Geochemical characteristics of soil gas in the Yanhuai basin,northern China

The geochemical backgrounds and origins of soil gases in the Yanhuai basin are discussed based on the regional seismogeological data and concentrations of Rn,Hg,CO2,H2,He and CH4 in soil gas measured at 422 investigating sites in field during September to October 2007.The geochemical background values of Rn,Hg,CO2,H2,He and CH4 are(8105.8±5937.4) Bq/m3,(9.7±5.8) ng/m3,(395.9±35.3)×10-6,(4.0±2.3)×10-6,(15.9±10.4)×10-6 and(12.7±8.1)×10-6,respectively.The geochemical backgrounds of the soil gases are higher in...     

汶川8.0级地震前紫坪铺水库小震活动及震源参数研究

利用区域和水库地震台网记录的数字地震波资料,研究了汶川8.0级地震前的2000年1月1日～2008年5月11日紫坪铺水库区的地震活动及震源参数.结果表明:汶川8.0级地震前该区域小震活动持续,地震活动水平为M_L2～3,自2005年9月紫坪铺水库蓄水以来,特别是2008年2月地震活动明显增加,但从长期的序列来看,地震活动频次和强度仍在区域地震活动的正常起伏范围.汶川8.0级地震发生前近3个月内,中小地震的视应力差值△σ_(app)普遍大于0,计算得到的视应力总大于其拟合值.汶川8.0级地震震中位于低应力区,而相对较高的视应力差值分布在震中以东地区,局部出现视应力增加的现象.     

邵武-河源断裂带中段重磁、垂直形变场特征及其与地震的关系

综合利用流动重磁和流动跨断层短水准复测资料, 分析了邵武-河源断裂带中段重磁场和地壳形变场的时空强变化特征.结果表明:地磁场的变化与监测区的地震活动有较好的对应关系,在震源区附近会出现重力场变化的异常梯度带;断裂两盘垂直形变受区域断裂控制,其差异性变化有指示局部地区孕震活动的作用.     

兰州兴隆山北缘断裂新活动特征的初步研究

兴隆山北缘断裂是兰州盆地南侧边界断裂,也是兰州地区最重要的活动断裂之一,全长约54 km,呈东段NW走向西段近EW走向的弧形断裂.在加里东和燕山运动期,兰州地区在近NE-SW向主压应力下,断裂主要表现为由南西向北东的逆冲活动性质.新生代以来(喜马拉雅运动期),主压应力方向改变为NNE-SSW方向,断裂活动性质也随之发生改变,东段新活动表现为逆左旋运动,西段表现为正左旋运动.断裂的最新活动时代应为晚更新世早～中期,可能与兰州黄河Ⅲ级阶地的形成年代相对应.     

首都圈地区现今地壳垂直形变特征

利用首都圈地区1998、2001、2005、2007年151期精密水准复测资料,分析该区近十年来地壳垂直形变状态与动态特征。结果表明,形变场以继承性运动为主,即山区上升、盆地及平原下降。值得注意的是首都圈西部地区等值线分布密集有序,有些象限图形特征,东西升,南北降,其最大差值为10mm／a,可能预示该区应力场处于逐步积累及有所加强的势态,虽然异常形变数值及所涉面积均较小,但仍需跟踪关注。     

2007年6月3日云南宁洱6.4级地震异常特征分析

通过对2007年6月3日滇西南宁洱6.4级地震前地震活动和前兆异常跟踪,震前对该地震作了短期预测.宁洱6.4级地震前,云南和滇西南地区的6级、5.8级以上地震出现了长时间的平静,显示了能量的积累过程;中期阶段4.5～5.0级地震在震中区周围形成了地震密集区,中、短期阶段滇西南地区MS≥3地震活动显著增强并形成空区,空区长轴250 km,计算震级为6.37,这与实际发生地震震级完全一致.滇西南地区的前兆异常显示,距离震源区近的以趋势异常为主,外围异常以突变为主.     

赤峰--辽蒙交界地区地震活动性及平均波速比分析

分析了赤峰地区地质构造特征、地球动力学环境、历史中强地震活动,表明该区域具备发生中强地震的构造条件;2008年以来的地震活动表明,辽蒙交界地区存在发生5级以上中强震的危险性,该地区的波速比震前异常能够为该地区的地震中期预测提供一定的判定依据。     

Evidence of multistage late Quaternary strong earthquakes on typical segments of Longmenshan Active Fault Zone in Sichuan,China

Investigation of offset landforms and trench excavation are important means to acquire the evidence of multistage activities of active faults. Here we present the result of fault trough investigation in Beichuan County and the Pingtong Town of Pingwu County along the Longmenshan Central Fault Belt, as well as the result from trench excavation at the platform foreslope in Hanwang Town of Mianzhu County on the Longmenshan Front Range Fault Belt. These results show that at least three fault activity events, in...     

温泉逸出气体观测在长白山火山活动研究中的应用

本文回顾了流体地球化学方法在活动火山监测中的历史,重点分析了长白山火山监测站温泉逸出气体成分变化与火山活动的对应关系,得出了无论是同位素地球化学方法还是常规的温泉逸出气体检测方法,观测结果都很好地对应了火山及火山地震的活动,可以在火山喷发预报中发挥重要的作用。     

Late Holocene dune activity in the Eastern Platte River Valley, Nebraska

Large-scale dune activity in the Nebraska Sand Hills and elsewhere on the western Great Plains has been linked to prehistoric “megadroughts” that triggered the activation of regional dune fields. The effect of megadroughts on the smaller dune fields east of the Nebraska Sand Hills has never been assessed, however. This study focuses on the Duncan dune field near the confluence of the Loup and Platte rivers in eastern Nebraska. Seventeen optically stimulated luminescence age estimates were obtained and reveal two periods of dune activation that occurred between 4.4 to 3.4 ka and 0.8 to 0.5 ka. Significantly, both periods chronologically overlap large-scale dune activity identified in the Nebraska Sand Hills. Geochemical evidence indicates that the Duncan dunes received sand not only from the terrace underlying them, but also from the Loup River. These data link dune activity in the Duncan area, at least indirectly, to increased sediment supply from streams that drain the Sand Hills during megadroughts, implying the activation of the dunes occurred as an indirect response to regional megadroughts. Calculations of dune migration rates, however, argue in favor of local, drought-driven hydrologic changes as a causative factor in dune activation, in other words, a direct effect of megadroughts. Whether the impact was direct or indirect, it is highly likely that the repeated reactivation of the Duncan dunes resulted in some way from regional, large-magnitude droughts. Other paleoclimate proxies from the Great Plains tend to support this conclusion. We conclude that the megadroughts that have been identified in the Sand Hills and other Great Plains dune fields were indeed regional events with far-reaching effects.