Theory and application of setback distance from active faults

Determining setbacks from active faults is the "last 1 km" from active fault surveys to their application to seismic disaster mitigation. It is also a technique for blocking the risk sources of earthquake-induced chains of geologic hazards. Field investigations and experimental studies have demonstrated that buildings and structures can be free from catastrophic destruction caused by coseismic ruptures and offset of active faults provided they are kept at a certain finite distance from the active fault traces. Therefore, determining setbacks from active faults serves as an ultimate goal of the surveys and precise localization of active faults. Based on the definitions and terminologies related to setbacks from active faults, this study systematically analyzes the width of earthquake rupture localization of various active faults, the hanging-wall effects of surface ruptures/disasters induced by dip-slip faults, and the shearing and tearing of buildings and structures caused by the coseismic ruptures and offset of active faults, which jointly shape the spatial distribution of destruction zones. These characteristics constitute the theory of setbacks from active faults. Accordingly, this study highlights the application scopes of standards for setbacks from active faults, the bases and ranges for delineating the regulatory zones of active faults, the positioning accuracy of setbacks from active faults required for construction sites, and the basic setback distance (D₀) for general buildings and structures within the regulatory zones around active faults. This value can be used as the minimum distance for setbacks from the foot walls of nearly vertical strike-slip faults and dipslip faults. It is recommended that the setback distance from the hanging walls of normal faults with dip angles of about 60° and reverse faults with dip angles of about 30° should be approximately twice and 3 to 4 times D₀, respectively. For particular buildings and structures, different from general ones, their safety directly influences social stability and national prosperity. Therefore, this study presents classified setback distances specific to these buildings and structures to ensure that they will not induce serious secondary disasters during earthquakes. Finally, this study briefly introduces domestic and international laws/regulations concerning setbacks from active faults, along with illustrative examples. As a scientific and effective technique for blocking earthquake-induced geologic hazards, determining setbacks for active faults can effectively determine setback means and distance for the anti-rupture of buildings and structures. Furthermore, this technology provides innovative technical support for ensuring the seismic safety of the sustainable economic and social development of China and the infrastructure construction of the Belt and Road Initiative proposed by the country.