Abstract - Fault displacements primarily accrue during large magnitude earthquakes, typically producing variable displacement rates through time. To examine the processes that underlie the temporal changes in fault displacement rates we analyse displacements and displacement rates for time periods of 0-5, 0-10, 0-20, 0-300, 0-500, 0-1000 kyr, 0-5000 kyr data on 261 active reverse and normal faults from a worldwide dataset. Displacement rates that derive from short periods of time (e.g. < 20 kyr) depart from million-year average rates by up to three orders of magnitude, typically displaying bimodal fault behaviour with either very high or very low values, while the magnitude of these departures is inversely related to fault size and the duration of the sample period. Over short timescales, the small faults appear to accumulate displacements with rates comparable to the short- and long-term rates of large faults, a feature which suggests more variable growth on small than large faults. Simple earthquake-slip modeling showed that variations in displacement rates require changes in both recurrence interval and slip per event and do not support the Characteristic or the Gutenberg-Richter earthquake models. Over time periods >20 kyr and <300 kyr fault displacement rates become generally constant, with the length of time required for the stability to be achieved being inversely related to the regional basinal strain rates. Stable long term displacements rates and fluctuations in earthquake recurrence intervals and slip arise in part due to fault interactions.
Abstract of talk given to:
International Geological Congress, Oslo, August 2008.