Curved orogenic belts, back-arc basins, and obduction as consequences of collision at irregular continental margins

Continental collisions commonly involve highly curved passive plate margins, leading to diachronous continental subduction during trench rollback. Such systems may feature back-arc extension and ophiolite obduction postdating initial collision. Modern examples include the Alboran and Banda arcs. Ancient systems include the Newfoundland and Norwegian Caledonides. While external forces or preexisting weaknesses are often invoked, we suggest that ophiolite obduction can equally be caused by internal stress buildup during collision. Here, we modeled collision with an irregular subducting continental margin in three-dimensional (3-D) thermo-mechanical models and used the generated stress field evolution to understand resulting geologic processes. Results show how tensional stresses are localized in the overriding plate during the diachronous onset of collision. These stresses thin the overriding plate and may open a back-arc spreading center. Collision along the entire trench follows rapidly, with inversion of this spreading center, ophiolite obduction, and compression in the overriding plate. The models show how subduction of an irregular continental margin can form a highly curved orogenic belt. With this mechanism, obduction of back-arc oceanic lithosphere naturally evolves from a given initial margin geometry during continental collision.

Hydrothermal anomalies of the Earth's surface and crustal seismicity related to Ms8.0 Wenchuan EQ

Hydrothermal anomalies related to the Ms8.0 Wenchuan earthquake (EQ) on May 12, 2009, have been widely reported. However, the reported anomalies have not been associated with multi-geosphere analysis, and space–time analysis with crustal seismicity is lacking. In this paper, the space–time variation of hydrothermal parameters, including soil moisture, soil temperature, near-surface relative humidity (RHsig995) and air temperature (TMPsfc), was first extracted and analyzed with the NCEP-FNL reanalysis dataset. The b-value (a seismic parameter from the Gutenberg–Richter law) was calculated and mapped to unravel the crustal stress and rock rupture. Our results reveal a similar time window for hydrothermal anomalies on April 20 and April 30, 2008, and these anomalies are mainly distributed along the southern and middle parts of the Longmenshan fault zone. The surface temperature anomalies lag behind the humidity anomalies, and the accelerating stress accumulation started since June 2007 and lasted for eight to nine months before the mainshock. The b-value mapping shows a segmented difference along strike of the Longmenshan fault, and that regional stress accumulated mainly in the southern parts of the F2 and F3 faults. We propose the occurrence of a complex coupling process led by crustal stress buildup before the Wenchuan EQ. The anomalies are concentrated in the southern part of the surface rupture zone. The prolonged crustal stress accumulation corresponds to the short intermittent hydrothermal response on the Earth’s surface before the Wenchuan EQ. Our findings reveal new hydrothermal anomalies in the Earth’s surface and atmosphere and explore direct link with seismogenic processes in the crust.

Effects of Curing-Induced Residual Stress on Composite Strength

An integrated processing-damage model was developed to predict the inter-lamina strength of a plain weave composite flange manufactured using the Resin Transfer Molding (RTM) technique. The plain weave composite flange was subjected to four-point bending test to characterize its inter-lamina strength. A Representative Volume Element (RVE) at the fiber–matrix level was established to study the effect of curing-induced residual stress on the resulting composite strength. In order to calculate the residual stress, the curing cycle of the experiment was imposed on the RVE. After fully cured, the RVE was virtually loaded and the cohesive element and Smeared Crack Approach (SCA) were employed to capture the fiber-matrix debonding and matrix cracking responses, respectively. Due to the nature of stress history dependency, the SCA was formulated in the incremental form to reflect the stress buildup. The result shows that both fiber-matrix debonding and matrix cracking can be captured during the virtual loading. However, the load drop in the simulation mainly depends the matrix cracking. As the stress buildup in the matrix is dramatic, it demonstrates that the residual stress has large impact on the composite inter-lamina strength. The numerical methods in this paper can be used as an efficient tool in optimizing the curing process of composite material.

Stress Buildup Upon Crystallization of GeTe Thin Films: Curvature Measurements and Modelling

Phase change materials are attractive materials for non-volatile memories because of their ability to switch reversibly between an amorphous and a crystal phase. The volume change upon crystallization induces mechanical stress that needs to be understood and controlled. In this work, we monitor stress evolution during crystallization in thin GeTe films capped with SiOx, using optical curvature measurements. A 150 MPa tensile stress buildup is measured when the 100 nm thick film crystallizes. Stress evolution is a result of viscosity increase with time and a tentative model is proposed that renders qualitatively the observed features.

Using rigid microplate motions to detect the stress buildup preceding large earthquakes: a feasibility test based on synthetic models

<p>Assessing the temporal evolution of stresses along seismogenic faults is typically done by combining geodetic observations collected near the locations of previous large earthquakes with modeling of the interseismic, coseismic, and postseismic deformation. Here we explore whether it is feasible to link the charge phase of large earthquakes to rigid microplate motions, which can be inferred from geodetic observations that are instead collected further away from crustal faults. We use numerical simulations of the dynamics and associated kinematics of an idealized, rigid microplate subject to stress buildups and drop-offs from a series of earthquakes. Simulations span the charging cycle of a single 6.5 < M<sub>W</sub> < 8 earthquake. Several M<sub>W</sub> < 6.5 earthquakes distributed according to the Gutenberg-Richter law occur meanwhile. We use large ensembles of simulations featuring randomly-generated earthquake hypocenters and make statistical assessments of the fraction of model time needed for the microplate motions to depart from the initial one to a degree that is larger than typical geodetic uncertainties, and for at least 90% of the remaining time before the large earthquake occurs. We find such a fraction (i) to be only one tenth in simulations that do feature a large earthquake, (ii) to be longer in simulations that do not, and (iii) to remain small for realistic microplate geometries and asthenosphere viscosity/thickness values. Our inferences hold also when we simulate geodetic time series shorter than the large-earthquake cycle, and even when we assume that only half of the stress buildup affects the microplate rigid motion.</p>

A Resonant Pressure Microsensor Based on Double-Ended Tuning Fork and Electrostatic Excitation/Piezoresistive Detection

This paper presents a resonant pressure microsensor relying on electrostatic excitation and piezoresistive detection where two double-ended tuning forks were used as resonators, enabling differential outputs. Pressure under measurement caused the deformation of the pressure sensitive membrane, leading to stress buildup of the resonator under electrostatic excitation with a corresponding shift of the resonant frequency detected piezoresistively. The proposed microsensor was fabricated by simplified SOI-MEMS technologies and characterized by both open-loop and closed-loop circuits, producing a quality factor higher than 10,000, a sensitivity of 79.44 Hz/kPa and an accuracy rate of over 0.01% F.S. In comparison to the previously reported resonant piezoresistive sensors, the proposed device used single-crystal silicon as piezoresistors, which was featured with low DC biased voltages, simple sensing structures and fabrication steps. In addition, the two double-ended tuning forks were used as resonators, producing high quality factors and differential outputs, which further improved the sensor performances.