquakes, and sulfur dioxide emissions. We use a combination of Interferometric Synthetic Aperture Radar, Digital Elevation Model, Global Positioning System and seismic data to assess conditions required to trigger episodic caldera collapse at Sierra Negra. The 2018 effusive eruption was mainly sourced from a horizontal sill located at ∼2 km depth, with a minimum erupted bulk volume of 0.19 km3. The modeled reservoir is bound by a C‐shaped ring of seismicity, suggesting trapdoor fault slip. Two &gt;4.5 MW earthquakes (5 and 22 July 2018) produced localized subsidence north of the southern trapdoor fault. After removing the modeled subsidence signal, distributed normal trapdoor fault slip explains the location of residual displacement. Furthermore, distributed fault models indicate slip occurred along the northern, central and southern segments of the trapdoor fault during the entire eruption, until 25 August 2018. Theoretical models of caldera collapse estimate that an erupted volume of 0.19 km3 is too small to trigger full‐scale caldera collapse, given the caldera aspect ratio (depth/diameter) of 0.22. Nonetheless, the spatial distribution and duration of seismicity and slip suggest trapdoor fault activation is the initial stage of caldera collapse at Sierra Negra, which may lead to full‐scale caldera collapse during larger eruptions. Alternatively, hundreds of medium‐sized eruptions, similar to that of 2018, may have triggered fault slip events over the past millennia.

Cenozoic slip along the southern Sierra Nevada normal fault, California (USA): A long-lived stable western boundary of the Basin and Range

AbstractThe uplift history of the Sierra Nevada, California, is a topic of long-standing disagreement with much of it centered on the timing and nature of slip along the range-bounding normal fault along the east flank of the southern Sierra Nevada. The history of normal fault slip is important for characterizing the uplift history of the Sierra Nevada, as well as for characterizing the geologic and geodynamic factors that drove, and continue to drive, normal faulting. To address these issues, we completed new structural studies and extensive apatite (U-Th)/He (AHe) thermochronometry on samples collected from three vertical transects in the footwall to the east-dipping southern Sierra Nevada normal fault (SNNF). Our structural studies on bedrock fault planes show that the SNNF is a steeply (~70°) east-dipping normal fault. The new AHe data reveal two elevation-invariant AHe age arrays, indicative of two distinct periods of cooling and exhumation, which we interpret as initiation of normal faulting along the SNNF at ca. 28–27 Ma with a second phase of normal faulting at ca. 17–13 Ma. We argue that beginning in the late Oligocene, the SNNF marked the now long-standing stable western limit, or breakaway zone, of the Basin and Range. Slip along SNNF, and the associated unloading of the footwall, likely resulted in two periods of uplift of Sierra Nevada during the late Cenozoic. Trench retreat, driven by westward motion of the North American plate, along the Farallon–North American subduction zone boundary, as well as the gravitationally unstable northern and southern Basin and Range pushing on the cold Sierra Nevada, likely drove the late Oligoceneaged normal slip along the SNNF and the similar-aged but generally local and minor extension within the Basin and Range. We posit that the thick proto–Basin and Range lithosphere was primed for late Oligocene extension by replacement of the steepening Farallon slab with hot and buoyant asthenosphere. While steepening of the Farallon slab had not yet reached the southern Sierra Nevada by late Oligocene time, we speculate that late Oligocene slip along the SNNF reactivated a late Cretaceous dextral shear zone as the Sierra Nevada block was pulled and pushed westward in response to trench retreat and gravitational potential energy. The dominant middle Miocene normal faultslip history along the SNNF is contemporaneous with high-magnitude slip recorded along range-bounding normal faults across the Basin and Range, including the east-adjacent Inyo and White mountains, indicating that this period of extension was a major regional tectonic event. We infer that a combination of slabdriven trench retreat along the Juan de Fuca–North America subduction zone boundary and clockwise rotation of the southern ancestral Cascade Range superimposed on continental lithosphere preconditioned for extension drove this episode of middle Miocene normal slip along the SNNF and extension to the east across the Basin and Range. Transtensional plate motion along the Pacific–North America plate boundary, and likely a growing slab window, continued to drive extension along the SNNF and the western Basin and Range, but not until ca. 11 Ma when the Mendocino triple junction reached the latitude of our northernmost (U-Th)/He transect.

Numerical and experimental study of the viscosity and mechanical parameters effect on tow feeding quality during automated fiber placement

For automated fiber placement (AFP), it is crucial to research the contact characteristics between tow and roller during the tow feeding process. However, it has not been widely explored. In this paper, a theoretical model of contact characteristics for the tow feeding process is established by analyzing the distribution of normal stress, tangential stress, adhesion zone, and slip zone, respectively. The model proposed a numerical algorithm for calculating the contact characteristic. Then the contact characteristic of the tow feeding system can be acquired and validated by the experiment and finite element method. The model that provides theoretical support for AFP optimization. Furthermore, proper pressure (P = 0.6Mpa) and tension (T = 3 N) for towpreg feeding under experimental conditions were obtained.

A novel dynamic dry friction model for applications in mechanical dynamical systems

This work presents a novel continuously differentiable, dynamic dry friction model, with dependence on normal contact force, slip velocity, and static and dynamic coefficients of friction. The state-of-the-art, Brown and McPhee friction model depends on transitional velocity, which is an empirical parameter. A limitation with this model is that there is no generic approach to select the optimal value for the transitional velocity for a certain application. The simulation results presented in this work highlight the sensitivity of friction force with transitional velocity in Brown and McPhee’s model to obtain smooth solutions, which are supportive in control system applications. It is because control systems require jitter-free signals in order to save costs on low-pass filters. The proposed model overcomes such empirical dependence on transition velocity through a combination of an iterative methodology and an empirical parameterization. In this article, a comprehensive analysis of the proposed friction model and the contributing parameters is carried out. The algorithm to implement the proposed friction model is elaborated. The proposed friction model is then simulated and compared against Brown and McPhee’s model. using a stick-slip benchmark problem. Furthermore, the proposed force model is applied to two spatial multibody systems formulated using index 0 tangent space differential-algebraic equations. The results demonstrate how the proposed friction model can be employed in dynamical mechanical systems. The independence on transitional velocity in the proposed friction model is observed to be effective for obtaining smooth solutions that make it suitable for control system applications.