Soil gas radon measurements for investigating the actual status of seismic quiescence along the bounding fault of the Ghab pull-apart basin in western Syria

Abstract

The aim of the present work was to investigate possible spatial fault-related radon changes, which could reveal some important features related to the active nature of local tectonics along the bounding fault of the Ghab basin. Despite its active historical record, the Ghab fault is presently characterized by apparent lack of earthquake activity with a temporal period of seismic quiescence. Seven sites were selected to perform soil radon sampling along the fault using an AlphaGUARD radon monitor. The average background of normal radon emission from local soil and rocks was established apart from the tectonic influence of the fault zone. A statistical range of anomalous radon variation was defined by the limits of the mean value plus/minus two standard deviations (X±2SD). The initial results revealed high radon increases in the sampled stations along the fault zone, with peak values about 4-5 times above the background level. Although such relatively anomalous concentrations may confirm the usefulness of soil gas radon as a possible indicator for tracing the basin-bounding fault, they do not necessarily prove a definite relation with actual active tectonics in the area. However, these increases may possibly indicate evidences of enhanced radon response to a higher permeability medium associated with the deformed structure of the rupture zone.