Contrasting radon background levels in volcanic settings: clues from 220Rn activity concentrations measured during long-term deformation experiments

To better understand the mechanisms leading to different radon background levels in volcanic settings, we have performed two long-term deformation experiments of 16 days using a real-time setup that enables us to monitor any variation of radon activity concentration during rock compression. Our measurements demonstrate that, in the case of highly porous volcanic rocks, the emanating power of the substrate changes as a function of the volcanic stress conditions. Constant magmatic pressures, such as those observed during dike intrusions and hydrothermal fluid injections, can result in pervasive pore collapse that is mirrored by a significant radon decrease until a constant emanation is achieved. Conversely, repeated cycles of stress due to, for example, volcano inflation/deflation cycles, cause a progressive radon increase a few days (but even weeks and months) before rupture. After rock failure, however, the formation of new emanation surfaces leads to a substantial increase of the radon signal. Our results suggest that surface deformation in tectonic and volcanic settings, such as inflation/deflation or constant magmatic pressures, have important repercussions on the emanating power of volcanic substrates.     

Radon emanation as an indicator of the intensity of Intergeospheric interactions at the Earth’s crust-atmosphere interface

The results of measurements of the volumetric activity of subsurface radon Rare given for several sections of the Earth’s crust located within the central part of the East European Platform. The influence of tectonic structures on the spatial zonality of radon emanation and the intensity of its temporal variations is shown. The temporal variations in radon emanation are characterized by periodicity with periods of approximately a day, as well as of 4, 14, and 29 days, and, as correlation analysis shows, they are determined by the cyclic recurrence of tidal deformations and by cyclonic processes in the atmosphere. The high correlation of the mean values of the volumetric activity of subsurface radon with the value of atmospheric pressure is established. The dependence of the volumetric activity of subsurface radon and its temporal variations on the depth within the range of depths 0.8–11.5 m is determined. As a result of laboratory experiments, the nonlinear nature of the dependence of radon emanation on the frequency of vibration action is established. For granites, the intensity of radon emanation is maximal at frequencies of 16 and 32 Hz. The results of complex measurements of the microseismic background and the volumetric activity of subsurface radon carried out in the region of the Nelidovo-Ryazan tectonic structure demonstrate the high correlation between the volumetric activity of subsurface radon and the relative amplitude of the quasi-monochromatic component of the microseismic background with a peak frequency of 16.5 Hz.     

水氡仪器标定异常原因浅析

2008年8月福建省地震局水化学中心实验站对新购置的水氡仪器进行标定,标定结果出现异常：全部闪烁室K值超出《地震水文地球化学观测技术规范》所要求的取值范围,但每个闪烁室多次标定的K值的相对偏差基本小于5％,说明虽然K值超出要求,但是固体氡气源装置上标称氡射气剂量分配值是稳定的。造成标定结果异常的可能原因主要有,标定过程出现漏气,新仪器选择的各项指标有误,固体氡气源故障。更换干燥剂、橡皮管,检查每一个接口,以及闪烁室的密封性能和真空泵的抽真空性能,重新检查仪器状态均已正常后,用现用的两套仪器进行标定,以检验是否因新仪器选择的各项指标有误造成标定结果异常。两次标定结果类似,分析认为,可能是固体氡气源故障,虽然在这次标定中,固体氡气源装置上标称氡射气剂量分配值是稳定的,但可能其含量较以前发生了变化。     

Role of microstructure in clay emanation

The influence of clay microstructure on radon emanation has been studied based on the analysis of literary data and direct measurements of the emanation coefficient of different types of clay rocks. Experiments have shown that modern and Holocene clay and silt with a cellular microstructure have the highest emanation coefficient (more than 60%). The majority of clay rocks transformed by diagenesis (showing either matrix or turbulent microstructure), have the emanation coefficient of about 50%. The emanation coefficients of lithified clay and argillite (laminar microstructure) do not exceed 10%. Thus, the emanation capacity of clay depends on clay microstructure and regularly decreases in the following row: cellular > matrix or turbulent > laminar microstructure.     

Indoor Radon Radioactivity at the University of Brunei Darussalam

— Indoor radon radioactivity in the rooms on the ground floor and first floor of the Physics Department, Faculty of Science, Universiti Brunei Darussalam was measured using a system that consists of an air filter pump, ZnS detector, photomultiplier tube and counter. Ground floor rooms' radon radioactivity was found to be about three times higher than that of the first floor. The maximum ground floor indoor radioactivity is only 0.39 Bqm^?3, a value relatively low and safe compared to the mean outdoor radon concentration of 1.41 Bqm^?3 measured (HU and TAN, 2000). The main source of radon emanation originates from the ground soil rather than the building materials.     

Anomalous radon emanation at local and regional distances preceding earthquakes in the New Madrid seismic zone and adjacent areas of the central mid-continent of North America, 1981–84

Anomalous soil-radon activity, including several spike-like surges over periods of 5, 2, and 2 1/2 months, and a year-long declining trend, preceded the most significant earthquakes of the central mid-continental region of North America during 1981 and early 1984. The 5-month period of erratic weekly radon activity, February–June 1981, was followed by a tremor of magnitudeM=4.0, 40 km from the monitoring site in the New Madrid seismic zone. An unusual earthquake swarm in central Arkansas, 160 km from the New Madrid seismic zone and 230 km from the monitoring site in the seismic zone, began in January 1982, shortly after a year-long declining trend in anomalous radon emanation. Earthquakes of magnitudes 4.5, 4.1, and 4.0 occurred at the swarm's outset in early 1982, fitting a pattern anticipated for the New Madrid seismic zone on the basis of the radon activity. Two periods of coincident peak radon emanation have since been observed in the Arkansas and New Madrid seismic regions, as have synchronous seismic pulses for the two separate areas.Two more recent periods of highly erratic soil-radon emanation, March–May 1983 and November–January 1984, were followed by a 4.3 earthquake in southwestern Illinois on 15 may 1983, and 3.5–3.6 tremors and swarm activity in the New Madrid seismic zone in late January and mid-February 1984. Prior to the 4.3 event, radon peaked at three widely separated monitoring sites 1–3 weeks before the tremor at distances of 120, 225, and 320 km from the epicentral region, the station at 225 km, in the New Madrid seismic zone, recording the longest period of anomalous radon activity. As for the recent 3.5–3.6 tremors of 1984, seismic activity of this magnitude had been anticipated for January or February on the basis of the amplitude of the November radon anomaly.These observations provide further evidence of (a) the existence of soil-radon anomalies precursory to the large earthquakes in this intraplate region, (b) the utility of such anomalies in anticipating events of small to moderate magnitudes for the region, and (c) the occurrence of regional-scale strain events prior to some of the larger mid-continental earthquakes.A very recent radon anomaly, the strongest yet to be detected in the seven years of monitoring in the mid-continental region, occurred in the New Madrid seismic zone from mid-February through mid-June 1984. A 4.0 earthquake occurred one month after a peak in the radon activity. The amplitude and duration of the anomaly suggest that a significant change in the state of stress or strain may have occurred in the mid-continental region during 1984.     

Radon anomalies and volcanic eruptions

A well-documented case of ²²²Rn anomaly preceding the eruptive activity of Karymsky volcano (Kamchatka) was recently reported in the literature. Stimulated by this example, we have attempted to utilize the available data on radon emanation from rocks, its solubility, and its circulation in waters to discuss how a ²²²Rn anomaly can be produced by magma approaching the surface. It is shown that the most likely process of radon release is the flushing of gases through pore fluids. Heating of extensive fracture surfaces by high-temperature gases may also be important. In order to survive in detectable amounts after moving distances greater than a few meters, radon must be transported by fast-moving fluids, such as those rising toward the surface through a fracture or in the ascending limbs of fluids convecting in very porous rocks under high temperature gradients. The pattern observed at Karymsky volcano is interpreted on the basis of these relations.     

Variations in radon activity in the crustal fault zones: Spatial characteristics

The data of the profile gas emanation survey conducted on three spatial scales in separate regions of the Mongolia-Baikal seismic belt are generalized to establish the regularities of the spatially heterogeneous distribution of soil radon activity above the active faults in the Earth’s crust. It is shown that the shapes, sizes, and contrast of the near-fault radon anomalies are complicated by erosion and weathering; however, the critical role in their formation is played by the structural-geological controls, which determine the internal structure and recent activity of the fault zones. As a consequence, the cross-fault shape of the studied radon anomalies is vitally controlled by four structural situations, which correspond to the combinations of the structural type of the fault (localized/distributed) and the presence/absence of the fine filler material in the zone controlled by the fault. The cross-fault dimension of the emanation anomaly is commensurate or slightly larger than the width of the fault zone comprising all the fractures and joints associated with the formation of the main fault, which, due to the low permeability of the tectonites, is in most cases marked by the lowest concentration of soil radon. The contrast of the emanation anomalies, which we suggest to estimate in terms of a relative parameter K _Q , gravitates to certain levels of this parameter. This provides the basis for distinguishing five groups of the fault zones with low (K _Q ≤ 2), moderate (2 < K _Q ≤ 3), increased (3 < K _Q ≤ 5), high (5 < K _Q ≤ 10), and ultrahigh (K _Q > 10) radon activity. The previous studies show that for increasing the efficiency of the emanation survey in the fault zones, it is advisable to set up long profiles, reduce the measurement step in the vicinities of the main faults, specify the threshold of identifying the anomalies at the arithmetic mean level over the profile, and use the relative parameter K _Q for comparing and estimating the faults in terms of the intensity of their radon activity.     

氡(Rn)射气测量在胜利油田隐伏断裂研究中的应用

土壤氡(Rn)射气测量是探测隐伏断裂的存在,判定断裂的位置、走向、倾向的一种有效手段。通过在胜利油田进行的氡射气探测并结合其它勘探手段,发现该区主要的隐伏潘动断裂有无棣—益都断裂、胜北断裂和埕子口断裂。其中,无棣—益都断裂活动性最强。     

Seismotectonic zones demarcation in the Shillong Plateau using the microearthquakes and radon emanation rate

The Shillong Plateau signifies the intense tectonic processes that the region has experienced during the Tertiary Indo-Tibetan and Indo-Burman collisions. An attempt has been made to study the microearthquake and radon emanation rate to understand and identify the seismotectonic zones.     

牡丹江地震台水氡观测系统改造

针对牡丹江台FD-125射气仪氡本底过大的问题,分析本底大的原因,对原有观测系统进行改造,收到良好效果。     

Measurements of radon flux and soil-gas radon concentration along the Main Central Thrust, Garhwal Himalaya, using SRM and RAD7 detectors

Radon in the Earth’s crust or soil matrix is free to move only if its atoms find their way into pores or capillaries of the matrix. ²²²Rn atoms from solid mineral grains get into air, filling pores through emanation process. Then ²²²Rn enters into the atmosphere from air-filled pores by exhalation process. The estimation of radon flux from soil surface is an important parameter for determining the source term for radon concentration modeling. In the present investigation, radon fluxes and soil-gas radon concentration have been measured along and around the Main Central Thrust (MCT) in Uttarkashi district of Garhwal Himalaya, India, by using Scintillation Radon Monitor (SRM) and RAD7 devices, respectively. The soil radon gas concentration measured by RAD7 with soil probe at the constant depth was found to vary from 12 ± 3 to 2330 ± 48 Bq·m^?3 with geometrical mean value of 302 ± 84 Bq·m^?3. Th significance of this work is its usefulness from radiation protection point of view.     

Ground variation of radon 222 for location of hidden structural features. Example of the south of France (Alpes Maritimes)

We report two examples from the south of the French Alps, showing that radon emanation monitored by alpha-sensitive film may be used to locate certain discrete structural features revealed in data collected by remote sensing from a satellite. The variations observed in our data, over a period of several months, are in accordance with atmospheric changes and might correlate with local seismic activity when the detectors are located directly above structural fractures and the magnitude of the seismic event is greater than 2.     

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.     

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...     

Impulsive radon emanation on a creeping segment of the San Andreas fault,California

Radon emanation was continuously monitored for several months at two locations along a creeping segment of the San Andreas fault in central California. The recorded emanations showed several impulsive increases that lasted as much as five hours with amplitudes considerably larger than meteorologically induced diurnal variations. Some of the radon increases were accompanied or followed by earthquakes or fault-creep events. They were possibly the result of some sudden outbursts of relatively radon-rich ground gas, sometimes triggered by crustal deformation or vibration.     

Variations of electric resistance and H2 and Rn emissions of concrete blocks under increasing uniaxial compression

Electric resistance and emissions of hydrogen and radon isotopes of concrete (which is somewhat similar to fault-zone materials) under increasing uniaxial compression were continuously monitored to check whether they show any pre- and post-failure changes that may correspond to similar changes reported for earthquakes. The results show that all these parameters generally begin to increase when the applied stresses reach 20% to 90% of the corresponding failure stresses, probably due to the occurrence and growth of dilatant microcracks in the specimens. The prefailure changes have different patterns for different specimens, probably because of differences in spatial and temporal distributions of the microcracks. The resistance shows large co-failure increases, and the gas emissions show large post-failure increases. The post-failure increase of radon persists longer and stays at a higher level than that of hydrogen, suggesting a difference in the emission mechanisms for these two kinds of gases. The H₂ increase may be mainly due to chemical reaction at the crack surfaces while they are fresh, whereas the Rn increases may be mainly the result of the increased emanation area of such surfaces. The results suggest that monitoring of resistivity and gas emissions may be useful for predicting earthquakes and failures of concrete structures.     

Radon-222 as a tracer for mixing in the water column and benthic exchange in the southern California borderland

The concentrations of²²²Rn and²²⁶Ra in the water column and in the sediments of Santa Barbara and San Nicolas Basins have been measured semi-annually over the last four years. Approximately one-third of excess radon profiles obtained in the water column in these basins can be adequately fit with a one-dimensional eddy diffusion-decay model. Exponential profiles in the center of San Nicolas Basin yield a vertical eddy diffusivity of 26±16 cm²/s and 3.4±1.0 cm²/s for Santa Barbara Basin. The application of a two-dimensional eddy diffusion-decay model to profiles obtained in the center and on the margins of San Nicolas Basin produces a better fit than is found using a one-dimensional vertical eddy diffusivity. The two-dimensional model for San Nicolas Basin predicts a vertical eddy diffusivity of 17 cm²/s and a horizontal eddy diffusivity of 10⁵ cm²/s. These values are in reasonable agreement with those predicted from the vertical buoyancy gradient and the horizontal length scale.The vertically integrated radon excess (standing crop) in the water column of Santa Barbara Basin averages 53±23 atoms/m² s. This is in good agreement with the flux across the sediment-water interface of 60±15 atoms/m² s, calculated by measuring radon emanation in the sediments as a function of depth and applying a molecular diffusion-reaction model. Hence, one-dimensional molecular diffusion accurately predicts the flux of radon from the laminated Santa Barbara Basin sediments. In San Nicolas Basin the integrated radon excess in the water column is 376±143 atoms/m² s, but the diffusive randon flux from San Nicolas Basin sediments averages only 190±53 atoms/m² s. This descrepancy indicates that a non-diffusive process, probably macrofaunal irrigation, supplies much of the flux of radon from San Nicolas Basin sediments.     

Radioactive elements in sediments and altered rocks of the Kikhpinych long-lived volcanic center

Data on the concentration of radioactive elements in mineral sediments and hydrothermally altered rocks of the long-lived Kikhpinych volcanic center are presented. High concentrations of uranium (up to 31 g/t) and thorium (up to 46 g/t) relative to the average values for the dacites of Kamchatka and the Uzon-Geyser depression are found in white kaolinite clays of mud pots and in dacites of the Yuzhnoe Kikhpinych thermal field transformed into kaolinite clays. In this field and in the Severnoe thermal field (in the crater of Staryi Kikhpinych Volcano) high values of volume radon activity (VA Rn > 1000 kBq/m³) were recorded in subsoil air. These high concentrations of uranium and thorium in fresh mineral sediments and anomalous values of VA Rn in subsoil air of hydrothermally altered rocks are considered to have resulted from the mass transfer of radioactive elements by fluid flows of the hydrothermal system.     

Dynamic processes in the system of interacting geospheres at the Earth’s crust-atmosphere boundary

Results of various instrumental observations of geodynamic processes in the Earth’s crust and geophysical fields at the crust-atmosphere boundary in the Oka area of the Nelidovo-Ryazan tectonic structure and adjacent fractures and in the zone of the Gornyi Altai earthquake of September 27, 2003, are presented. The correlations between the geophysical fields are determined from the results of processing and analysis of microseismic vibrations, the emanation field of natural radon, and variations in the electric field in ground and the magnetic field in the surface atmospheric layer. Tidal deformations of the crust were considered as external effects enhancing the interactions between the geospheres. It is noted that tectonic faults determining the block structure of the crust are recognizable as anomalous variations in the geophysical fields and their high cross-correlation.