Fault investigations generally progress through three Phases:

• • Phase I:  This initial phase includes a literature review of surface faults in the area, a remote sensing study using historical aerial photos and other available imagery, such as LIDAR data, and a field reconnaissance to inspect for physical fault evidence like topographic scarps or building distress.
  • Phase II:  If Phase I identifies fault evidence, Phase II work can be conducted. Phase II investigates if there is displacement due to fault movement associated with the fault evidence using existing data from well logs and geophysical borehole programs. Borings are drilled and geophysically logged to collect subsurface data and interpret the site’s stratigraphy, identifying fault-related displacement. A minimum of two temporary borings installed to a depth of approximately 330 feet below ground surface can confirm the presence of a fault, but typically, a program of four to six temporary borings is required.
  • Phase III:  Phase III involves detailed fault trace mapping using topographic surveys and, if required, geophysically logged boreholes. Surface mapping of the fault trace and profiles across the fault are surveyed at regular intervals, while geophysically logged boreholes, if needed, aim to intersect the fault plane at depth for use in estimation of the fault trace location at the surface. The number and depth of geophysically logged boreholes needed depend on factors such as subsurface layer variability, fault characteristics, and the precision required for fault trace location.