Research on the Dynamic Change of Regional Stress Fields before the M_S8.0 Wenchuan Earthquake

Using the digital telemetric seismic waveform data of Chengdu and Kunming, this article studies the focal mechanism solutions and the apparent stress values of a large number of small earthquakes, and then analyzes the dynamic variation of regional stress fields and the spatio-temporal distribution of apparent stress values. The annual variation values of the azimuth of average principal stress field before the May 12, 2008 M_S8.0 Wenchuan earthquake in the Sichuan-Yunnan region were 58° from 2003 to 2004, 85° from 2003 to 2005,61° from 2006 to 2007 and 90° from 2006 to April 2008 respectively. In recent years, deflection or disturbances occurred in the azimuth of the average principal stress field in the Sichuan-Yunnan region. Analysis shows that this may be related to the change of stress field states of crustal blocks before and after the December 26, 2004 M_S9.0 Sumatra earthquake and the 2008 M_S8.0 Wenchuan earthquake. The ratio of thrust-type earthquakes in the Sichuan-Qinghai block was on the higher side in the period from 2006 to 2007, and the source faulting type of the regional moderate and small earthquakes had changed before the M_S8.0 Wenchuan earthquake. The change of state of the stress field is consistent with the changes in block displacement fields revealed by GPS data and the crustal shortening velocity vertical to the Longmenshan fault zone. Based on the radiation energy calculated from all bands of the seismic waveform, the value of apparent stress σ_app is obtained. The fluctuation shape of the fitting trend of the apparent stress is related to the intensity of regional seismicity. It reveals that the micro-dynamic fluctuation process of the regional stress value is similar to the azimuth transition of the regional principal compressive stress field, which can be used to probe for pregnant physical processes. Areas with a higher value of apparent stress σ_app are possible areas of potential seismic risk. It can be seen from the spatial distribution of the medium and short-term apparent stress σ_app before the M_S8.0 Wenchuan earthquake, the Longmenshan fault zone is in a low stress distribution area, and the relatively high apparent stress is in the peripheral area. These images may show medium and short-term locking phenomena near the seismogenic tectonics of the M_S8.0 Wenchuan earthquake. For example, changes with time of the focal parameter consistency of the sub-blocks in Sichuan and Yunnan Provinces, continual increase of thrust-type earthquakes in the Sichuan-Qinghai block and the appearance of spatial distribution areas of high apparent σ_app stress. The work on this aspect was continued after the M_S8.0 Wenchuan earthquake, and the results seem to be shown a clearer relationship between these phenomena and future great earthquakes.     

The effects of biodegradation on biomarker maturity indicators in sequentially biodegraded oils from Liaohe Basin,China

By aid of gas chromatogram/mass spectrometry (GC-MS), the distributions and the compositions of biomarkers in a set of sequentially biodegraded oils from Liaohe Basin, China, have been quantitatively analyzed, and it has been found that during the biodegradation process of crude oils, the molecular maturity parameters such as Ts/Tm, homohopane C₃₁ 22S/(22S+22R) and sterane C₂₉ 20S/(20S+20R) ratios will be affected to different extent. The results show that except homohopane C₃₁ 22S/(22S+22R) ratio, Ts/Tm ratio will decrease with increasing biodegradation, but for C₂₉ 20S/(20S+20R) ratio, it will almost remain constant in slightly and moderately biodegraded oils, and then will increase quickly in severely biodegraded oils. The main reason is that there are some differences in the ability of resistant biodegradation for different isomer of biomarkers with different stereo configuration, resulting in the fact that destroying rate by bacteria for those biomarkers with weak ability will be higher than those with strong ability in resistant biodegradation. For example, 18α(H)-22,29,30-trisnorhopanes (Ts) will be destroyed more quickly than 17α(H)-22,29,30-trisnorshopanres (Tm), and 20R isomer is more quickly than 20S isomer for C₂₉ sterane, resulting in the relative ratios changed with increasing biodegradation. Therefore, much more attention should be paid to the biodegradation extent of crude oils and the type of biomarker maturity indicators, when the distributions and the compositions of biomarkers in biodegraded oils are used to determine the maturity of biodegraded oils.     

The effects of biodegradation on the compositions of aromatic hydrocarbons and maturity indicators in biodegraded oils from Liaohe Basin

By the aid of GC-MS technique, a series of sequentially biodegraded oils from Liaohe Basin have been analyzed. The results show that the concentrations and relative compositions of various aromatic compounds in the biodegraded crude oils will change with increasing biodegradation degree. The concentrations of alkyl naphthalenes, alkyl phenanthrenes, alkyl dibenzothiophene are decreased, and the concentration of triaromatic steroids will increase with increasing biodegradation degree in biodegraded oils. Those phenomena indicate that various aromatic compounds are more easily biodegraded by bacteria like other kinds of hydrocarbons such as alkanes, but different series of aromatic compounds have a varied ability to resistant to biodegradation. The ratios of dibenzothiophene to phenenthrene (DBTH/P) and methyl dibenzothiophene to methyl phenanthrene (MDBTH/MP) are related to the features of depositional environment for source rocks such as redox and ancient salinity. However, in biodegraded oils, the two ratios increase quickly with the increase of the biodegradation degree, indicating that they have lost their geochemical significance. In this case, they could not be used to evaluate the features of depositional environment. Methyl phenanthrene index, methyl phenanthrene ratio and methyl dibenzoyhiophene ratio are useful aromatic maturity indicators for the crude oils and the source rocks without vitrinite. But for biodegraded oils, those aromatic maturity indicators will be affected by biodegradation and decrease with the increase of the biodegradation degree. Therefore, those aromatic molecular maturity indicators could not be used for biodegraded oils.     

基于D-InSAR技术的地面沉降监测方法

针对传统地面沉降监测方法的不足,D-InSAR技术因其全天候、空间分辨率高、精度高等优点,在地面沉降监测方面其表现得越来越重要。本文对香港地区的3幅ERS影像进行处理,提取了该地区高精度的三维沉降场,结果表明,该地区最大沉降值为-0.551 6 cm,且沉降趋势较缓慢,分布平均,D-InSAR技术可以有效地提供高精度的地面沉降信息,在地面沉降监测方面具有较高的实用性。     

据地壳速度结构推测1668 年山东郯城8½级大地震震中

分析了1668 年山东郯城8?级大震区附近地壳深部结构特点,以天然地震走时层析成像得到的三维地壳速度结构,主要以中地壳低速层和莫霍面深度为依据,对34°～36°N,118°～119°E区间按经、纬度和斜向扫描,得到相应地壳速度剖面。对比结果,获得与该地震深部结构特点一致的区域,推测震中范围位于34.8°～35.2°N,118.2°～118.7°E,较合理的震中位于35.1°N,118.6°E,震源深度约20km。     

Eigen analysis of tree-ring records: part 2, posing the eigen problem

The technique of expanding meteorological fields on eigenvectors of the field covariation matrix is popular. In this paper, we propose for the first time to use a mathematically similar technique to solve the main problem of dendrochronology: classifying variations in tree-ring records as either age- and microenvironment-dependent or climate-induced. Applying this technique to a sample of very long-lived Qilian junipers (Sabina przewalskii Kom.) from the Dulan region in western China, we demonstrate that the ring-width variations projected on the first eigenvector are age-dependent, but those projected on several of the first subsequent vectors are mainly climate-induced. In particular, the second and third projections capture multi-centennial climatic variations, and the variations projected on the fourth through seventh eigenvectors show periodic variations that are probably induced by the 178-year solar cycle. The projections on the smallest eigenvectors seem to be negligible.     

Climate sensitivity and cloud feedback processes imposed by two different external forcings in an aquaplanet GCM

The sensitivity of climate to an increase in sea surface temperature (SST) and CO₂, as well as cloud feedback processes, is analyzed through a series of aquaplanet experiments listed in the Coupled Model Intercomparison Project. Rainfall is strengthened in a +4K anomaly SST experiment due to the enhanced surface evaporation; while in a quadruple CO₂ experiment, precipitation and total cloud cover are appreciably weakened. In both the +4K and quadruple CO₂ (4xCO₂) experiments, the Hadley cell is impaired, with an increase in moderate subsidence and a decrease in the frequency of strong convective activity. Regarding cloud radiation forcing (CRF), the analysis technique of Bony et al. (Climate Dynamics, 22:71–86, 2004) is used to sort cloud variables by dynamic regimes using the 500-hPa vertical velocity in tropical areas (30°S–30°N). Results show that the tropically averaged CRF change is negative and is dominated mainly by the thermodynamic component. Within convective regimes, the behavior of longwave CRF is different in the +4K and 4xCO₂ experiments, with positive and negative changes, respectively. The globally averaged CRF also reveals a negative change in both aquaplanet and Earthlike experiments, implying that clouds may play a role in decelerating global warming. The calculated climate sensitivity demonstrates that our results are close to those obtained from other models, with 0.384 and 0.584?Km²?W^?1 for aquaplanet and Earthlike experiments, respectively.     

福建热带气旋风雨空间分布特征及风险评估

根据1961—2010年热带气旋资料,按登陆地段或移动路径将登陆影响福建的热带气旋分为11种路径,分析各种路径的致灾因子空间分布特征,结果表明:热带气旋雨灾最严重的区域位于北部和中部沿海,风灾最严重的是南部沿海;从路径来看,降水强度最强是登台入闽北路径,强风区域最大的是直接登陆闽南路径和登台入闽中部路径,风力最强的是登台入闽南路径。采用相关系数客观赋权法建立了致灾因子风险评估模型,分析不同热带气旋路径致灾因子风险等级,登台入闽中和登台入闽北路径风险最大,其次是直接登陆闽南和登陆珠江口及以东路径;高风险区域 (包括次高危险和高危险区) 集中在沿海地区、闽西和闽北的局部。     

Overview of the UAV—Based Eddy Covariance Fluxes Measurements Technique

Airborne Eddy Covariance (EC) method is one of the most effective ways to measure the turbulent fluxes over regional scale directly. The turbulent fluxes from airborne EC method have the same spatial scale with the pixel scale of remote sensing image and the grid scale of land-surface models, which is very important for the simulation of regional or global land-surface fluxes. UAV-based eddy covariance method could achieve the observation of turbulent fluxes in a multi-period and multi-sorties way, and the observation result is reliable and the application is inexpensive. It is an important development direction for airborne flux observation technique. After the introduction of the main technical characteristics of the airborne EC method, this paper reviewed the worldwide progress in UAV-based fluxes measurements system from these aspects of the specifications of the UAVs, the integrated instruments, and the analysis of the application cases. Then, the main sources of uncertainty affecting the UAV-based fluxes measurements were discussed. At last, the shortcomings of the current UAV-based flux observation system were summarized. A brief outlook about UAV-based fluxes measurements technique was also given.