Spatial Variations of Soil Gas Geochemistry in the Tangshan Area of Northern China

Abstract

The concentrations of Hg, Rn, H 2 , He and CO 2 in soil gases at 756 sites were measured in the Tangshan area where M s 7.8 earthquake occurred in 1976 and is characterized by complex tectonic structures and high seismic hazard. The results showed that, spatial variations of the gaseous anomalies, especially hydrogen and helium have spatial congruence along the tectonic lines, which can be attributed to their deep sources and the migration paths formed by the faults. A better congruence of radon and carbon dioxide is highlighted which indicates that carbon dioxide acts as the carrier gas for radon in this area. Two geochemical anomaly zones of soil gas were found in the area wherein all the studied gases exhibited anomalies or high values, related to the faults and earthquakes.

Evidence of Multiple Sources of Soil Gas in the Tangshan Fault Zone, North China

“…General overviews of the geochemical, structural, and seismic features in tectonically active areas have shown some evidence of correlation between soil gas geochemistry anomalies and tectonic activities, and soil gas discharge through fault and fracture in the active fault zones can be enhanced by fault and earthquake activity (Wakita et al, 1980;Toutain et al, 1992; [8][9][10][11]). As such, analyzing the origins and geochemical variations of soil gas in the seismically active areas could be a potential way to study faults and seismic activity [12][13][14]. At present, soil gas concentration and flux surveys along active fault zones have been widely undertaken for earthquake research and prediction (Caracausi et al, 2003; [11,15]).…”

Rn and CO<sub>2</sub> geochemistry of soil gas across the active fault zones in the capital area of China

“…Soil gas CO 2 sampled from the sampling device was immediately injected into the GC via a glass syringe. The detection limit of CO 2 is 2 ppm, calibrated by standard gas (Li et al, , 2013.…”

“…Furthermore, as crustal thickness in Yanqing-Huailai Basin is larger than at the other two regions , the soil gas at the DY and LY profiles would contain less deep gas of Rn for the decay of 222 Rn to 218 Po with migration. Compared with the Sanhe-Pinggu region, lower values of Rn in Tangshan are affected by the high soil moisture attributed to the low ground water level (Li et al, 2013). The emanation coefficient of Rn will decrease when the moisture content of soil increases and reaches saturated conditions (Menetrez and Mosley, 1996).…”

“…Li et al (2009) discussed the geochemical characteristics of soil gases in Yanqing-Huailai Basin and found that the concentrations of Rn, CO 2 , He, H 2 and Hg were higher in the east of the basin than the west, which may be related to the tectonic activity of the area. Li et al (2013) investigated the concentrations of soil gases (Hg, Rn, H 2 , He and CO 2 ) in the Tangshan region and identified that the gaseous anomalies are consistent with the trace of the Tangshan faults. Though soil gas investigations in the capital area have been made and some gratifying achievements have been obtained, the difference in fault activities in the capital area has seldom been systematically investigated by means of soil gas survey.…”

Soil mercury spatial variations in the fault zone and corresponding influence factors

“…Mercury is widely used in earthquake monitoring and prediction and active fault detection in China (Tang et al 2004;Liu 2006). For example, anomalous mercury contents in wells or springs have been linked to earthquakes (Zhang et al 2005), and gaseous mercury concentrations in soils have been used to detect buried active faults (Wang et al 1991(Wang et al , 2006Li et al 2013). Because mercury is an effective tool for tracing deep fluid activity (Stoffers et al 1999), it plays an important role in revealing the relation between fluid activity in fault zones and the mechanisms by which strong earthquakes occur.…”