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The Sichuan-Yunnan area is located at the southeastern margin of the Tibetan Plateau, where tectonic movement is strong with deep and large faults distributed in a staggered manner, which results in strong seismic activities and severe earthquake hazards. Since the 21st century, several earthquakes of magnitude 7.0 or above occurred in this region, which have caused huge casualties and economic losses, especially the 2008 Ms8.0 Wenchuan earthquake. At present, earthquake monitoring and source parameter inversion, strong earthquake hazard analysis and disaster assessment are still the focus of seismological researches in the Sichuan-Yunnan region. Regional high-precision 3D community velocity models are fundamental for these studies. In this paper, by assembling seismic observations at permanent seismic stations and several temporary dense seismic arrays in this region, we obtained about 7.06 million body wave travel time data (including absolute and differential travel times) using a newly developed artificial intelligence body wave arrival time picking method and about 100,000 Rayleigh wave phase velocity dispersion data in the period range of 5–50 s from ambient noise cross-correlation technique. Based on this abundant dataset, we obtained the three-dimensional high resolution Vp and Vs model in the crust and uppermost mantle of southwest (SW) China by adopting the joint body and surface wave travel time tomography method considering the topography effect starting from the first version of community velocity model in SW China (SWChinaCVM-1.0). Compared to SWChinaCVM-1.0, this newly determined velocity model has higher resolution and better data fitness. It is accepted by the China Seismic Experimental Site as the second version of the community velocity model in SW China (SWChinaCVM-2.0). The new model shows strong lateral heterogeneities in the shallow crust. Two disconnected low velocity zones are observed in the middle to lower crust, which is located in the Songpan-Ganzi block and the northern Chuandian block to the west of the Longmenshan-Lijiang-Xiaojinhe fault, and beneath the Xiaojiang fault zone, respectively. The inner zone of the Emeishan large igneous province (ELIP) exhibits a high velocity anomaly, which separates the two aforementioned low velocity anomalies. Low velocity anomaly is also shown beneath the Tengchong volcano. The velocity structures in the vicinity of the 2008 Ms8.0 Wenchuan earthquake, the 2013 Ms7.0 Lushan earthquake and the 2017 Ms7.0 Jiuzhaigou earthquake mainly show high Vp and Vs anomalies and the mainshocks are basically located at the transition zone between the high and low velocity anomalies. Along with the segmentation characteristics of seismic activity, we suggest that areas with significant changes in velocity structures, especially in active fault zones, might have a greater potential to generate moderate to strong earthquakes. [ABSTRACT FROM AUTHOR]

The contemporary carbon balance over the Tibetan Plateau is highly uncertain with a ten-fold difference between various estimates. In a warming world, the potential exists for a large carbon release from its permafrost which could compromise China's 2060 carbon-neutral goal. Here, we used a satellite- and inventory-based approach, ecosystem models, and atmospheric inversions to estimate that the carbon sink was 33.12–37.84 TgC yr−1 during 2000–2015. The carbon sink induced by climate change and increasing CO2 levels largely overcompensated for a livestock grazing-induced carbon source of 0.38 TgC yr−1. By 2060, the carbon sink is projected to increase by 38.3–74.5% under moderate to high emissions scenarios, with the enhanced vegetation carbon uptake outweighing the warming-induced permafrost carbon release. The restoration of degraded grassland could sequestrate an additional 9.06 TgC yr−1, leading to a total carbon sink of 57.78–70.52 TgC yr−1. We conclude that the Tibetan Plateau's ecosystems absorbed two-and-a-half times the amount of its cumulative fossil CO2 emissions during 2000–2015 and that their carbon sinks will almost double in strength in the future, helping to achieve China's pledge to become carbon neutral by 2060. [ABSTRACT FROM AUTHOR]

Asian cultivated rice (Oryza sativa) has two main subspecies, indica (O. sativa sub. indica) and japonica (O. sativa sub. japonica). Japonica rice was domesticated in the middle and lower reaches of the Yangtze River in China, while indica appeared around 4000 a BP in northern south Asia after hybridization between introduced japonica and indigenous proto-indica. When and how indica rice spread into China is still barely understood, although it is cultivated widely in southern China today. Here we report on the earliest, definite indica rice remains in China, including charred seeds, phytoliths, and ancient DNA, from the newly investigated Kongsangqiao site at an elevation of 2676 m above sea level in Tibet, along with a charcoal study that reveals the vegetation and climate during of human occupation. AMS radiocarbon dating of charred indica rice grains suggests the remains are from the 8th century (700s CE). The dominant identified charcoal fragments are Himalayan pine (Pinus wallichiana), from which a rather cold climate is inferred where indica rice could not be grown in situ, suggesting it was likely brought to the site. Both archaeological and literature records thus support that indica rice, fully domesticated in northern south Asia, had spread to the southern margin of the Tibetan Plateau via parts of the ancient Tang-Tubo Road, Tubo-Nepal Road, by at least the 8th century CE. [ABSTRACT FROM AUTHOR]