CHARACTERISTICS OF TECTONIC MIXTITE ZONE IN THE LANCANG RIVER,WESTERN YUNNAN

CHARACTERISTICS OF TECTONIC MIXTITE ZONE IN THE LANCANG RIVER,WESTERN YUNNAN     

中国大陆古地震研究的关键技术与案例解析(1)——走滑活动断裂的探槽地点、布设与事件识别标志

古地震研究的主要目标是识别或揭露地质地貌记录的大地震变形遗迹,确定大地震发生的时间、复发特征、同震位移量等参数。要实现这样的目标,探槽开挖地点能否完整记录晚第四纪发生的古地震事件、能否获取大量的测年样品以控制事件发生的年代、能否正确地识别这些事件等是关键,并直接关系到未来大地震危险性评价的可靠性。由于走滑断裂位移发生的特殊性,好的探槽研究地点并不普遍。文中在综合分析走滑断裂同震地表变形特征、影响因素的基础上,通过案例分析,总结出可能成为走滑断裂古地震研究和探槽开挖的候选地点,如洼地、盆地、槽谷、断塞塘、被同步位移连续错开的冲沟床、连续的坎前堆积地层和多级地貌面连续变形等。组合探槽或三维探槽应该是走滑断裂探槽布设的首选。跨断层微地貌位错、断错地层以及上覆更新地层、局部坎前堆积和裂缝充填堆积、不同地层单元沿断层面位移量的突然增加或降低、不同程度的弯曲变形、不同期次的古断塞塘(坑)堆积等,可以作为重要的事件识别依据。要降低古地震识别的不确定性,需要理顺研究程序,明确技术方案,逐一精心实施。认识和结论的得出需要反复推敲,并广泛讨论,同时需要注意细节以及各种信息的相互补充和印证。     

Implications of Arctic industrial growth and strategies to mitigate future vessel and fishing gear impacts on bowhead whales

The objective of this paper was to investigate and illustrate how insights gained from experience managing human activities in order to protect North Atlantic right whales (Eubalaena glacialis) along the heavily industrialized east coast of North America might be applied in the Arctic, where bowhead whales (Balaena mysticetus) face some of the same risks as right whales. The reduced extent and thickness of sea ice and the resultant longer open-water season have major, complex implications for the Arctic marine ecosystem. Increased maritime ship traffic and commercial fishing in the Arctic are bound to affect bowheads and Native (indigenous) hunting communities who depend on whales for subsistence and cultural identity. Bowheads and right whales were greatly depleted by commercial whaling in the 19th and early 20th centuries. While the Western Arctic bowhead population has been recovering steadily in recent decades, North Atlantic right whales remain highly endangered because of persistent lethal and sublethal vessel strikes and frequent entanglement in commercial fishing gear. Entanglement can be transitory or persistent, with debilitation lasting for months before the animal finally succumbs. Vessel strike and fishing gear trauma has been documented in bowheads, but at a much lower rate than in right whales. Initiatives intended to mitigate the impacts of ship traffic on North Atlantic right whales have included speed limits and routing changes. Those meant to reduce the incidence and severity of entanglements include the modification of gear design and gear deployment practices. Management measures need to be considered in advance in the Arctic in order to minimize the risks to bowhead whales as shipping and industrial fishing expand in the Arctic with ice retreat.     

The Schumann resonance: A tool for exploring the atmospheric environment and the subsurface of the planets and their satellites

The propagation of extremely low frequency (ELF) electromagnetic waves and resonance phenomena in the Earth atmosphere has been extensively studied, in relation with ionospheric dynamics, and thunderstorm and lightning activities. A similar investigation can be performed for any other planet and satellite environment, provided this body is wrapped into an ionosphere. There are, however, important differences between Earth and other bodies, regarding the surface conductivity, the atmospheric electron density, the ionospheric cavity geometry, and the sources of electromagnetic energy. In a first approximation, the size of the cavity defines the range of the resonance frequency; the electron density profile, up to the upper atmospheric boundary, controls the wave attenuation; the nature of the electromagnetic sources influences the field distribution in the cavity; and the body surface conductivity, which gives the reflection and transmission coefficients, indicates to what extent the subsurface can be explored. The knowledge of the frequencies and attenuation rates of the principal eigenmodes provides unique information about the electric properties of the cavity. Instruments capable of monitoring the electromagnetic environment in the ELF range are, therefore, valuable payload elements on balloons, descent probes and landers. We develop models for selected inner planets, gaseous giants and their satellites, and review the propagation process of ELF electromagnetic waves in their atmospheric cavities, with a particular emphasis on the application of the Schumann resonance observation to subsurface studies. The instrumentation suitable for monitoring the electromagnetic environment in geophysical cavities is briefly addressed.     

Evidence of electrical activity on Titan drawn from the Schumann resonances sent by Huygens probe

A procedure is shown for extracting weak resonances from the responses of electromagnetic systems excited by electric discharges. The procedure, based on analysis of the late-time system response, is first checked using an analytical function and later with the data for the electric field generated by the computational simulation of Titan's atmosphere using the Transmission Line Matrix (TLM) method. Finally, the low frequency spectrum of the natural electric field in Titan's atmosphere sent by the mutual impedance sensor (MIP) included in the Huygens probe is analyzed employing this technique. The MIP sensor was initially designed to measure the horizontal component of the electric field during a quiet descent. Fortunately, the swinging that occurred during the descent allowed the MIP to measure the radial component of the electric field mixed with the horizontal one. Application of the late-time analysis technique shown in this paper confirms the signature of lightning reported by preliminary data observations, bringing out the expected eigenfrequencies of the Titan-ionosphere electromagnetic cavity, known as Schumann resonances. These resonances are the resonant frequencies of the lower TM^r (transverse magnetic to r) modes, which are quasi-transverse electromagnetic modes because they present vertical or radial components of the electric field two orders of magnitude higher than the associated horizontal, azimuthal and zenithal, components. The sequence of Schumann resonances is unique for each celestial body with an ionosphere, since these resonances are fully determined by the dimensions of the planet or satellite and the corresponding atmospheric conductivity profile. Detecting these frequencies in an atmosphere is clear proof of electrical activity, since it implies the existence of an electromagnetic-energy source, which is essential to create and maintain them.     

卫星观测到的我国闪电活动的时空分布特征

利用卫星上携带的闪电探测仪所获取的8年闪电资料,对我国闪电活动的空间分布、季节变化和日变化等特征进行了分析。结果表明：按照闪电活动的频繁程度在空间上可以将我国大致分为与太平洋海岸平行的4条闪电活动带：即近海区域、中部区域、西部区域和西部边境区域。其中,东南近海区域是我国闪电活动最频繁的地区,并向西北地区逐渐减弱,而西部地区则是我国闪电活动最弱的地区。我国的闪电活动呈现出明显的季节变化和日变化,平均而言,闪电活动主要集中在夏季(约占全年总闪电活动的68％),并以8月份最为活跃,春季次之(约占全年总闪电活动的24％),然后是秋季,冬季最弱,并在11月份出现闪电活动的最小值。在各个季节,随着纬度的减小闪电活动呈现出明显增大的趋势。闪电活动的日变化表明,我国的闪电活动绝大多数发生在午后至傍晚时分,这也与对流活动相对应,而少数地区发生在夜间。     

闪电产生氮氧化物(LNOx)全球特征计算

利用(美国)国家航空和宇宙航行局(NASA)通过卫星上的光学瞬态探测器(OTD)观测到的闪电资料,从计算闪电能量入手,对闪电产生氮氧化物量(NOx)的时空分布进行了计算分析。结果表明,全球LNOx大部分集中在南北半球低纬地区,约占65％,南北基本对称,但中高纬地区南北不对称,北半球产N量远大于南半球,呈现很大的不对称性。全球有6大雷暴群,其中非洲中南部的雷暴群产N量比例最大,占全球总量的近四分之一;其次是北美和南美。中国LNOx量较大的区域主要集中在长江以南的地区,年平均LNOx量占全球的7．8％,青藏高原占中国地区的9．1％～12．2％,5年平均为10．2％。全球各季节的平均产N量分别为42．5kt(春)、67kt(夏)、51．4kt(秋)、37．4kt(冬),全年全球平均闪电产N量估计为200kt。     

国内外洞穴旅游安全研究综述

安全是洞穴旅游的生命线,是洞穴旅游活动正常开展的前提和保障。利用CNKI、维普数据、Springer Link、Elsevier SDOL、EBSCO、SAGE JOURNALS、Wiley等中外文数据库并结合纸质文献,共获得与洞穴旅游安全相关的文献79篇。通过文献梳理发现:洞穴旅游安全是一个研究时间短暂的新兴学术领域,至今仅有25年的研究历史;研究成果较为分散,主题不突出,现有研究成果多属于洞穴或洞穴旅游研究中的“捎带”成果,至今尚无以洞穴旅游安全为主题的独立研究成果;现有研究成果主要涉及洞穴旅游安全的表现、影响因素以及对策等领域,研究内容限于浅表层次;研究尺度以微观为主。洞穴旅游安全作为洞穴旅游的新分支,是一个新的研究领域,在未来应综合运用洞穴学、安全学、旅游学等的相关理论与方法,从确保洞穴旅游环境、旅游者、旅游从业者等安全的角度出发,扩展洞穴旅游安全研究的内容;近期可着重对其理论架构、安全认知、安全风险评估以及安全救援体系等展开研究。      

卫星观测到的青藏高原雷电活动特征

利用TRMM卫星上携带的闪电探测系统获取的闪电定位资料首次对青藏高原上的闪电活动进行了研究。研究发现,青藏高原上的闪电活动呈现出大陆性气候特征,但是受其特殊地形的热力和动力特征所调制,高于93％的闪电活动发生于5—9月之间,并在夏季出现单一闪电活动峰值。随着地表加热和湿度的增加,闪电活动在5月份开始明显增加。较高的闪电密度发生在高原的中部,揭示了闪电活动与地形特征的相关性。63％的闪电活动发生于14：00—18：00(地方时,下同)之间,而只有＜3％的闪电发生于00：00—l0：00之间。闪电光辐射能的时平均值也呈现出明显的日变化,随着太阳的升起,闪电光辐射能在08：00开始增加,并在l0：00达到稳定的极大值,直到02：00开始明显减小。闪电的光辐射能在高原北部呈现最大值,高原西部呈现最小值。青藏高原上的闪电放电强度比其它地区弱得多,其差别归因于高原上较低的对流不稳定能量。     

雷暴过程中闪电产生NOx的地面观测研究

利用NOx分析仪和大气平均电场仪在青海省大通县对雷暴天气过程中自然闪电产生的NOx进行了地面观测。分析结果表明:在晴天稳定大气条件下,全天NOx的平均体积混合比相对比较平稳,观测值虽然比理想中的干净背景大气条件下的地面值要大一些,但比污染大气中的值小许多;在雷暴天气中,闪电次数与NOx的平均体积混合比峰值个数相同,且峰值由闪电产生。闪电产生的NOx的平均体积混合比峰值在出现时间上比闪电有一定的滞后。雷暴过程中各次闪电产生NOx的传输时间序列变化,可用二次多项式进行拟合,且相关系数较高,传输时间和传输距离之间不存在严格的线性关系。高、低能量闪电的能量域值为12～13×106J,高、低能量的闪电是间隔发生的,且随着时间的推移间隔增大。