Atomistic processes of surface-diffusion-induced abnormal softening in nanoscale metallic crystals

Ultrahigh surface-to-volume ratio in nanoscale materials, could dramatically facilitate mass transport, leading to surface-mediated diffusion similar to Coble-type creep in polycrystalline materials. Unfortunately, the Coble creep is just a conceptual model, and the associated physical mechanisms of mass transport have never been revealed at atomic scale. Akin to the ambiguities in Coble creep, atomic surface diffusion in nanoscale crystals remains largely unclear, especially when mediating yielding and plastic flow. Here, by using in situ nanomechanical testing under high-resolution transmission electron microscope, we find that the diffusion-assisted dislocation nucleation induces the transition from a normal to an inverse Hall-Petch-like relation of the strength-size dependence and the surface-creep leads to the abnormal softening in flow stress with the reduction in size of nanoscale silver, contrary to the classical “alternating dislocation starvation” behavior in nanoscale platinum. This work provides insights into the atomic-scale mechanisms of diffusion-mediated deformation in nanoscale materials, and impact on the design for ultrasmall-sized nanomechanical devices.

Interseismic Slip and Coupling along the Haiyuan Fault Zone Constrained by InSAR and GPS Measurements

The Haiyuan fault zone is an important tectonic boundary and strong seismic activity belt in northeastern Tibet, but no major earthquake has occurred in the past ∼100 years, since the Haiyuan M8.5 event in 1920. The current state of strain accumulation and seismic potential along the fault zone have attracted significant attention. In this study, we obtained the interseismic deformation field along the Haiyuan fault zone using Envisat/ASAR data in the period 2003–2010, and inverted fault kinematic parameters including the long-term slip rate, locking degree and slip deficit distribution based on InSAR and GPS individually and jointly. The results show that there is near-surface creep in the Laohushan segment of about 19 km. The locking degree changes significantly along the strike with the western part reaching 17 km and the eastern part of 3–7 km. The long-term slip rate gradually decreases from west 4.7 mm/yr to east 2.0 mm/yr. As such, there is large strain accumulation along the western part of the fault and shallow creep along the Laohushan segment; while in the eastern section, the degree of strain accumulation is low, which suggests the rupture segments of the 1920 earthquake may have been not completely relocked.

Deciphering the evolution of the Bleis Marscha rock glacier (Val d'Err, eastern Switzerland) with cosmogenic nuclide exposure dating, aerial image correlation, and finite-element modelling

We constrain the Holocene morphodynamic development of the Bleis Marscha rock glacier (Err-Julier area, eastern Swiss Alps) with fifteen cosmogenic nuclide exposure ages (10Be, 36Cl), 2003/2012 horizontal surface creep rate quantification from orthophoto orientation correlation, and semi-quantitative ice-content estimates from finite-element modelling. The results suggest that the complex Bleis Marscha rock glacier formed during two activity phases, one in the early Holocene and one in the late Holocene, separated by a mid-Holocene period of inactivation. The now transitional-inactive low-elevation lobes (first generation) formed after the retreat of the Egesen cirque glacier in a pulse-like manner at 11.5–9.0 ka. Rock-glacier viscosities inverted with the finite-element model hint at ground ice in these lobes which is possibly as old as its early-Holocene debris cover. In contrast to the debris-conditioned rapid emplacement, the thermally controlled permafrost degradation is still ongoing, likely attenuated by thermal decoupling from the insulating coarse-debris boulder mantle. Nuclide loss from boulder erosion, affecting the nuclide inventory of boulders independently, led to a heterogeneous exposure age distribution on the transitional-inactive lobes. Exposure ages on such disturbed lobes record time elapsed since inactivation and are interpreted as (minimum) stabilisation ages. The inception of the active high-elevation lobes (second generation) at 2.8 ka is related to the late-Holocene cooling recorded at numerous sites across the Alps. Precise exposure ages of the last 1.2 ka correlate with down-stream distance and yield a long-term average surface speed coincident with 2003/2012 measurements. These long-term consistent surface creep rates indicate stable permafrost conditions and continuous rock-glacier growth despite the intermittent late-Holocene glacier cover of the Bleis Marscha cirque. The exposure ages on active, undisturbed lobes record time elapsed since boulder emergence at the rock-glacier root and are interpreted as travel time estimates. This work contributes to deciphering the past to quasi-present climate sensitivity of rock glaciers.

Spatio-temporal variations of surface creep along the Hazar-Palu Segment of the East Anatolian Fault, Turkey

<p>Aseismic creep is detected and started to be monitored along the 100 km-long Palu-Hazar Segment of the Eastern Anatolian Fault (EAF) in Turkey, a major plate boundary between Anatolia and Arabia. We used creepmeters, InSAR, GPS, and seismic observations to document the extent and magnitude of this motion in order to increase our knowledge on the spatiotemporal variation of creep along the EAF, its relationship with the lithology and tectonic structures, and the stress change on the neighboring fault segments. Until now, we observed the region with continuous GPS and survey GPS measurements with near (~ 0.1- 4 km to the fault) and far-field (~25 – 225 km from the fault) stations to determine the depth of the creep zone and its velocity along the EAF. We processed 6 years (2014 – 2019) of continuous and 7 campaign (2015 – 2019) GPS data with GAMIT/GLOBK software. With elastic models, we determined a creep rate that reaches about 5 ± 0.3 mm/yr from GPS observations (50% of secular velocity). In addition to surface control of the creeping zone, we analyzed the deformations, by using three Terrestrial Laser Scanner (TLS) survey, in the Palu railway tunnel that crosses the fault where the walls of the tunnel have been offset by 15 ± 2 mm since the construction in the middle of the last century. Also, two creepmeters were installed inside the tunnel and transient creep anomalies are detected. These results are correlated with seismic and InSAR data (This study is supported by TUBITAK 1001 projects 114Y250 and 118Y450).</p><p>Keywords: Hazar-Palu, Creep, East Anatolian Fault, Earthquake, GPS, InSAR, TLS</p>

Surface creep rate distribution along the Philippine fault, Leyte Island, and possible repeating of Mw ~ 6.5 earthquakes on an isolated locked patch

Active faults commonly repeat cycles of sudden rupture and subsequent silence of hundreds to tens of thousands of years, but some parts of mature faults exhibit continuous creep accompanied by many small earthquakes. Discovery and detailed examination of creeping faults on land have been in a rapid progress with the advent of space-borne synthetic aperture radar interferometry. In this study, we measured the spatial variation of the creep rate along the Philippine fault on Leyte Island using ALOS/PALSAR data acquired between October 2006 and January 2011. Prominent creep of $$33\pm {11}$$33±11 mm/year was estimated in northern and central parts of the island except for a locked portion around latitude 11.08–11.20$$^\circ$$∘ N. We compared the creep rate distribution along the fault with the slip distribution of the 2017 $$M_w$$Mw 6.5 Ormoc earthquake which occurred in northern Leyte, estimated from the displacements mapped by ALOS-2/PALSAR-2 interferometric data. The estimated slip of the 2017 earthquake amounted up to 2.5 m and to moment magnitude of 6.49, with the dominant rupture area coinciding with the locked portion identified from the interseismic coupling analysis. Teleseismic waveforms of the 2017 earthquake and another event that occurred in 1947 ($$M_s$$Ms 6.9) exhibit close resemblance, indicating two ruptures of rather similar locations and magnitudes with a time interval of 70 years.

Sub-surface mechanical properties and sub-surface creep behavior of wood-plastic composites reinforced by organoclay

Wood-plastic composites (WPC) were manufactured from polypropylene, wood flour, maleic anhydride grafted polypropylene and organoclay. The sub-surface mechanical properties and the sub-surface creep behavior of the organoclay-based WPC were examined by the nanoindentation technique. The results showed that the hardness, elastic modulus and creep resistance of the WPC enhanced with the loading of C20 organoclay. This enhancement was subject to the organoclay content and the dispersion of organoclay in the polymer matrix. The hardness, elastic modulus and creep resistance of WPC with 1 wt% organoclay content enhanced by approximately 36%, 41% and 17%, respectively, in contrast with WPC without organoclay. To study the impact of organoclay content on the creep performance of WPC, a viscoelastic model was actualized. The results demonstrated that the model was in good agreement with the experimental information. Reinforcement of organoclay prompts expansion in elastic deformation and instigates a higher initial displacement at the early stage of creep.