New Mexico Geological Society Annual Spring Meeting — Abstracts

Determining fault-scarp chronologies is important in the assessment of earthquake hazards and to paleoseismology. In arid environments the low abundance of organic carbon often prevents ¹⁴C dating of displacements; therefore, in these regions fault-scarp diffusion modeling has been applied to date scarps. A drawback to this technique, however, is that the geomorphic diffusivity is often unknown and must be estimated. Because the diffusivity of unconsolidated material can vary by three orders of magnitude a large amount of uncertainty is introduced into the calculated age of a scarp. Better estimates of a scarp age can be obtained by constraining the value of the diffusivity using a cosmogenic nuclide. Samples, collected along two vertical transects near the fault plane of the Socorro Canyon Fault (central New Mexico), were analyzed for ³⁶Cl. The analyses provided vertical ³⁶CI profiles that were used to calibrate a model that couples the accumulation of ³⁶CI to fault-scarp morphology. The calibration of the model allowed the diffusivity to be constrained and the timing of ruptures to be assessed. Preliminary results suggest the surface was displaced around 120 ka and 44 ka. The geomorphic diffusivity is approximately 0.0004 m² / y.