HIGH-RESOLUTION TECHNIQUES FOR EXTRACTING STRUCTURAL DETAIL IN FAULT ZONE EXPOSURES AT RICHMOND ISLAND, CAPE ELIZABETH, MAINE

New digital mapping techniques were used on coastal Maine exposures to extract structural detail within a complex fault zone to better describe and understand the array of fault-related structures. The survey and imaging techniques used included optical total stations for surveying structures, handheld GPS to record and position orientation measurements and 6m and 14m camera poles to collect high resolution low elevation aerial imagery of key structural features in the outcrop surface. Onscreen digitizing in ArcMap 9.3 using georeferenced photo mosaics assembled in Adobe Photoshop was combined with field surveyed structures to give the most detailed and precise fault mapping possible. Three mapping sites were selected on the southwestern shoreline exposure of the Permian-age Richmond Island dextral strike-slip fault zone and included a complex peripheral fault array, a complex main fault structure and a simple single fault structure. Features mapped and measured at each of the sites included strike-slip fault segments, antithetic bookshelf slip surfaces, conjugate shear bands and high-angle kink bands attributed to simple shear, as well as small-scale small dihedral angle conjugate strike-slip faults, and undeformed quartz veins and tension fracture arrays due to pure shear elongation in the host rock. Various techniques were used at each field site in developing a field mapping strategy appropriate for each type of exposure. At the complex peripheral fault array site, an area ~30m² was divided up among three total station teams for surveying major structures. This was supplemented with a 14m camera pole photo mosaic that was used to onscreen digitize key fine scale structures not covered by the total station survey. The complex main fault site contains a ripout lens complex approximately 10m in length, surveyed by a single total station and accompanied by a 6m camera pole mosaic. The single fault site encompasses a simple 15m long dextral strike slip fault, mapped using a hand held eye-level camera mosaic as well as a 6m camera pole mosaic for digitizing onscreen. A combination of a minimum of field surveying with extensive digitizing onscreen from low elevation aerial imagery in the lab proved to be the most precise and time efficient methodology for extracting this type of structural detail for later analysis.