Monitoring degradation of the Edgecumbe Fault scarp, Rangitaiki Plains, New Zealand

Abstract

Abstract A portion of the Edgecumbe Fault scarp has been fenced and protected to provide a record of the major surface rupture. The site will be monitored to observe the natural degradation of the fault scarp, and it is also the sole remaining record, unmodified by humans or stock, of the surface rupture formed during the 1987 Edgecumbe earthquake. Measurements of the degradation are being made across seven profile lines perpendicular to the rupture at regular intervals. At present the monitoring results have not indicated any change in the free faces. The diffusion model has been shown by a number of workers to be applicable to scarps and is assumed to be the appropriate model for fault-scarp degradation in the Rangitaiki Plains. An assumption of this model is that the time taken for the free face of the scarp to degrade to an angle of repose is short compared with the time span over which diffusion occurs. Data obtained from monitoring of the site over a significant time period, combined with the known recurrence interval of the Edgecumbe Fault, will provide information to test this. In the long term, monitoring may also reveal details of the processes that carry the scarp to an angle of repose.