Pn wave velocity and anisotropy underneath the central segment of the North-South Seismic Belt in China

We present a Pn wave velocity and anisotropy model of the central segment of the North-South Seismic Belt in China, where there are numerous stable basins and active faults, making this segment attractive for extensive studies. The model was obtained by a tomographic analysis of 49,973 Pn wave phase readings collected by the China Earthquake Networks Center and temporary stations in Yunnan and Sichuan. The tomographic velocity model shows that the average Pn wave velocity is 8.06km/s; prominent high-velocity (high-V) anomalies are visible under the Sichuan Basin, the Zoige Basin and the Ordos block, which clearly outline their tectonic mar- gins. A pronounced low-velocity (low-V) zone is observed from the Songpan-Ganzi block to the Chuan-Dian and Daliangshan blocks, suggesting the presence of hot material upwelling. The station delay data show a gradual variation from negative to positive values, possibly reflecting a crustal thickness variation from the southwest to the northeast of the study area. A correlation between the Pn wave anisotropy and the distribution of velocity anomalies is observed: anisotropy is relatively weaker in the high-V anomaly zones beneath stable basins, while it is stronger in the low-V anomaly zones and the high-to-low-V anomaly transition zones. The high-resolution velocity and anisotropy tomographic model that we obtained could also provide a better understanding of the study area seismicity, since the occurrence of strong earthquakes seems to be related to the presence and strength of lateral heterogeneities at the uppermost mantle level

Quantifying two-dimensional nonstationary signal with power-law correlations by detrended fluctuation analysis

In this paper, we develop a new method for the multifractal characterization of two-dimensional nonstationary signal, which is based on the detrended fluctuation analysis (DFA). By applying to two artificially generated signals of two-component ARFIMA process and binomial multifractal model, we show that the new method can reliably determine the multifractal scaling behavior of two-dimensional signal. We also illustrate the applications of this method in finance and physiology. The analyzing results exhibit that the two-dimensional signals under investigation are power-law correlations, and the electricity market consists of electricity price and trading volume is multifractal, while the two-dimensional EEG signal in sleep recorded for a single patient is weak multifractal. The new method based on the detrended fluctuation analysis may add diagnostic power to existing statistical methods

Hydrous melting driven upwelling from the mantle transition zone in the Mongolia plateau revealed by receiver function analysis

The detailed images of the mantle transition zone (MTZ) give insights into the nature of mantle upwelling from the deep Earth. We use receiver function to investigate the MTZ structure beneath the Mongolia Plateau using earthquakes recorded by 223 stations deployed in the Central Asian Orogenic Belt. The topographies of the 410 km (D410) and 660 km (D660) discontinuities are both characterized by slight depressions in most parts of the Mongolia Plateau. An obvious low-velocity layer (LVL) atop the MTZ with an average thickness of ∼40 km is observed beneath this study area, indicating the hydrous partial molten layer atop the D410 and a hydrous MTZ. The D410 depth of ∼410 km and the LVL up to ∼60 km thick beneath the Dariganga volcano imply that there is a chemically distinct hydrous upwelling related to the subducted Pacific slab rather than a classic thermal-dominated upwelling. The ∼10 km thinned MTZs are found beneath the western Hangay Dome and the Middle Gobi volcano. A narrow NS-trending MTZ thickening zone extending from the Hovsgol rift to the central Hangay Dome is mainly caused by a ∼10 km depression of D660. We speculate that the mantle upwelling beneath the Hangay Dome may be related to the stagnant slab descending through the MTZ, rather than being rooted from the deep lower mantle. Hydrous melting-driven upwellings from the MTZ beneath the Mongolia Plateau play a key role in intraplate volcanism.Published versionThis work is supported by National Natural Science Foundation of China (42030310, 42074102) and research grants from National Institute of Natural Hazards, Ministry of Emergency Manage-ment of China (Grant ZDJ2020-11)

Spatial–Temporal Variations, Ecological Risk Assessment, and Source Identification of Heavy Metals in the Sediments of a Shallow Eutrophic Lake, China

The contamination of heavy metals (Pb, Cr, Hg, Cd, Ni, Cu, Zn, As, and Sb) in the sediments were investigated in Lake Yangcheng, a eutrophic lake in China. Results showed that the average concentrations of each metal in the surface sediments generally exceeded their corresponding background values. Higher values were observed in deeper zones, supporting the retention and accumulation of heavy metals in the core sediments. The spatial distributions of metal averages, pollution load index (PLI), and combined ecological risk index (RI) revealed that ecological risks were highest in the west lake, followed by middle lake, and were lowest in the east section. For the temporal variations of metal contents, the highest concentration was usually observed in the winter. However, the seasonal dynamics of Hg showed a different pattern with higher values in the autumn and lower values in the winter. According to contamination factor (CF), the Hg and Sb contaminations were considerable, while the other metals were moderate contamination. In terms of geoaccumulation index (Igeo) values, sediments were moderately–heavily polluted by Sb and moderately polluted by Hg, Cd, and Ni. Meanwhile, Hg exhibited a considerable health risk, while Cd and Sb were moderate risks, based on single ecological risk index (Er) values. Significant positive correlations among heavy metals and principal component analysis (PCA) indicated that anthropogenic activities were major sources. The source of Sb might be different from other metals, with industrial discharge as the main loading. This study highlighted the urgency of taking measures to prevent Hg, Sb, and Cd pollutions in Lake Yangcheng, especially the west region of this lake

High Methanol Gas-Sensing Performance of Sm2O3/ZnO/SmFeO3 Microspheres Synthesized Via a Hydrothermal Method

Abstract In this work, we synthesized Sm2O3/ZnO/SmFeO3 microspheres by a hydrothermal method combined with microwave assistance to serve as a methanol gas sensor. We investigated the effect on the microstructure at different hydrothermal times (12 h, 18 h, 24 h, and 30 h), and the BET and XPS results revealed that the specific surface area and adsorbed oxygen species were consistent with a microstructure that significantly influences the sensing performance. The gas properties of the Sm2O3-doped ZnO/SmFeO3 microspheres were also investigated. With a hydrothermal time of 24 h, the gas sensor exhibited excellent sensing performance for methanol gas. For 5 ppm of methanol gas at 195 °C, the response reached 119.8 with excellent repeatability and long-term stability in a 30-day test in a relatively high humidity atmosphere (55–75% RH). Even at 1 ppm of methanol gas, the response was also higher than 20. Thus, the Sm2O3-doped ZnO/SmFeO3 microspheres can be considered as prospective materials for methanol gas sensors