Azimuthal anisotropy retrieved from surface waves is important for constraining depthvarying deformation patterns in the crust and upper mantle. We present a direct inversion technique for the three-dimensional shear wave speed azimuthal anisotropy based on mixed-path surface wave traveltime data. This new method includes two steps: (1) inversion for the 3-D isotropic Vsv model directly from Rayleigh wave traveltimes and (2) joint inversion for both 3-D Vsv azimuthal anisotropy and additional 3-D isotropic Vsv perturbation. The joint inversion can significantly mitigate the trade-off between strong heterogeneity and anisotropy. With frequency-dependent ray tracing based on 2-D isotropic phase speed maps, the new method takes into account the ray-bending effect on surface wave propagation. We apply the new method to a regional array in Yunnan, southwestern China. Using Rayleigh wave phase velocity dispersion data in the period band of 5-40 s extracted from ambient noise interferometry, we obtain a 3-D model of shear wave speed and azimuthal anisotropy in the crust and uppermost mantle in Yunnan. This model reveals that two midcrust low-velocity zones are possible weak channels, and the azimuthal anisotropy at a depth of 5 to 30 km is mainly controlled by nearby strike-slip faults, some of which also approximately coincide with the lateral boundaries of the crustal low-velocity zones. Approximately south of 26°N, the upper crustal azimuthal anisotropy from our model is significantly different from the upper mantle anisotropy inferred by shear wave splitting, indicating different deformation styles between the crust and upper mantle in southern Yunnan.
Several models have been proposed to describe the tectonic evolution of SE Tibet and its marginal areas. Hence, high-resolution crustal velocity models are essential to address this controversy. With waveform data from 73 broadband stations in southwest China and northern Vietnam, we invert for a 3-D shear wave velocity model of the crust and uppermost mantle from ambient noise tomography. Our model reveals that the midlower crustal low-velocity zone in the Xiaojiang Fault Zone extends farther southward across the Red River Fault to Vietnam and is approximately bounded by the Xiaojiang and Dien Bien Phu faults to the east. We suggest that the observed low-velocity zone represents a mechanically weak zone in the mid-lower crust, which may serve as a channel for efficient southward material transport in SE Tibet. With our results and previous evidence, we propose a combined model that integrates rigid block extrusion and crustal channel flow to describe the large-scale material transport in SE Tibet. We further propose a two-phase material transport model in SE Tibet after the India-Eurasia plate collision: (1) rigid block extrusion between the right-lateral Sagaing Fault and left-lateral Red River Fault during the early Oligocene-early Miocene and (2) a combined model of rigid block extrusion and material channel flow in the mid-lower crust from the late Miocene to the present. The southward crustal material transport is likely to be diverted along two major channels around the more rigid crust beneath the inner zone of the Emeishan large igneous province.
Chemodynamic therapy (CDT) utilizes Fenton or Fenton‐like reactions to convert hydrogen peroxide (H2O2) into cytotoxic hydroxyl radicals (•OH) and draws extensive interest in tumor therapy. Nevertheless, high concentrations of glutathione (GSH) and insufficient endogenous H2O2 often cause unsatisfactory therapeutic efficacy. Herein, a GSH‐depleting and H2O2 self‐providing carrier‐free nanomedicine that can efficiently load indocyanine green (ICG), β‐lapachone (LAP), and copper ion (Cu2+) (ICG‐Cu2+‐LAP, LICN) to mediate synergetic photothermal and chemotherapy in enhanced chemodynamic therapy is designed. The results show that LICNs successfully enter tumors owing to the enhanced permeability and retention effect. Through the reductive intracellular environment, Cu2+ in LICN can react with intracellular GSH, alleviate the antioxidant capacity of tumor tissues, and trigger the release of drugs. When LICN is subjected to near‐infrared (NIR) irradiation, enhanced photothermal effect and upregulated expression of NAD(P)H quinone oxidoreductase‐1 (NQO1) are observed. Meanwhile, the released LAP not only supports chemotherapy but also catalyzes NQO1 and produces sufficient endogenous H2O2, thereby increasing the efficiency of Cu+‐based Fenton‐like reaction. Notably, GSH depletion and H2O2 self‐sufficiency generate sufficient •OH and kill tumor cells with high specificity. Overall, the study provides an innovative strategy to self‐regulate GSH and H2O2 levels for effective anticancer therapy.
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