There are several methods which exist to find the risk associated with a region in context of geological faults and the exact methods are best left to the experts to decide depending on individual case but a broad overview of the different perspectives is as follows.
History: the seismic history of a region is certainly helpful to extrapolate the future occurrence of similar events. However this historical evidence should be based on verifiable sources and appropriate technical data, and not simply on hearsay.
Surface Scanning: this can be done by taking aerial photographs of various features as well as mapping of various structures and zones, studying the fluctuations in ground water level and so on. This would indicate the presence and severity of the geological fault in the region.
Sub Surface Scanning: there is lot of information under the surface as well which could be useful in predicting the fault conditions in the area. Pits and trenches can be made which can be used to measure characteristics such as resistance, magnetism and other physical and chemical properties of the materials that comprise the subsurface level.
There are several other tests which can be used depending on the situation and these could include test such as radiometric analysis and so forth. It is beyond the scope of this article to discuss these techniques in detail.