Mercury in sediments of Ulhas estuary

Hg levels in water, suspended particulate matter and sediment of the Ulhas estuary are under considerable environmental stress due to the indiscriminate release of effluents from a variety of industries including chlor-alkali plants. Concentration ranges of dissolved (0.04-0.61 micro gl(-1)) and particulate (1.13-6.43 micro gg(-1)) Hg reveal a definite enhancement of levels in the estuary. The Hg burden in sediment upstream of the weir that limits the tidal influence is low (0.08-0.19 micro gg(-1)) with low C(org) content (1.8-2.9%). The high Hg content of the sediment just below the weir varies seasonally (highest concentration recorded being 38.45 micro gg(-1)) due to incremental accretion of sediment as the fresh water flow over the weir progressively decreases. The 30 km segment of the estuary sustains markedly high levels of Hg in the sediment with an exponential decrease in the seaward direction from the weir. Higher concentrations than the expected background prevail in all the estuarine cores up to the bottom, though the overall concentration decreases from about 20 micro gg(-1) in core 7 (inner estuary) to 1 micro gg(-1) in core 31 (outer estuary). The Hg in sediment is associated with C(org), while its correlation with Al, Fe and Mn is poor. The Hg profiles in cores from the Arabian Sea (stations 34, 35 and 37) have a distinct horizon of enhanced concentration in the 5-60 cm segment. Based on 210Pb dating of core 37, the sediment at the bottom of this core is inferred to have been deposited in the year 1949, roughly two year prior to the establishment of the first chlor-alkali plant and represents the background (0.06-0.10 micro gg(-1)). The Hg profiles in the offshore cores indicate a marked increase in transfer of Hg to sediment subsequent to 1980, with a peak around 1990-1992. Based on the index of geoaccumulation it is considered that the estuarine segment between stations 4 and 23 is extremely polluted, while the sediment from the open coast is moderately polluted in the top 25-30 cm with respect to Hg. The enrichment factor of Hg in the sediment is 350-700 for core 4 and decreases to 0-7 for the open-shore cores.     

耦合应力释放模型的原理及应用

在Vere-Jones提出的应力释放模型的基础上,考虑各部分之间的相互作用,提出耦合应力释放模型,并将该模型应用于华北地区的历史地震目录中．采用AIC判别准则,将该模型所得结果与原有的应力释放模型的结果进行对比,结果表明,耦合应力释放模型优于以前的模型．      

地震预报和地震危险性

回顾就预报地震和地震危险性问题所引出的争论,模型和方法,试图对发生于某一特定时间空间和震级窗内的地震,研究其发生概率定量化的统计方法是本文强调的重点。     

用宽频带区域地震图确定震源参数

近期发展的震源反演方法并没有充分利用区域地震图的宽频带性质,原因是用平行层模型计算的格林函数和真实地壳的复杂传播现象不同。这种反演通常去掉了短周期成分,并且只反演记录中选定的部分。在本文中,我们介绍一种估算震源参数的方法,它可以较好地应用整个宽频带记录,而且只采用目前仅有的不完善的格林函数即可。这个方法通过分别拟合格林函数的各个部分来使得记录图与合成图主要的地壳到达波到时差别不大。确定震源参数的原     

地震活动加速模型及其在中国的应用

运用岩石破裂的亚临界扩展理论,推导出区域地震活动性加速模型的基本公式．我们把中国板内的3个地震块体:华北亚板块、川滇块体和新疆亚板块按地震活动性及构造条件的差异分为7个研究区域,使用Sornette和Sammis的改进公式,分别对每个区域进行地震活动性加速模型分析．对于已经发生过的区域强震,模型能给出与实际强震较接近的震级与发震时间,表明地震活动性加速模型同样能适用于板内的地震活动．文中给出了地震活动加速模型预测的山西地震带、鄂尔多斯地震带、博乐——托克逊地震带和阿因柯——乌恰地震带未来强震可能的发生时间和震级．在同一亚板块内或块体中,各地震带的地震活动期在时间上较为相似．加速模型中参数可以用来表征区域地震活动强度,对于中国大陆,一般为0.4．对于台湾地震带和一些构造活动复杂的地震带,地震活动加速模型目前尚不能预测未来强震的震级和发震时间．      

The concept of "sustainable ecological succession"; and its value in assessing the recovery of sediment seabed biodiversity from environmental impact

The problem of determining whether the biodiversity of an impacted muddy seabed is recovering can be resolved by drawing on a concept termed "sustainable ecological succession". At a site impacted by discharge of mine tailings, a suite of approximately 6 primary opportunist species (mostly polychaete worms) had started to sustain itself within 1-2 years after discharge ceased (1995), within the mix of 100+ other species which were not sustaining themselves. The start of a sustaining ecological succession is easily measurable by repeat surveys, and requires only the services of one taxonomic identifier to demonstrate the consistent presence and numbers of a limited range of species. At the assessed site, by 2000, some secondary opportunist species had entered the succession, and the species richness of the impacted area had come to equal that of the reference areas.