Low-density geochemical mapping in Hungary

Guidelines for a low-density geochemical survey were described in 1990 by the Western European Geological Surveys. A low-density geochemical survey of Hungary was carried out in 1991–1995. The results are useful for future surveys and for the IGCP 360 project ‘Global Geochemical Baseline’. In regions with well-developed drainage systems in Hungary, 196 catchment basins of approx. 400 km² were delineated and flood-plain deposits sampled at their outlets. The samples were taken from 0 to 10 cm and from 50 to 60 cm depths. Samples were analysed by ICP-AES and AAS techniques in two laboratories. A Geochemical Atlas of Hungary is in preparation that will show the distribution of 25 elements in the two sampled layers. Maps for the lower layer represent regional geochemical baseline values and a geochemical subdivision of the country (maps showing the distribution of element associations) was made on the basis of factor variables. Maps constructed from the data of the upper sampling level show us the present state of contamination of the surface. The results of this survey have contributed to the establishment of guidance values for soils prepared by the Hungarian Ministry of the Environment in 1995. Safe levels were established for As, Cd, Cr, Cu, Hg, Pb and Zn and regional environmental loads plotted. Differences between the median values of the two levels are generally small. However, the concentrations of certain elements like P, Pb and S are significantly greater in the upper layer reflecting contamination from agriculture. In certain regions, the rate of sedimentation was fairly fast such that the environmental effects of ore mining in Transylvania and southern Slovakia as well as those of heavy industry in northern Hungary can be observed in samples from the lower level. The main factor controlling the geochemical pattern in Hungary is the predominance of young (Pleistocene or Miocene) clastic sediments at the surface. Approx. 90% of the surface is covered by these young sediments. This kind of survey has the disadvantage of not providing enough contrast to differentiate geologically dissimilar areas but it has the advantage to provide regional surface background geochemical data and it helps to outline areas of possible surface contamination. Based on the results of this survey we conclude that it would be much better to sample smaller, but geologically homogeneous areas in mountainous terrain to obtain data characteristic of the geochemical background of lithologic units. This approach would mean a sampling density of a few tens of km²/sample for hilly areas, and a few hundred km²/sample for lowland areas.     

Nitrate temporal and spatial patterns in 12 water-supply wells, Yucatan, Mexico

 The nitrate concentration in 12 water-supply wells were monitored for the period April 1992 to March 1993. Each water-supply well was sampled once a month. The nitrate concentrations in the 12 wells ranged from 7 to 156 mg/l. Two water-supply wells (Chacsinkin and Peto) showed concentrations that reached 3.5 times the maximum permissible limit for the Drinking Water Standard (45 mg/l). A third water-supply well (Akil) exceeds the norm for 7 out of 12 months. The use of nitrogen-rich fertilizers are responsible for high nitrate concentrations in groundwater in the southern part of Yucatan, Mexico where intensive agricultural practices exist. Received: 14 December 1999 · Accepted: 2 May 2000     

Hydrogeological and geotechnical assessments of the Kadifekale landslide area, İzmir, Turkey

 The study area is located in the south of İzmir city centre in an area built without planning permission or any overall city plan. In this area, a number of mass movements occurred in the past and the region is still an active landslide field at present. The real sliding factor is geological structure, which is made up of hard volcanic rocks overlying soft Neogene clayey soils, and forms a typical structure prone to sliding. Unplanned human activities change the hydrogeological and geotechnical stabilities of the geological formations in a negative way. Rain and water leaking either directly from the mains or septic holes infiltrate into the ground and act as one of the factors in causing landslides. It is clearly shown that the irregular urbanization in and around Kadifekale is one of the factors contributing to the landslides in the area. To prevent the occurrence of landslides in the study area an effective surface and under ground drainage should be established. Rain and wastewater should be removed from the area by separate systems. Slopes should be reduced, water-loving trees should be planted and construction of high rise buildings should be avoided. Received: 12 December 1997 · Accepted: 4 April 2000     

Damage to Residential Fills in the 1995 Hanshin-Awaji Earthquake

This paper summarizes the features of ground damage toresidential fills due to the 1995 Hyogo-ken NanbuEarthquake in Japan. Many residential lands sufferedground damage to various extents in the earthquakeevent. Permanent deformation took place ingently-sloping residential fills. Some slopes asgentle as four degrees exhibited landslide-likedownward movements from dozens to hundreds ofcentimeters, so on. It is suggested that liquefactionmight be a dominant factor for displacements ingently-inclined residential fills.     

Regional assessment and mapping of groundwater vulnerability to contamination

In many regions the use of groundwater for water supply is limited by the increase in contamination of aquifers. The problem of contamination requires the development of new approaches in assessing areas in which groundwater is vulnerable to contamination. A brief analysis of the present day level of methods for regional evaluation and mapping of areas in which groundwater is vulnerable is presented.     

Magma movements in Etna volcano associated with the major 1991–1993 lava eruption: evidence from gravity and deformation

The 1991–1993 eruption was probably the largest on Mt. Etna for 300 years. Since then the volcano has entered an unusually quiescent period. A comprehensive record of gravity and ground deformation changes presented here bracket this eruption and give valuable insight into magma movements before, during and after the eruption. The gravity and deformation changes observed before the eruption (1990–1991) record the intrusion of magma into the summit feeder and the SSE-trending fracture system which had recently been active in 1978, 1979, 1983 and 1989, creating the feeder dyke for the 1991–1993 eruption. In the summit region gravity changes between 1992 and 1993 (spanning the end of the eruption) reflect the withdrawal of magma from the conduit followed more recently (1993–1994) by the re-filling of magma in the conduit up to pre-eruption levels. In contrast, in the vicinity of the fracture zone, gravity has remained at the 1991–1992 level, indicating that no withdrawal has occurred here. Rather, magma has solidified in the fracture system and sealed it such that the 1993–1994 increase in magma level in the conduit was not accompanied by further intrusion into the flanks. Mass calculations suggest that a volume of at least 10⁷ m³ of magma has solidified within the southeastern flank of the volcano.     

地倾斜观测资料的归算

本文针对我国地倾斜观测仪器设置的实情，推导出由任意两方向设置的倾斜仪观测资料计算地倾斜角及其倾斜方位角有的通用公式，以及归算至南北、东西方位的公式。用本文的公式对泰安台两种类型倾斜仪观测进行了归算，归算后其倾斜固体潮曲线同就变化，相关性明显增强。对大同－阳讥Ｍｓ－６．１地震前的倾斜异常资料也进行了归算，归算后异常也比较明显。最后，作用还对我国地倾斜观测资料的归算工作提出了具体意见。     

地电阻率瞬时突变序列变化与临震预报

本文采用断裂力学观点，分析研究了一些临震预报实验结果与地电实际观测资料。发现在强震与部分中强震前，震中附近的台站，除能预测到有关地震的地电阻率日突变序列的短期异常变化外，在瞬时突变序上还能看到临震前明显的突变现象，还是震前三个月里的最大瞬时突变，从它的出现至发震所需的时间，将随震中距的减少而缩短，且与震级有关，对于强震多集中出现在震前一个月内，中强震为十天内，并有由外围向震中收缩的趋势，其平均收缩     

M-LDARS观测的北京地区云地闪特征分析

1991年夏,我们利用自制的单站闪电探测及定位系统(M—LDARS),在北京地区进行了对比实验,并对所记录的地闪回击信号作了分析。本文提出了我们得到的北京地区云地闪回击信号的峰值时间、半峰时间、峰值电流以及电流上升率的统计分布和频谱特征的典型结果,并与国内外同类观测的结果进行了对比。     

中国地震倾斜潮观测台网

系统论述了中国地震倾斜潮观测台网利用地倾斜及其潮汐监测预报地震的科学思路、台网特征、观测精度、映震效能等。重点总结了建网中切合国情、台情的中国独特经验;对第一代、新一代台网记录倾斜同震阶跃信息与前兆异常现象的能力作了对比;还讨论了台网的应用前景。