Fault growth is often accomplished by linking a series of en echelon faults through relay ramps. A relay ramp is the area between two overlapping fault segments that tilts and deforms as the faults accrue displacement. The structural evolution of breached normal fault relay ramps remains poorly understood because of the difficulty in defining how slip is partitioned between the most basinward fault (known as the outboard fault, which includes the severed fault tip), the overlapping fault (inboard fault), and any ramp-breaching linking faults. Along the Warner Valley fault in south-central Oregon, two relay ramps displaying different fault linkage geometries are lined with a series of pluvial shorelines that record a Pleistocene paleolake regression. The inner edges of these shorelines act as paleo-horizontal datums that have been deformed by fault activity, and are used to measure relative slip variations across the relay ramp bounding faults. By measuring the elevation changes using a 10m digital elevation model (DEM) of shoreline inner edges, I estimate the amount of fault activity on severed fault tips. In order to attribute shoreline deformation to fault activity I identify shoreline elevation anomalies, where deformation exceeds a ± 0.3% window from normalized elevation values; this encompasses my conservative estimates of natural variability in the shoreline geomorphology and the error associated with the data collection. For each ramp-breaching fault style activity is concentrated near the fault linkage site. Even after a ramp is fully breached the severed fault tip temporarily retains some connectivity to the main fault segment. Severed fault tips along a mid-ramp breach tend to be more active than the severed fault tip at a footwall breach. Persistent fault activity along the entire severed fault tip is dependent on the position of the linkage. These results indicate that on the time scale of 104 years after linkage, severed fault tips persist as active structures and accommodate meaningful amounts of strain.
