Three-dimensional variations of the slab geometry correlate with earthquake distributions at the Cascadia subduction system

Significant along-strike variations of seismicity are observed at subduction zones, which are strongly influenced by physical properties of the plate interface and rheology of the crust and mantle lithosphere. However, the role of the oceanic side of the plate boundary on seismicity is poorly understood due to the lack of offshore instrumentations. Here tomographic results of the Cascadia subduction system, resolved with full-wave ambient noise simulation and inversion by integrating dense offshore and onshore seismic datasets, show significant variations of the oceanic lithosphere along strike and down dip from spreading centers to subduction. In central Cascadia, where seismicity is sparse, the slab is imaged as a large-scale low-velocity feature near the trench, which is attributed to a highly hydrated and strained oceanic lithosphere underlain by a layer of melts or fluids. The strong correlation suggests that the properties of the incoming oceanic plate play a significant role on seismicity

Validation of Shear‐Wave Velocity Models of the Pacific Northwest

Four surface‐wave tomographic models in the Pacific Northwest and a combined CRUST2.0 and AK135 model are tested and validated systematically. Synthetic Green’s functions calculated with the models using a finite‐difference method are compared with empirical Green’s functions at periods of 7–50 s. To ensure high‐quality signals, empirical Green’s functions are extracted from the ambient noise cross correlation of vertical‐to‐vertical components between station pairs that have up to a decade of recorded data. The observed and synthetic Green’s functions are cross correlated at multiple frequency bands to determine phase delay times and cross‐correlation coefficients. The delay time predicted by the CRUST2.0 and AK135 model is predominantly positive and is linearly dependent on interstation distance, indicating that the combined model is, on average, too fast for the Pacific Northwest. Among the four shear‐wave velocity models, CUB and one model derived from regional tomography exhibit moderately and weakly negative linear trends, respectively, between the delay time and interstation distance, a result indicative of a slower‐than‐actual velocity. The delay times of the other two models are normally distributed with an approximately zero mean and without any apparent relationship with interstation distance. The cross‐correlation coefficients are more scattered at short periods, reflecting unresolved heterogeneities of the crust structure in these models. The misfit between the empirical Green’s functions and synthetic waveforms suggests the need for a better‐resolved crust and uppermost mantle velocity model, which is critical for the precise estimate of ground motion for seismic hazard evaluation and understanding of the tectonic processes of the Pacific Northwest

Upper Mantle Structure of the Cascades from Full-Wave Ambient Noise Tomography: Evidence for 3D Mantle Upwelling in the Back-Arc

Melt generation and volcanism at subduction zones may result from several possible processes: hydration of the mantle wedge by fluid released from the slab, subduction-induced mantle upwelling beneath the back-arc, and heating of downgoing sediments/oceanic crust atop the slab. Each process predicts a distinctly different spatial pattern of melt generation and can thus be distinguished with high-resolution seismic imaging. Here we construct an upper mantle model of the Pacific Northwest using a full-wave ambient noise tomographic method. Normalized vertical components of continuous seismic records at station pairs are cross-correlated to extract empirical Green\u27s functions at periods of 7–200 s. We simulate wave propagation within the 3D Earth structure using a finite-difference method and calculate sensitivity kernels of Rayleigh waves to perturbations of VpVp and VsVs based on the Strain Green\u27s Tensor database. Phase delays are extracted by cross-correlating the observed and synthetic waveforms at multiple frequency bands. Our tomographic result reveals three separate low shear-wave velocity anomalies along the back-arc in the upper mantle ∼200 km east of the Cascade volcanic arc, with the central one being the largest in size and lowest in velocity. These back-arc low-velocity anomalies are spatially correlated with the three arc-volcano clusters. The geometry of the low-velocity volumes relative to the slab and arc is consistent with the pattern of subduction-induced decompressional melting in the back-arc. Their along-strike variation suggests that the large-scale plate-motion-induced flow in the back-arc mantle wedge is modulated by small-scale convection, resulting in a highly 3D process that defines the segmentation of volcanism along the Cascade arc

A Preliminary Full‐Wave Ambient‐Noise Tomography Model Spanning from the Juan de Fuca and Gorda Spreading Centers to the Cascadia Volcanic Arc

The Cascadia Initiative (CI) Amphibious Array provides us an unprecedented opportunity to investigate seismologically the formation, alteration, and subduction of the downgoing Juan de Fuca and Gorda plates, as well as the fore‐arc and volcanic arc (Fig. 1). Formed at the spreading center, the oceanic crust undergoes normal faulting near the ridge axis. As the plate cools and moves away from the spreading center, the thermal stress and forces at the plate boundaries and the base of the plate may cause faulting and deformation in the plate interior. Near the subduction trench, the plate bends, forming cracks in the upper plate (e.g., Ranero et al., 2003). The faults and cracks provide pathways for fluid to penetrate deep into the crust and possibly mantle lithosphere (e.g., Nedimović et al., 2009), causing chemical reactions that alter the composition of the plate, including serpentinization of the mantle lithosphere (Melson and Thompson, 1971). As the plate subducts, fluid within the plate and in the entrained sediment is released progressively with increasing pressure and temperature, affecting the rheology and fault behavior at and near the plate interface and resulting in partial melting in the mantle wedge and volcanism along the arc (Ranero et al., 2003). To understand subduction zones, we must have a clear and complete picture of the fore‐arc structure and the incoming plate at the trench, which in turn requires a good understanding of the interior of the plate

Transformation of worst weed into N-, S-, and P-tridoped carbon nanorings as metal-free electrocatalysts for the oxygen reduction reaction

Substituting sustainable/cost-effective catalysts for scarce and costly metal ones is currently among the major targets of sustainable chemistry. Herein we report the synthesis of N-, S-, and P-tridoped, worst-weed-derived carbon nanorings (WWCNRs) that can serve as metal-free and selective electrocatalyst for the oxygen reduction reaction (ORR). The WWCNRs are synthesized via activation-free polymerization of worst weed, Eclipta prostrate, and then removal of the metallic residues by HCl. The WWCNRs exhibit good catalytic activity towards the 4 electron-transfer ORR with low onset potential and high kinetic limiting current density, along with high selectivity (introducing CO, the sample loses onl

Improved multiple feature-electrochemical thermal coupling modeling of lithium-ion batteries at low-temperature with real-time coefficient correction.

Monitoring various internal parameters plays a core role in ensuring the safety of lithium-ion batteries in power supply applications. It also influences the sustainability effect and online state of charge prediction. An improved multiple feature-electrochemical thermal coupling modeling method is proposed considering low-temperature performance degradation for the complete characteristic expression of multi-dimensional information. This is to obtain the parameter influence mechanism with a multi-variable coupling relationship. An optimized decoupled deviation strategy is constructed for accurate state of charge prediction with real-time correction of time-varying current and temperature effects. The innovative decoupling method is combined with the functional relationships of state of charge and open-circuit voltage to capture energy management effectively. Then, an adaptive equivalent-prediction model is constructed using the state-space equation and iterative feedback correction, making the proposed model adaptive to fractional calculation. The maximum state of charge estimation errors of the proposed method are 4.57% and 0.223% under the Beijing bus dynamic stress test and dynamic stress test conditions, respectively. The improved multiple feature-electrochemical thermal coupling modeling realizes the effective correction of the current and temperature variations with noise influencing coefficient, and provides an efficient state of charge prediction method adaptive to complex conditions

Sharp Bounds for the General Sum-Connectivity Indices of Transformation Graphs

Given a graph G, the general sum-connectivity index is defined as χα(G)=∑uv∈E(G)dGu+dGvα, where dG(u) (or dG(v)) denotes the degree of vertex u (or v) in the graph G and α is a real number. In this paper, we obtain the sharp bounds for general sum-connectivity indices of several graph transformations, including the semitotal-point graph, semitotal-line graph, total graph, and eight distinct transformation graphs Guvw, where u,v,w∈+,-

Steering angle sensorless control for four-wheel steering vehicle via sliding mode control method

This paper presents a new sensorless control method for four-wheel steering vehicles. Compared to the existing sensor-based control, this approach improved dynamic stability, manoeuvrability, and robustness in case of malfunction of the front steering angle sensor. It also provided a software redundancy and backup solution, as well as improved fault tolerance. The strategy of the sensorless control is based on the sliding mode method to estimate the replacement of the front steering input from the errors between the vehicle’s measured and desired values of the vehicle’s sideslip angle and yaw rate. The simulation results demonstrate that the observer effectively estimated the front-wheel steering angle at both low and high speeds scenarios in the cornering and lane change manoeuvres. Furthermore, the sensorless control approach can achieve equivalent control performances to the sensor-based controller including a small and stable yaw rate response and zero sideslip angle. The results of the study offer a potential solution for improving manoeuvrability, stability, and sensor fault tolerance of four-wheel steering vehicles

A fluorescent bisboronic acid compound that selectively labels cells expressing oligosaccharide Lewis X

Two fluorescent diboronic acid compounds (6a and 6b) with a dipeptide linker were synthesized as potential sensors for cell surface saccharide Lewis X (Le(X)). Compound 6a with a dipeptide (H-Asp-Ala-) as the linker was found to selectively label CHOFUT4 cells, which express Le(x), at micromolar concentrations, while non-Le(x)-expressing control cells were not labeled

Demographics will reverse three multi-decade global trends

Between the 1980s and the 2000s, the largest ever positive labour supply shock occurred, resulting from demographic trends and from the inclusion of China and eastern Europe into the World Trade Organization. This led to a shift in manufacturing to Asia, especially China; a stagnation in real wages; a collapse in the power of private sector trade unions; increasing inequality within countries, but less inequality between countries; deflationary pressures; and falling interest rates. This shock is now reversing. As the world ages, real interest rates will rise, inflation and wage growth will pick up and inequality will fall. What is the biggest challenge to our thesis? The hardest prior trend to reverse will be that of low interest rates, which have resulted in a huge and persistent debt overhang, apart from some deleveraging in advanced economy banks. Future problems may now intensify as the demographic structure worsens, growth slows, and there is little stomach for major inflation. Are we in a trap where the debt overhang enforces continuing low interest rates, and those low interest rates encourage yet more debt finance? There is no silver bullet, but we recommend policy measures to switch from debt to equity finance