When faults diverge – High resolution imaging of an intra-fault zone in an urban environment. A case study from the city of Tiberias, Israel

Abstract

The presence of active faults or potentially active faults in urban settings is of great concern to city planners and developers. The high value of property within cities means that it is not always possible to avoid construction in such areas. Thus, building codes exist in order to regulate where and how to build in the vicinity of such faults. The Israeli National Building Code defines a zone of active faulting as a 200-m wide area on each side of an active or potentially active fault trace. In this area, there is a high potential for repeated activity of undetected branches or secondary faults and construction should be avoided or built with extreme safety measures in place. The current study examines an area located between two fault strands – an active and a potentially active one - in the city of Tiberias, northern Israel. The area lies outside the active fault zones defined for each strand (i.e., at a distance of more than 200 m from each fault). Eight high-resolution ground penetrating radar (GPR) profiles were collected along the streets that crisscross this area. Results show a dense series of potential fault strands that reach the base of the artificial fill that was laid down for the construction of the roads, indicating potential seismic hazard in this seemingly “safe” zone, thus raising a “red flag” for construction plans in the area. A geological study should be conducted to validate the geophysical results. This study shows the importance in conducting a geophysical site survey in tectonically active settings, even in areas that lie outside well defined zones of active faulting.