3D P-WAVE VELOCITY STRUCTURE AT THE NORTHEASTERN MARGIN OF ORDOS BLOCK     

HAN Xiao-ming  Liu Fang  ZHANG Fan  CHEN Li-feng  LI Juan  LI Shuan-hu  YANG Hong-ying 《地震地质》2018,40(1):215-231

Using the 7 100 absolute first arrivals of P waves and 91 513 relative P arrival times of 726 events at the northeastern margin of the Ordos block since 2009, the 3D fine structure of P wave velocity within the depth of 15km in the crust was inverted by the double difference seismic tomography method. The results show that there exist obvious high-speed continuous bodies in the northwest of the study area, and their lateral areas increase gradually with depth, while the velocity of east and south is relatively low. The velocity inhomogeneity exists and differs at different depths. The lateral differences of velocity are related to seismicity and faults. The 5~15km depth profile shows that earthquakes tend to occur in the area with relatively high velocity or high speed transition zones, which to some extent reflects the fragility of regional crustal media and the strong differential movement of faults in vertical and horizontal directions where the crust body is easy to absorb and store strain energy and generate major earthquakes. A "Y"-shape low-velocity channel is present in the lower crust around Liangcheng, corresponding to the NW-trending Heilaoyao-Shahukou fault set, which may reveal the migration path of the Late Tertiary-Quaternary basalt eruption. The Helingeer M6.2 earthquake in 1976 was related to the formation of the locking section of the thermal welding in this area. The three-dimensional fine structure of P wave velocity presented in this paper provides intuitive seismological evidence for physical and chemical properties of crustal media and the deep tectonic environment of earthquake preparation.  相似文献   

游客-环境互动视角下旅游者目的地环境恢复性效应     

朱芳  苏勤  陶云  沈惊宏 《热带地理》2020,40(4):636-648

日常生活环境和旅游目的地环境都可以为个体提供恢复的机会，不同环境的属性特征导致不同程度的恢复。为了探究环境类型与恢复性效应之间的关系及停留时间的调节作用，文章采用问卷调查方式，利用配对样本t检验和混合设计方差分析相结合的方法，探讨游客在不同环境中的恢复性效应，并对这一现象提供心理上的解释。结果表明：1）恢复体验的4个维度（放松体验、心理脱离、掌握体验、控制体验）在旅游目的地环境中的得分均高于日常生活环境。2）掌握和控制体验维度在城市旅游目的地中的变化程度高于乡村旅游目的地，两种类型目的地的放松和心理脱离维度差异较小。3）随着在目的地停留时间的延长，乡村旅游目的地放松体验和心理脱离维度变化程度高于城市旅游目的地，两种类型目的地环境恢复性效应会相互靠近。因此，游客的环境恢复性效应不仅受到环境和目的地类型的影响，同时还与游客的适应程度有关，且受到其停留时间的调节作用。  相似文献   

Salinivibrio sp.YH4胞外丝氨酸蛋白酶EYHS耐盐性及生物信息学分析          下载免费PDF全文

武翠玲  宋英达  高慧芳  张廉芸  任晨霞 《盐湖研究》2020,28(1)

摘要：目的 探讨菌株Salinivibrio sp.YH4分泌的丝氨酸蛋白酶EYHS的耐盐性及结构特征。方法 明胶底物酶谱法分析EYHS的耐盐性。应用生物信息学手段对EYHS及6种耐盐的S8家族丝氨酸蛋白酶结构特征进行分析。结果 EYHS在4 mol/L的NaCl溶液中仍具有活性，属于耐盐蛋白酶。EYHS及6种S8家族丝氨酸蛋白酶分子表面的loop区等无规则卷曲所占比例较高，α-螺旋与β-片层则主要位于酶分子内部。EYHS分子表面酸性氨基酸含量较高，且具有弱疏水内核。多序列比对发现蛋白酶的催化三联体两侧存在高度保守的基序和保守的极性氨基酸及芳香族氨基酸，并存在多个保守的Gly与Ala。同源模建和表面电荷分布显示，α螺旋和β片层围成了蛋白酶的催化腔，EYHS活性中心包含由Asp32、His65与Ser215组成的催化三联体，且催化位点区域表面静电势为负。结论 上述结构特征可能有助于耐盐丝氨酸蛋白酶EYHS在高盐环境下维持其稳定性和适度柔性，并有助于其催化功能的发挥，为深入研究耐盐丝氨酸蛋白酶的高盐环境适应性提供了一定的理论依据。  相似文献   

Correspondence between the large volcanic eruptions and ENSO events over AD 1525–2000     

Fang  Xiuqi  Zheng  Xue  Zhang  Xing 《地理学报(英文版)》2020,30(1):103-118

ENSO is an interannual mode which may be affected by external forcing, such as volcanic eruptions. Based on the reconstructed volcanic eruptions chronology and ENSO sequences, both 195 large volcanic eruptions(VEI≥4) and 398 ENSO(El Ni?o and La Ni?a) events were extracted from 1525 to 2000. An analysis of the correspondence between the large volcanic eruptions and ENSO events was performed by matching the large volcanic eruptions with the types and magnitudes of ENSO events present in the 0–2 years after the eruptions. The results show the following:(1) The percentages of ENSO events within the 3 years after the large eruptions had increased to 68.3% from 31.7% compared with those with no-eruptions in the previous 0–2 years. In addition, the ratio of El Ni?o to La Ni?a events turned from 2:3 to 1:1, and more El Ni?o events occurred in the 0 year after eruptions in the low-latitudes of the Northern Hemisphere and in the tropics but more La Ni?a events occurred in the 0 year after in the high-latitudes of the Northern Hemisphere and the Southern Hemisphere.(2) After the eruptions, the weak(W) El Ni?o events had increased by 8 percentage points and the very strong(VS) El Ni?o events had decreased by 10 percentage points; conversely, there was a decrease by 15 percentage points of the weak La Ni?a events and an increase by 11.4 percentage points of the very strong La Ni?a events. Specifically, the percentages of strong La Ni?a events increased to a peak at 1(+1) year after the eruptions.(3) The percentage of eruptions followed by single-year ENSO was the greatest. The percentage of ENSO events that occurred in the consecutive 2 years following an eruption was approximately equal to the percentage of events that occurred consecutively 3 years following an eruption, and both sets of ENSO magnitudes showed a decreasing trend.  相似文献   

城镇化与生态环境耦合的动态模拟——研究进展与展望     

崔学刚  方创琳  刘海猛  刘晓菲  李咏红 《地理学报(英文版)》2020,30(2):333-352

Urbanization and eco-environment coupling is a research hotspot.Dynamic simulation of urbanization and eco-environment coupling needs to be improved because the processes of coupling are complex and statistical methods are limited.Systems science and cross-scale coupling allow us to define the coupled urbanization and eco-environment system as an open complex giant system with multiple feedback loops.We review the current state of dynamic simulation of urbanization and eco-environment coupling and find that:(1)The use of dynamic simulation is an increasing trend,the relevant theory is being developed,and modeling processes are being improved;(2)Dynamic simulation technology has become diversified,refined,intelligent and integrated;(3)Simulation is mainly performed for three aspects of the coupling,multiple regions and multiple elements,local coupling and telecoupling,and regional synergy.However,we also found some shortcomings:(1)Basic theories are inadequately developed and insufficiently integrated;(2)The methods of unifying systems and sharing data are behind the times;(3)Coupling relations and the dynamic characteristics of the main driving elements are not fully understood or completely identified.Additionally,simulation of telecoupling does not quantify parameters and is not systemically unified,and therefore cannot be used to represent spatial synergy.In the future,we must promote communication between research networks,technology integration and data sharing to identify the processes governing change in coupled relations and in the main driving elements in urban agglomerations.Finally,we must build decision support systems to plan and ensure regional sustainable urbanization.  相似文献   

青藏铁路沿线不同类型挡沙墙阻沙率     

杨印海  薛春晓  石龙  李凯崇  孔令伟  张芳 《中国沙漠》2020,40(1):173-178

基于风洞试验对青藏铁路沿线不同类型防沙措施防沙效果进行模拟研究，探讨了不同类型挡沙墙的防沙效果。结果表明：挂板式、轨枕式和箱式挡沙墙输沙率随高度基本呈递增缓变型趋势，最大输沙率低于20%；铃铛式和高立式聚乙烯（PE）网挡沙墙随高度呈递减陡降型趋势，距地表6~8 cm处为转折点，转折点以上输沙率随高度增大急剧减小，转折点以下输沙率随高度变化较为平缓，最大输沙率低于50%。随着风速的增大，各挡沙墙的阻沙率呈递减趋势：挂板式和轨枕式挡沙墙对风速的敏感性最弱，整体阻沙效果较优，可大范围推广；箱式挡沙墙对风速的敏感性较弱，建议在风速18 m·s^-1以下的地区使用；PE网挡沙墙防沙效果对风速的敏感性最强，建议在风速10 m·s^-1以下的地区使用。  相似文献   

Spatial Variations of b-Values in the Coastal Area of Guangdong     

ZHOU Pengxiang  XIA Shaohong  SUN Jinlong  CAO Jinghe  XU Huilong  ZHAO Fang  CHEN Chuanxu 《中国海洋大学学报(英文版)》2018,(1)

We used earthquake catalogs recorded by Guangdong Seismological Network from 2008 to 2014 to resolve the spatial variations of b-values in the coastal area of Guangdong, particularly in three key research areas(Yangjiang, Heyuan, and offshore Nanao Island) with strong seismicity. Our results revealed that b-values exhibited significant spatial variations, and zones with low b-values could indicate the most likely seismogenic area of large earthquakes. We observed three clear low b-value patches in the offshore Nanao Island. We found a distinct high b-value peak at the depth of 11 km and two minimum peaks at about 14 and 7–8 km in the Yangjiang area. The overall b-values generally decrease with depth in the Heyuan area. The spatial variations of b-values reflect tectonic anomalies; that is, the ‘low-high-low' distribution of b-values in the offshore Nanao Island and the Yangjiang area may indicate the anomaly of the crustal structure with a weak layer. The b-values of reservoir-induced seismicity are obviously lower than that induced by tectonism. This finding indicates that the reservoir area is generally at high stress state under the condition of high pore pressure. We inferred that large earthquakes might be prone to occur at 10–12 km depth in the offshore Nanao Island, at 12–15 km depth in the Yangjiang area, and at the lower part of the seismic activity zone in the Heyuan area. Moreover, the upstream area of the Xinfengjiang reservoir is the most likely area of future large earthquakes in the Heyuan area.  相似文献   

Rising grain prices in response to phased climatic change during 1736–1850 in the North China Plain     

Wen  Yanjun  Fang  Xiuqi  Liu  Yang  Li  Yikai 《中国科学:地球科学(英文版)》2019,62(11):1832-1844

Grain price volatility during historical periods is regarded as an important indicator of the impact of climate change on economic system, as well as a key link to adjust food security and social stability. The present study used the wheat prices in Baoding Prefecture, China, during 1736–1850 to explore connections between climatic transition and grain price anomalies in the North China Plain. The main findings were as follows:(1) The grain price change showed an apparent correspondence with climatic transition. The period 1781–1820 was a transition phase, with more extremes and decreased precipitations when the climate shifted from a warm phase to a cold one. Corresponding with the climatic transition, the grain price during 1781–1820 was characterized by that the mean of the original grain price series was significantly higher(lower) than the previous(later)phase, and the variance and anomaly amplitude of the detrended grain price series was the highest during 1736–1850.(2) The correspondence between grain price extremes and drought events occurred in phases. Five grain price extremes occurred following drought events during 1781–1810, while extreme droughts were the direct cause of the grain price spike during 1811–1820.(3) Social stability affected by climate change also played an important role in the grain price spike between 1811 and 1820. Paralleling the pathway of "precipitation-grain production-grain price", climate change could have an impact on grain price via the pathway of "precipitation-grain production-grain price-famine-uprising-grain price", as shown during the Tianli Uprising in 1813. These findings could contribute to an improved understanding of the interaction between climate change and human society during the historical period.  相似文献   

Loading protocols for experimental seismic qualification of members in conventional and emerging steel frames     

Cheng Fang  Yiwei Ping  Yiyi Chen 《地震工程与结构动力学》2020,49(2):155-174

Quasi-static testing is one of the most commonly used experimental methods for examining the seismic performance of structural members. However, consistent loading protocols for experimental seismic qualification of members in emerging steel frames such as self-centering braced frames (SCBFs) as well as in some conventional ones including buckling-restrained braced frames (BRBFs) are still lacking. This paper aims to propose standardized loading protocols based on time-history dynamic analysis on a series of prototype building frames, including steel SCBFs, BRBFs, and moment-resisting frames (MRFs), where both far-field and near-fault earthquakes are considered. The methodology for the development of the loading protocols involves ground motion selection and scaling, design and analysis of prototype buildings, analysis results processing, and rainflow cycle counting, together with extra justification steps. The proposed loading protocols are consistently derived based on the MCE-level seismic hazard and 84^th percentile values of key seismic demand parameters. These parameters are number of damaging cycles N_t, maximum inter-story drift θ_max, inter-story drift range Δθ_i, sum of inter-story drift range ΣΔθ_i, and residual inter-story drift θ_r. The analysis confirms the variations in these seismic demands imposed on the different structural systems under different types of ground motions, highlighting the necessity of developing separate loading protocols for the different cases. The assumptions, decisions, and judgments made during the development of the loading protocols are elaborated, and the conditions and restrictions are outlined. The rationality of the proposed loading protocols is further justified through demonstrating the cumulative distribution function and energy dissipation demand of the systems.  相似文献   

基于Sentinel-2的潮间红树林提取方法   总被引：1，自引：0，他引：1  

徐芳  张英  翟亮  刘佳  谷祥辉 《测绘通报》2020,(2):49-54

位于潮间带的红树林可能在高潮时被海水淹没的特点，使得传统的植被提取方法在红树林信息提取方面存在局限性。本文在对比分析了出露的红树林、高潮水位淹没的红树林、海水水体的光谱特征后，提出了一种利用归一化潮间红树林指数（NIMI）提取潮间带红树林的方法。该指数是由植被强吸收的红波段，强反射的两个红边波段和近红外波段组成的归一化表达式。利用该指数对福建省龙海九龙江口湿地的红树林进行了分类提取，提取结果与高分二号影像目视验证和现场调查结果进行了对照。结果显示，该方法提取红树林的用户精度达到93.98%，并显著优于利用归一化水体指数（NDWI）、归一化植被指数（NDVI）及随机森林的结果。  相似文献