汶川大地震前后GPS观测的精密单历元解得到的震区地壳运动

利用BERNESE软件的单历元观测值双差定位功能,获取了接近2008年5月12日汶川Ms8.0大地震震中5个GPS观测站(PIXI,CHDU,JYAN,NEIJ和LUZH站)震前的短临位移过程及震后短时间的位移.通过拟合和对比分析,讨论了单历元解的精度.计算结果表明,以YANC站为固定站,LUZH站震前5月9日N(南北...     

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Investigation of Coulomb stress changes in south Tibet(central Himalayas) due to the 25th April 2015 M_W 7.8 Nepal earthquake using a Coulomb stress transfer model

After M_W 7.8 Nepal earthquake occurred, the rearrangement of stresses in the crust commonly leads to subsequent damaging earthquakes. We present the calculations of the coseismic stress changes that resulted from the 25 th April event using models of regional faults designed according to south Tibet-Nepal structure, and show that some indicative significant stress increases. We calculate static stress changes caused by the displacement of a fault on which dislocations happen and an earthquake occurs. A M_W 7.3 earthquake broke on 12 May at a distance of * 130 km SEE of the M_W 7.8 earthquake, whose focus roughly located on high Coulomb stress change(CSC) site. Aftershocks(first 15 days after the mainshock)are associated with stress increase zone caused by the main rupture. We set receiver faults with specified strikes, dips,and rakes, on which the stresses imparted by the source fault are resolved. Four group normal faults to the north of the Nepal earthquake seismogenic fault were set as receiver faults and variant results followed. We provide a discussion on Coulomb stress transfer for the seismogenic fault, which is useful to identify potential future rupture zones.     

Multiple processes affecting surface seawater N20 satura- tion anomalies in tropical oceans and Prydz Bay, Antarc- tica

Abstract We analyzed the N20 content of surface seawater sampled from Prydz Bay, Antarctica, on a cruise track between 30°S and 30°N during the twenty-second Chinese National Antarctic Research Expedition during austral summer, 2006. The surface water showed an average pN20 value of 311.9a：7.6 nL.L-1 （14.1：t：0.4 nmol-Ll）, which was slightly undersaturated. The air-sea N2O flux in the region was -0.3±0.8 p.mol.mE,dl; howeveh N20 in the surface water was oversaturated in most stations along the cruise track. Saturation anomalies were greater than 10%, with a maximum of 54.7% being observed at the Eqaator, followed by 31% at 10°N in the Sulu Sea. The air-sea fluxes at these locations were 12.4 and 4 μmol-mLd-1, respectively. Overall, the results indicated that surface water in Prydz Bay was near equilibrium with atmospheric N20, and that ocean waters in lower latitudes acted as a N20 source. Physical processes such as stratification, ice-melt water dilution, and solar radiation dominate the factors leading to N20 saturation of surface water of Prydz Bay, while biological production and upwelling are primarily responsible for the N20 oversaturation of surface water observed in subtropical and tropical regions along the cruise track.     

汶川地震灾区重建若干问题探讨

汶川地震重灾区在四川省涉及51个县(区市),面积约13.28万km2,人口约2 657万.灾区地跨龙门山脉及其东西两侧,西部为青藏高原,东部为成都平原和四川盆地;西部是生物多样性保护中心和长江上游重要生态屏障,但经济发展滞后;而东部是经济较发达地区,人口和经济密度大,城市化和工业化水平较高.灾区重建要立足眼前,着眼长远;用3 a左右时间基本达到灾前水平,再用5～10 a时间将灾区建成工业化、城镇化水平较高、产业结构合理、生态环境优良、人民安居乐业的区域.要坚持以人为本,确保人居环境的安全;要生态优先,突出生态保护的战略地位,规避在生态敏感区建设污染型企业;在成德绵要加快产业集群建设;山区聚落,要变分散为集中,进行空间、产业和组织重构.     

A nearly analytic exponential time difference method for solving 2D seismic wave equations

In this paper, we propose a nearly analytic exponential time difference (NETD) method for solving the 2D acoustic and elastic wave equations. In this method, we use the nearly analytic discrete operator to approximate the high-order spatial differential operators and transform the seismic wave equations into semi-discrete ordinary differential equations (ODEs). Then, the converted ODE system is solved by the exponential time difference (ETD) method. We investigate the properties of NETD in detail, including the stability condition for 1-D and 2-D cases, the theoretical and relative errors, the numerical dispersion relation for the 2-D acoustic case, and the computational efficiency. In order to further validate the method, we apply it to simulating acoustic/elastic wave propagation in multilayer models which have strong contrasts and complex heterogeneous media, e.g., the SEG model and the Marmousi model. From our theoretical analyses and numerical results, the NETD can suppress numerical dispersion effectively by using the displacement and gradient to approximate the high-order spatial derivatives. In addition, because NETD is based on the structure of the Lie group method which preserves the quantitative properties of differential equations, it can achieve more accurate results than the classical methods.     

Fluctuation regimes of soil moisture in ERA-40 re-analysis data

Soil moisture variability is analysed in the re-analysis data ERA-40 of the European Centre for Medium-Range Weather Forecasts (ECMWF) which includes four layers within 189 cm depth. Short-term correlations are characterised by an e-folding time scale assuming an exponential decay, whilst long-term memory is described by power law decays with exponents determined by detrended fluctuation analysis. On a global scale, the short-term variability varies congruently with long-term memory in the surface layer. Key climatic regions (Europe, Amazon and Sahara) reveal that soil moisture time series are non-stationary in arid regions and in deep layers within the time horizon of ERA-40. The physical processes leading to soil moisture variability are linear according to an analysis of volatility (the absolute differences), which is substantiated by surrogate data analysis preserving the long-term memory.     

土壤热导率的研究现状及其进展

土壤热导率是重要的土壤热参数之一, 在下垫面土壤热量的传输中起到重要作用; 同时也是区域气候模式、 陆面过程模式中重要的输入参数, 在预估未来气候变化等方面也具有重要作用. 根据国内外的研究现状, 评述了土壤热导率的影响因素和模拟方案. 其中, 土壤质地、 温度、 含水(冰)量和孔隙度等是影响土壤热导率的主要因素, 特别在研究冻土时需重点分析含冰量的变化. 结合影响因素, 比较分析了典型的国内外计算土壤热导率的模型, 得出这些模型多适用于模拟常温下的热导率, 低温条件如青藏高原冻土区模拟结果并不理想. 因此, 多年冻土区土壤热导率的研究多基于观测资料计算或使用陆面模式中的参数化方案估算, 但因多年冻土内部水热传输过程的复杂性, 青藏高原多年冻土区热导率的模型模拟仍需进一步研究.     

青藏高原近地表土壤不同冻融状态的变化特征及其与气温的关系

近地表层作为陆-气相互作用的重要界面,其土壤的冻融状态可直接或间接的反映陆地表对气候的响应程度。为了探讨青藏高原近地表土壤受气候变化的影响,利用青藏高原87个气象站逐日地表温度资料,结合空间分析技术和数理统计方法,将土壤冻融状态划分为三种状态,即完全冻结状态（CF）、日冻融循环状态（DFT）和完全融化状态（CT）,分析青藏高原1980-2015年近地表不同冻融状态的时空变化及其与气温的关系。研究表明：青藏高原近地表土壤不同冻融状态有明显的时空差异。CF集中在11月-翌年2月,约为2 d;DFT主要出现于10月-翌年4月,每年发生约150 d;CT则主要集中于每年3-10月,出现约217 d。空间分布上,CF主要发生在高原东北部;DFT几乎遍布整个高原,且以冷季出现较多;CT与DFT呈现相反的分布特征。多年冻土区,CF和DFT状态变化较显著;而在非多年冻土区,CT状态变化幅度较大。不同冻融状态与月平均气温（T_mair）也有较好的对应关系：CF主要发生在T_mair<0℃的区间,DFT则发生在T_mair≤17℃区间内,而CT主要出现在T_mair>0℃。