The first estimations of soil-radon activity near faults in Central Mongolia

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• 作者：K.Zh. Seminsky^a ; ^{seminsky@crust.irk.ru} ; S. Demberel^b ; ^{demberel@rcag.ac.mn}
• 关键词：Soil-radon activity ; Fault ; Central Mongolia
• 刊名：Radiation Measurements
• 出版年：2013
• 出版时间：February, 2013
• 年：2013
• 卷：49
• 期：Complete
• 页码：19-34
• 全文大小：1999 K

文摘

Estimation of soil-radon activity, Q was first carried out for faults in Central Mongolia. Eight study sites were located in epicentral zones of Mogod (M?=?7.8; 05 January 1967) and Avdar (M?=?3.8; 22 March 2009) earthquakes, and in the vicinity of Ulaanbaatar, where small seismic events (M?=?1.0-2.5) occurred in the past few years. Profile radon surveys were conducted at fifteen faults that differ in size and geodynamic activity, yet clearly topographically manifested as scarps or straightened segments of valleys of ephemeral streams.

By applying the formalized method of processing of the survey results, it was possible to reveal radon anomalies and to establish that their shape, intensity and contrast are mainly determined by the structure of the fault zone. Due to heterogeneous permeability of fault zones, shapes and quantitative parameters of radon anomalies are variable at different faults and in individual cross-sections of one and the same fracture. Radon anomalies in Central Mongolia are diverse, yet the most frequent are the cases where (1) a radon anomaly is discontinuous in shape due to the presence of small domains with minimum values of Q; (2) a major part of the anomaly is located in one fault wall; and (3) a fault scarp is marked by a minimum value of Q. In Central Mongolia, intensities of radon anomalies, Q_max near neotectonic faults differ by more than an order of magnitude. The most intense anomaly (20,200?Bq/m³) is registered at Hustai fault in the vicinity of Ulaanbaatar, which indicates the importance of assessment of radon hazard for the capital city of Mongolia, where almost half the population of the country reside. The contrast of radon anomaly, K_Q is determined as a ratio of a maximum value of Q_max to a minimum value of Q_min outside the fault zone; it varies from 1.4 to 17.3 for faults of Central Mongolia. Faults characterized by ultra-high (K_Q?>?10), high (10?¡Ý?K_Q?>?5), increased (5?¡Ý?K_Q?>?3), medium (3?¡Ý?K_Q?>?2) and low (K_Q?¡Ü?2) radon activity are distinguished. A relative index, K_Q can be effectively applied for assessment of geodynamic activity of faults in Central Mongolia. On the one hand, it correlates with sizes and seismic potential of the studied faults; on the other hand, it significantly reduces the complicating influence of regional factors, such as radioactivity of rocks, sediment thickness, meteorological conditions of measurements, etc.

The application of K_Q, the formalized method of detection of radon anomalies, long-distance base cross-sections, and reduction of the measurement interval near faults - these key features of the profile survey are recommendable for further more accurate estimations on the basis of the first measurements of soil-radon activity in Central Mongolia.