Radon 222 measurements below 4 km as related to atmospheric convection

Summary Radon (Rn²²²) profiles were made over southwest Arizona from 300 m to 4km altitude. A temperature inversion near 2000 m and a stable radon concentration averaging 32.0 pc m^–3 at 2000 m were characteristic of morning flights. At 300 m there was a definite pattern of high radon concentrations in the early morning and lower concentrations by noon. At 760 m the radon concentration increased between the times of ascent and descent. This pattern resulted from the trapping of radon close to the ground during stable night-time conditions and its subsequent upward dispersal with solar heating. The day-to-day variation in radon concentrations at higher levels cannot be attributed to local upward transport by diffusion but must have resulted from larger scale circulations. Above 2000 m there are no conclusive differences between morning, afternoon and evening profiles. Low concentrations of radon were measured during one late evening profile when there was definite subsidence and advection of drier air into the region.     

郯庐断裂带江苏段断层气氡地球化学特征研究

为讨论郯庐断裂带江苏段断层气体氡的地球化学特征,在重岗、晓店、桥北和何庄4个地点跨断层测量了断层气氡浓度。测量结果表明:郯庐断裂带江苏段上断层气氡浓度异常衬度为2.05~5.73,且其浓度异常主要集中分布在断裂带内及附近,这与活动断裂带地震活动性有很好的一致性。     

汤阴地堑南部土壤Rn空间分布特征

为分析汤阴地堑南部土壤Rn空间分布特征,揭示其与断裂构造、岩性及沉积层厚度之间的联系,本文采用网格化布点野外流动观测方法测定了该地区380个点的土壤Rn浓度,结果表明：汤阴地堑土壤Rn浓度介于3.09—78.54 kBq/m³,背景均值为27.22 kBq/m³,异常阈值下限为48.40 kBq/m³。在空间分布上,研究区西部(以第四系等厚线50 m为界),受岩石单元和人类石料开采活动的影响,Rn浓度背景值高于东部。在西部高浓度背景影响下,Rn浓度高值异常点除沿汤西断裂带分布外,还沿断裂带外围呈斑块状分布,断裂带对气体释放的控制作用在一定程度上被掩盖。而东部地区,覆盖层较厚,Rn浓度背景值较低,部分高值异常点主要沿汤中和汤东断裂带分布,显示出构造对气体迁移的控制作用;另一部分高值异常点与第四系等厚线近似平行,呈条带分布,推测新乡—卫辉间存在一条规模较大的隐伏断裂。此外,研究区主要断裂带的Rn异常衬度表现为汤东断裂带高于汤西和汤中断裂带。结合灥研究扊区地质背景和深部孕震环境认为,该Rn异常衬度表现是汤阴地堑南部构造活动背景...     

活断层上均匀盖层中氡浓度分布的数值模拟及反演拟合

Based on the convection and diffusion mechanisms of radon migration, in this paper we deduce the two-dimensional differential equation for radon transportation in the overburden above active fault zones with an unlimited extension along the strike. Making use of the finite difference method, the radon concentration distribution in the overburden above active faults is calculated and modeled. The active fault zone parameters, such as the depth and the width of the fault zone, and the value of radon concentration, can be inverted from the measured radon concentration curve. These realize quantitative interpretation for radon concentration anomalies. The inversion results are in good agreement with the actual fault zone parameters.     

Radon anomalies on three kinds of faults in California

Radon emanation is known to be anomalously high along active faults in many parts of the world. We tested this relationship in California during July and early August 1992, using a portable radonmeter to conduct soil-air radon surveys at 5 sites across three kinds of faults: Creeping, locked, and freshly broken.Along a 350-m long survey line across a creeping segment of the San Andreas fault at Nyland Ranch in San Juan Bautista, we found anomalous radon concentrations not in the creep zone itself as determined by a creepmeter, but on the adjacent sides, 10 and 30 meters from the center line of the fault. The anomalous values were 5 times higher than the background values measured farther away from the fault. A similar radon anomaly was observed along a 420-m long survey line across a creeping segment of the Calaveras fault near 7th Street in Hollister. There, the anomalous values were about 6 to 11 times the background values and about 40 and 50 m from the center line of the fault. The double-peaked featire of the anomalies may be indicative of a relatively low gas permeability of the fault-gouge materials in the creeping zones and high permeability of fractured rocks in the adjacent shear zones.Along a 144-m survey line across the currently locked segment of the San Andreas fault at the Earthquake Trail near Olema, the radon concentration was indeed anomalously high in the fault zone, by a factor of two above background values. However, the maximum values (3 to 6 times background) again were recorded about 10 meters from the center line.Three weeks after the magnitude 7.5 Landers earthquake of 28 June 1992, we conducted a survey along a 300-m line across the earthquake fault alongside Encantado Road in the epicenter area. The radon values measured at the two main fault breaks were an order of magnitude higher than the background values. A similar result was found along a 420-m line alongside Reche Road about 1.7 km south of Encantado Road.     

鲜水河断裂带南段深部电性结构特征研究

通过对新都桥一小金剖面的大地电磁测深及重磁实测资料研究,结合区域地质资料,对鲜水河断裂带南段及邻区深部构造、壳内高导层、电性结构与历史地震的关系进行了研究.结果表明:(1)鲜水河断裂带深浅表现出不同特征,浅部是以地壳脆性-剪切带为主的断裂系统,深部是以走滑型-壳幔韧性剪切带为主的断裂系统,断裂呈花状形态,深部到达上地幔;(2)在丹巴构造带及鲜水河断裂带的中下地壳,广泛发育壳内高导层,其分布具有不均匀性,且与断裂带构造活动有关;(3)在鲜水河断裂带的走滑剪切作用下,上地壳物质发生原地重熔产生花岗岩浆是折多山花岗岩形成的主要机制;(4)鲜水河断裂带地震发生机理与塑性软弱层密切相关,受塑性软弱层拖拽作用,应力区集中在高阻体脆性介质内部靠近断层一侧,使得岩石破碎而发生地震.     

Radon variations at arrowhead and murrieta springs: Continuous and discrete measurements

Two continuous radon monitors (CRMs) have been deployed at Arrowhead Hot Springs along the San Andreas fault near San Bernardino and at Murrieta Hot Springs along the Elsinore fault. The recorded hourly and daily radon variations during 1983 are within ±5% of the mean values. The radon levels increased, however, by about 10–20% above their normal baseline levels in midyear. Several small-magnitude earthquakes (M=3.0–3.5) occurred within 20 km of the Arrowhead site near the end of the period of the radon increase.Discrete radon and helium monitoring at Arrowhead Springs since 1974 has recorded one definite precursory anomaly: a shapr increase of radon and helium (and also other dissolved gases) in 1979 by as much as 60% above their baseline levels. This anomaly was followed by the nearby Big Bear earthquake swarm (main shock,M=4.8) 45 days later. A similar increase was recorded during the first half of 1983, and it was followed by several small earthquakes (M=3.0–3.5) within 20 km of the Arrowhead site. In both cases radon and helium increased proportionally, indicating mixing between the deep-source water and the surface water at variable proportions.Comparison of radon values in gas and in liquid phases indicates that radon is not in equilibrium between the two phases but is distributed preferentially in the gas phase by a factor of 20 to 25. (Only about 5% or less of groundwater radon is in the dissolved phase.) At both sites the dissolved radon is much lower than that expected from solubility.     

郯庐断裂带宿迁段合欢路土壤氡分布特征与迁移特征的数值模拟

沿郯庐断裂带宿迁段合欢路布设土壤氡测线并对测得的数据进行分析研究,结果表明研究区域内土壤氡探测结果对断裂带位置、断层类型和特征有较好的指示性.在已知场地地质构造参数、地层岩性特征的基础上,建立土壤氡迁移模型.建立模型时识别了断裂类型和覆盖层分层特征,并讨论了断层内部结构与氡浓度取值,使模型与实际情况相等.数值模拟结果印...     

氡断层气测量在佛山西淋岗活断层探测中的应用研究

在佛山西淋岗活断层附近,垂直断层走向等距测量了断层附近载体中氡气相对含量值,得到了氡含量曲线图．分析了断层气上氡异常形态分布特征,探讨了断层气载体对氡异常形成的影响。     

Measurements of indoor radon concentrations and assessment of radiation exposure

In the past decade many international studies have established that the radioactive gas radon is responsible to a large extent for the radiation dose absorbed by the population. Consequently the Swiss Federal Health Office started and sponsored a research program called RAPROS (Radon Programm Schweiz, 1987–1991) to assess the relevant aspects of radon exposure in Switzerland.The average indoor radon concentration in Swiss living rooms is about 60–70 Bq m⁻³, this corresponds to an annual dose of about 2.2 mSv, but values largely exceeding 1000 Bq m⁻³ were also found. Often very strong temporal fluctuations of indoor radon concentrations were measured.The ground directly underneath buildings is the main radon source of indoor radon. The material properties that influence the radon production and transport in soils are: radium content, emanating coefficient and soil gas permeability; among them only the last one can vary over many orders of magnitude. The permeability is consequently the decisive factor that enables radon transport in the subsurface. To characterize the radon potential of soils a radon availability index (rav) was introduced.Our investigations have also shown that in karst systems the radon concentration in the air is often increased to 10–100 times higher than in buildings. This radon-charged air is able to travel over considerable distances through faults and cavities in the underground and reach living rooms built over karstified areas.     

刘家堡活动断层土壤气氡、 汞地球化学特征

应用FD-3017RaA测氡仪和JM-4数字金膜测汞仪在兰州市进行了野外现场勘察, 结果表明: ① 刘家堡断层土壤气氡、 汞具有明显的异常显示。 与气氡相比, 土壤气汞具有更好的指示性, 与断层位置有很好的对应关系; ②土壤气氡、 汞的典型异常形态为低-较高-高-较高-低的峰值形态。 单点异常大多数为观测中的干扰因素造成; ③ 在断层带上方氡、 汞的峰值异常一般比背景值高出2倍以上, 且具有成组特征, 即在断层带上方超过背景值2倍以上的点2个以上。 根据断层带土壤气氡、 汞的变化特征, 确定了刘家堡活动断层在不同区段的具体位置。 探讨了利用土壤气氡、 汞浓度形态变化特征判断活断层性质及产状的可能性。     

夏垫隐伏断裂土壤气氡分布特征的初步研究

通过横切夏垫隐伏断裂的土壤气氡剖面测量，作者发现，土壤气氡的正异常区位于该隐伏断裂上盘的地表投影区内，断裂附近的土壤气氡等值线分布表明，沿夏垫隐伏断裂，气氡等值线有一个明显的梯度带。     

氡迁移的接力传递作用

在扩散和对流等作用的基础上，提出了用于解释氡法探寻深部矿藏、预报地震和研究地球动力学带等方面的氡迁移的接力传递作用．这种作用可能是镭传氡和氡传氡，也可能是借助于其它的物质或自然力来传递，传递方式有二棒接力和多棒接力．扩散和对流等10多种作用．一般地说，只能使氡气作短距离的迁移，而接力传递作用则可以解释氡作长距离的迁移．     

基于形变观测分析2011年日本9.0级地震与断层运动间关系

2011年3月11日日本发生9.0级地震,本文以此次地震的震间、同震和震后形变观测为约束,依据不同时段断层运动空间分布特征分析日本海沟地区强震与断层运动间关系.震间日本海沟地区,断层运动闭锁线深度约为60km,闭锁线以上从深到浅依次为断层运动强闭锁段、无震滑移段和弱闭锁段.由同震位错反演结果,2011年日本9.0级地震同震存在深浅两个滑移极值区,同震较浅的滑移极值区(同震位错量10~50m,深度小于30km)震间为断层弱闭锁段;同震较深的滑移极值区(同震位错量10~20m,深度在40km左右)震间为断层强闭锁段;而在两者之间的过渡带同震位错相对较小,震间断层运动表现为无震滑移.震后初期断层运动主要分布在在闭锁线以上的同震较深滑移极值区,而同震较浅的滑移极值区能量释放比较彻底,断层震后余滑量相对较小.依据本文同震和震间断层运动反演结果,震间强闭锁段积累10m同震位错需要100多年时间,与该区域历史上7级地震活动复发周期相当;震间弱闭锁段积累30~50m同震位错约需要300~600年时间,与相关研究给出的日本海沟9级左右地震复发周期比较一致.在实际孕震能力判定的工作中,由于不同性质的断层段在同震过程中会表现更多的组合形式,断层发震能力判定结果存在更多的不确定性,但利用区域形变观测等资料给出震间断层运动特征的研究工作对于断层强震发震能力的判定具有非常重要的实际意义.     

福州市隐伏断层地球化学试验探测及研究

在城市环境中进行隐伏断层地球化学探测试验是一次新的尝试。试验探测内容包括 :不同地球化学测项 (土壤气汞和土汞、土壤气氡等 )、不同类型测氡仪器 (FD - 12 5 ,FD - 30 17RaA)、不同探测场地 (稻田、菜地、林区、道路、回填土和市区街道绿化带等 )。地球化学与浅层地震勘探结果的比较表明 ,2类异常点的对应率约为 70 % ,表明地球化学方法在福州市环境下的隐伏断层探测中是一种有效的方法 ;地球化学“伪异常”出现的可能部位是小桥边、废弃建筑物地基、路边垃圾堆放地等     

Integrated Deep Soil N and Groundwater Isotope Investigation of N Sources Captured by Municipal Wells

Identification of major nitrate sources that adversely impact groundwater quality in municipal well capture zones in areas of emerging nitrate contamination is essential to minimize leaching and prevent exceedance of the nitrate drinking water standard. Vertical profiles of nitrate leachate in deep soils provide an estimate of the amount of nitrate in transit beneath irrigated, row-cropped fields; depths of peak leachate; and the approximate rate of downward movement. Profiles of pore-water soil-nitrate concentrations in thick 60-feet (~18 m), fine-textured soils near Hastings, Nebraska clearly indicate that considerably more nitrate leached beneath furrow-irrigated than center-pivot irrigated fields. Peak leaching appeared to correlate with recorded periods of poor weather conditions during some growing seasons and may best be controlled by “spoon feeding” fertilizer to the crop through the sprinkler irrigation system at times of nutrient need. The presence of trace levels of atrazine and deethylatrazine to 60 feet (18 m) in core samples indicates that larger, more complex anthropogenic molecules also leach through the fine-textured soils. The light δ¹⁵N_NO3 values in the surficial groundwater beneath fertilized and irrigated cropland indicate that ammonium fertilizer is a major N source and suggest that the natural soil-N contribution is negligible. δ¹⁵N_NO3 values were most enriched in irrigation wells located within municipal well capture zones downgradient of a large feedlot. Dual isotope method (DIM) δ¹⁵N_NO3 and δ¹⁸O_NO3 values suggest that the Hastings’ municipal wells farther downgradient are contaminated with a mixture of nitrate from manure and commercial ammonium-based fertilizer. DIM values indicate an absence of denitrification, which has implications for long-term management of the water resources.     

A New Zealand test of the track-etch® method of prospecting for geothermal steam

The Track Etch® system for radon detection was evaluated as a geothermal exploration technique in a known geothermal resource area in New Zealand called the Craters of the Moon (previously known as “Karapiti”). Very strong radon anomalies spaced along mapped fault traces were detected using 60-m sample spacings. Such radon anomalies may indicate good areas to drill for steam. The anomalies detected in these tests were located inside a larger area known to have above-back-ground concentrations of radon and thought to be a generally favourable area for finding shallow steam. Track Etch® radon cups with an improved type of detector were found to be usable in ground temperatures as high as 60°C. There was no direct correlation of radon concentrations with resistivity measurements, but a moderate correlation with near-surface temperature measurements. Varying vegetation cover had no significant effect on the results but there was an apparent correlation with superficial pumice deposits. It is concluded from the tests that the Track Etch method shows promise in vapour-dominated areas for improving drill-hole siting and thus reducing the economic loss of drilling non-productive holes.     

Controlling factors of gullying in the Maracujá Catchment,southeastern Brazil

Hundreds of gullies (‘voçorocas’) of huge dimensions (up to 400–500 m long, 150 m wide and 50 m deep) are very common in the small Maracujá Catchment in southeastern Brazil. These erosional features, which occur with an uneven intensity throughout the area, started due to bad soil management practices at the beginning of European settlement, at the end of the 17th century, and nowadays are still evolving, but at a slower rate. As surface soils are usually very resistant to erosion, the outcrop of the more erodible basement saprolites seems to be an essential condition for their beginning. An analysis of well known erosion controlling factors was performed, aiming to explain the beginning and evolution of these gullies and to understand the reasons for their spatial distribution. Data shows that geology and, mainly, geomorphology are the main controlling factors, since gullies tend to be concentrated in basement rock areas with lower relief (domain 2) of Maracujá Catchment, mainly at the fringes of broad and flat interfluves. At the detailed scale (1:10 000), gullies are more common in amphitheatre‐like headwater hollows that frequently represent upper Quaternary gullies (paleogullies), which demonstrate the recurrence of channel erosion. So, gullies occur in areas of thicker saprolites (domain 2), in places with a natural concentration of surface and underground water (hollows). Saprolites of the preserved, non‐eroded hollows are usually pressurized (confined aquifer) due to a thick seal of Quaternary clay layer, in a similar configuration to the ones found in hollows of mass movement (mudflow) sites in southeastern Brazil. Therefore, the erosion of the resistant soils by human activities, such as road cuts and trenches (‘valos’), or their mobilization by mudflow movements, seem to be likely mechanisms of gullying initiation. Afterwards, gullies evolve by a combination of surface and underground processes, such as wash and tunnel erosion and falls and slumps of gully walls. Copyright © 2005 John Wiley & Sons, Ltd.     

祁连山断裂带中东段断层土壤气氡浓度强度时空分布特征及其地震危险性分析

基于祁连山断裂带中东段9个观测点2016—2021年的土壤气体氡浓度观测数据,深入分析其浓度强度时空分布特征。同时结合历史大震背景、现今地震活动与断裂带滑动速率的对比分析,从地球化学的角度对祁连山断裂带中东段进行地震危险区段判定。研究表明：祁连山断裂中东段土壤气体氡浓度强度的空间分布特征为东强西弱,其时间序列变化特征总体呈下降趋势;断层土壤气氡浓度强度的空间分布特征、历史及现今地震活动和断裂滑动速率具有较好的耦合性。研究结论可以提供研究区深部地下流体活动的证据,对进一步研究追踪未来可能发生地震的断层和活动段具有重要意义。     

天津地区断层气方法应用中的两个问题

运用海河断裂、 沧东断裂、 天津北断裂和天津南断裂断层气测量结果, 同时结合人工地震探测结果, 讨论了土壤气氡异常位置与断层上断点位置的关系和土壤氡背景场与背景值的问题。 研究结果表明, 覆盖层的厚度对土壤气氡异常的位置存在一定影响, 覆盖浅的断层, 断层气异常一般在断层上断点的上方; 覆盖厚的断层, 断层气异常往往与断层位置不一致, 至少存在60 m左右的误差, 说明断层气异常存在偏离断层的情况。 从偏移距离以及异常位于断层的上盘或下盘上看, 未发现有统计上的关系。 在土壤气氡测量结果的异常确定上, 以每条测线的相对高值判定异常为宜, 不宜使用统一的背景场来确定异常。