Internal structure of Longmenshan fault zone at Hongkou outcrop,Sichuan,China,that caused the 2008 Wenchuan earthquake

This paper reports the internal structures of the Beichuan fault zone of Longmenshan fault system that caused the 2008 Wenchuan earthquake, at an outcrop in Hongkou, Sichuan province, China. Present work is a part of comprehensive project of Institute of Geology, China Earthquake Administration, trying to understand deformation processes in Longmenshan fault zones and eventually to reproduce Wenchuan earthquake by modeling based on measured mechanical and transport properties. Outcrop studies could be integrated with those performed on samples recovered from fault zone drilling, during the Wenchuan Earthquake Fault Scientific Drilling （WFSD） Project, to understand along-fault and depth variation of fault zone properties. The hanging wall side of the fault zone consists of weakly-foliated, clayey fault gouge of about 1 m in width and of several fault breccia zones of 30-40 m in total width. We could not find any pseudotachylite at this outcrop. Displacement during the Wenchuan earthquake is highly localized within the fault gouge layer along narrower slipping-zones of about 10 to 20 mm in width. This is an important constraint for analyzing thermal pressurization, an important dynamic weakening mechanism of faults. Overlapping patterns of striations on slickenside surface suggest that seismic slip at a given time occurred in even narrower zone of a few to several millimeters, so that localization of deformation must have occurred within a slipping zone during coseismic fault motion. Fault breccia zones are bounded by thin black gouge layers containing amorphous carbon. Fault gouge contains illite and chlorite minerals, but not smectite. Clayey fault gouge next to coseismic slipping zone also contains amorphous carbon and small amounts of graphite. The structural observations and mineralogical data obtained from outcrop exposures of the fault zone of the Wenchuan earthquake can be compared with those obtained from the WFSD-1 and WFSD-2 boreholes, which have been drilled very close to the Hongkou outcrop. The presence of carbon and graphite, observed next to the slipping-zone, may affect the mechanical properties of the fault and also provide useful information about coseismic chemical changes.

Internal structures and high-velocity frictional properties of Longmenshan fault zone at Shenxigou activated during the 2008 Wenchuan earthquake

This paper reports internal structures of a wide fault zone at Shenxigou,Dujiangyan,Sichuan province,China,and high-velocity frictional properties of the fault gouge collected near the coseismic slip zone during the 2008 Wenchuan earthquake.Vertical offset and horizontal displacement at the trench site were 2.8 m（NW side up）and 4.8 m（right-lateral）,respectively.The fault zone formed in Triassic sandstone,siltstone,and shale about 500 m away from the Yingxiu-Beichuan fault,a major fault in the Longmenshan fault system.A trench survey across the coseismic fault,and observations of outcrops and drill cores down to a depth of 57 m revealed that the fault zone consists of fault gouge and fault breccia of about0.5 and 250-300 m in widths,respectively,and that the fault strikes N62°E and dips 68° to NW.Quaternary conglomerates were recovered beneath the fault in the drilling,so that the fault moved at least 55 m along the coseismic slip zone,experiencing about 18 events of similar sizes.The fault core is composed of grayish gouge（GG） and blackish gouge（BG） with very complex slip-zone structures.BG contains low-crystalline graphite of about 30 %.High-velocity friction experiments were conducted at normal stresses of 0.6-2.1 MPa and slip rates of 0.1-2.1 m/s.Both GG and BG exhibit dramatic slip weakening at constant high slip rates that can be described as an exponential decay from peak friction coefficient lpto steadystate friction coefficient lssover a slip-weakening distance Dc.Deformation of GG and BG is characterized by overlapped slip-zone structures and development of sharp slickenside surfaces,respectively.Comparison of our data with those reported for other outcrops indicates that the high-velocity frictional properties of the Longmenshan fault zones are quite uniform and the high-velocity weakening must have promoted dynamic rupture propagation during the Wenchuan earthquake.

Spatial variations and mechanisms for the stability of terrestrial carbon sink in China

Understanding the stability of terrestrial carbon sinks(S-TCS)contributes to more accurate prediction of the terrestrial carbon sink(TCS)in the context of future global change and helps inform climate change mitigation policies.Here,focusing on China,we analyzed the spatial distribution and driving mechanisms for the S-TCS,quantified by the interannual variability of the TCS,using three independent approaches(atmospheric inversions,ecosystem carbon cycle models,and machine learning models based on flux tower observations).We found that the interannual variability of the TCS in China is relatively small compared with the conterminous United States and geographic Europe,indicating a generally stable TCS in China.Spatially,the S-TCS is lower in the North China Plain,Northeast China Plain,and western Yunnan-Guizhou Plateau than in other regions,with varying underlying mechanisms.Large interannual variations in precipitation and high TCS sensitivities to precipitation fluctuations explain the low S-TCS in the North China Plain and Northeast China Plain,while high TCS sensitivities to temperature variations drive the low S-TCS in the western Yunnan-Guizhou Plateau.Our findings highlight the importance of considering local contexts for stabilizing and enhancing China’s TCS in a changing environment.

中国碳收支:1980~2021年

As one of the world's largest emitters of greenhouse gases,China has set itself the ambitious goal of achieving carbon peaking and carbon neutrality.Therefore,it is crucial to quantify the magnitude and trend of sources and sinks of atmospheric carbon dioxide(CO_(2)),and to monitor China's progress toward these goals.Using state-of-the-art datasets and models,this study comprehensively estimated the anthropogenic CO_(2)emissions from energy,industrial processes and product use,and waste along with natural sources and sinks of CO_(2)for all of China during 1980-2021.To recognize the differences among various methods of estimating greenhouse emissions,the estimates are compared with China's National Greenhouse Gas Inventories(NGHGIs)for 1994,2005,2010,2012,and 2014.Anthropogenic CO_(2)emissions in China have increased by 7.39 times from 1980 to 12.77 Gt CO_(2)a^(-1)in 2021.While benefiting from ecological projects(e.g.,Three Norths Shelter Forest System Project),the land carbon sink in China has reached 1.65 Gt CO_(2)a^(-1)averaged through 2010-2021,which is almost 15.81 times that of the carbon sink in the 1980s.On average,China's terrestrial ecosystems offset 14.69%±2.49%of anthropogenic CO_(2)emissions through 2010-2021.Two provincial-level administrative regions of China,Xizang and Qinghai,have achieved carbon neutrality according to our estimates,but nearly half of the administrative regions of China have terrestrial carbon sink offsets of less than 10%of anthropogenic CO_(2)emissions.This study indicated a high level of consistency between NGHGIs and various datasets used for estimating fossil CO_(2)emissions,but found notable differences for land carbon sinks.Future estimates of the terrestrial carbon sinks of NGHGIs urgently need to be verified with process-based models which integrate the comprehensive carbon cycle processes.

Changes of net primary productivity in China during recent 11 years detected using an ecological model driven by MODIS data

Net primary productivity （NPP） is an important component of the terrestrial carbon cycle. Accurately mapping the spatial-temporal variations of NPP in China is crucial for global carbon cycling study. In this study the process-based Boreal Ecosystem Productivity Simulator （BEPS） was employed to study the changes of NPP in China＇s ecosystems for the period from 2000 to 2010. The BEPS model was first validated using gross primary productivity （GPP） measured at typical flux sites and forest NPP measured at different regions. Then it was driven with leaf area index （LAI） inversed from the Moderate Resolution Imaging Spectroradiometer （MODIS） reflec- tance and land cover products and meteorological data interpolated from observations at753 national basic meteorological stations to simulate NPP at daily time steps and a spatial resolution of 500m from January 1, 2000 to December 31, 2010. Validations show that BEPS is able to capture the seasonal variations of tower-based GPP and the spatial variability of forest NPP in different regions of China. Estimated national total of annual NPP varied from 2.63 to 2.84Pg C.yr-1, averaging 2.74Pg C.yr-1 during the study period. Simulated terrestrial NPP shows spatial patterns decreasing from the east to the west and from the south to the north, in association with land cover types and climate. South-west China makes the largest contribution to the national total of NPP while NPP in the North-west account for only 3.97% of the national total. During the recent 11 years, the temporal changes of NPP were heterogamous. NPP increased in 63.8% of China＇s landmass, mainly in areas north of the Yangtze River and decreased in most areas of southern China, owing to the low temperature freezing in early 2008 and the severe drought in late 2009.

Climate warming increases biodiversity of small rodents by favoring rare or less abundant species in a grassland ecosystem

Our Earth is facing the challenge of accelerating climate change,which imposes a great threat to biodiversity.Many published studies suggest that climate warming may cause a dramatic decline in biodiversity,especially in colder and drier regions.In this study,we investigated the effects of temperature,precipitation and a normalized difference vegetation index on biodiversity indices of rodent communities in the current or previous year for both detrended and nondetrended data in semi-arid grassland of Inner Mongolia during 1982-2006.Our results demonstrate that temperature showed predominantly positive effects on the biodiversity of small rodents;precipitation showed both positive and negative effects;a normalized difference vegetation index showed positive effects;and cross-correlation function values between rodent abundance and temperature were negatively correlated with rodent abundance.Our results suggest that recent climate warming increased the biodiversity of small rodents by providing more benefits to population growth of rare or less abundant species than that of more abundant species in Inner Mongolia grassland,which does not support the popular view that global warming would decrease biodiversity in colder and drier regions.We hypothesized that higher temperatures might benefit rare or less abundant species(with smaller populations and more folivorous diets)by reducing the probability of local extinction and/or by increasing herbaceous food resources.

Terrestrial carbon cycle model-data fusion:Progress and challenges

The terrestrial carbon cycle is an important component of global biogeochemical cycling and is closely related to human well-being and sustainable development.However,large uncertainties exist in carbon cycle simulations and observations.Model-data fusion is a powerful technique that combines models and observational data to minimize the uncertainties in terrestrial carbon cycle estimation.In this paper,we comprehensively overview the sources and characteristics of the uncertainties in terrestrial carbon cycle models and observations.We present the mathematical principles of two model-data fusion methods,i.e.,data assimilation and parameter estimation,both of which essentially achieve the optimal fusion of a model with observational data while considering the respective errors in the model and in the observations.Based upon reviewing the progress in carbon cycle models and observation techniques in recent years,we have highlighted the major challenges in terrestrial carbon cycle model-data fusion research,such as the“equifinality”of models,the identifiability of model parameters,the estimation of representativeness errors in surface fluxes and remote sensing observations,the potential role of the posterior probability distribution of parameters obtained from sensitivity analysis in determining the error covariance matrixes of the models,and opportunities that emerge by assimilating new remote sensing observations,such as solar-induced chlorophyll fluorescence.It is also noted that the synthesis of multisource observations into a coherent carbon data assimilation system is by no means an easy task,yet a breakthrough in this bottleneck is a prerequisite for the development of a new generation of global carbon data assimilation systems.This article also highlights the importance of carbon cycle data assimilation systems to generate reliable and physically consistent terrestrial carbon cycle reanalysis data products with high spatial resolution and longterm time series.These products are critical to the accurate estimation of carbon cycles at the global and regional scales and will help future carbon management strategies meet the goals of carbon neutrality.