Anomalous paleoflow orientations: A potential methodology for determining recurrence rates and magnitudes in paleoseismic studies

In southwestern New York State paleoflow data collected from Upper Devonian sandstones in areas of known north-striking, syndepositionally active faults of the Clarendon-Linden fault system contain anomalous north-south-trending paleoflow orientations. If the faults were active during deposition, then topographic relief generated as a result of faulting may have influenced the paleoflow direction in the immediate area of the active fault. On the basis of a simplistic model, we assume that the normally west-directed flows were redirected north-south along a north-striking fault scarp. Using anomalous-trending paleoflows, the height of the scarp (fault displacement) can be estimated from the uncompacted thickness of stratigraphic section that contains the sequence of redirected flows. We can estimate the maximum magnitude of the seismic event from the fault scarp height (assuming the fault scarp was developed from a single seismic event). Recurrrence rates can be estimated from the uncompacted thickness of stratigraphic section with west-directed flows between successive sequences of north-south flows. Using uncompacted stratigraphic thickness as an estimate of the surface offset, magnitudes of potential earthquakes on the Clarendon-Linden fault system are estimated to be between 6.0 and 6.9. Using a range of accumulation rates of 10 to 30 cm/k.y., the average recurrence rate for an earthquake of magnitude 6 or greater during the Late Devonian was estimated to be between 8100 and 24 300 yr. This rate is comparable to the average recurrence rate of 4800 to 14 400 yr obtained from seismites in the stratigraphic section.