The Albarregas Fault: Determination Of Its Trace Through Monitoring Radon Gas

The Albarregas fault is an inferred fault running along the Merida terrace, following the course of the Albarregas river. The city of Merida has grown around this fault, occupying the possible area that may be affected by an earthquake along it. With the aim of providing new evidence (other than geological or geomorphological) that contribute to demonstrate the existence of the Albarregas fault, radon soil gas has been monitored near its trace. For sampling, a Pylon AB-5 equipment, with Lucas cells (scintillation cells) was used; 11 localities were sampled along transverse paths (transects) to the river course, and anomalous radon high concentrations were obtained indicating the presence of the fault. These results are important because they provide additional geochemical information on the existence of the Albarregas fault, which was postulated assuming a structural control over the Albarregas river, and assuming the geological contact of two formations underneath the terrace. On the other hand, the results also indicate that radon gas monitoring is a suitable method for determining blind or hidden faults in towns, constituting a useful tool in microzonation works.