Abstract - Paleoearthquakes at the Earth’s surface often generate variable fault displacement rates. The nature and origin of these variations and the extent to which they result from systematic processes is unresolved. To address this question we use geomorphic and trench data to investigate the source of displacement rate fluctuations over 60 thousand years for normal faults in the Taupo Rift, New Zealand. We find that displacement rates and their stability correlates with fault size, such that smaller faults have lower and more variable displacement rates than larger faults, on time scales less than ca 18 thousand years. Although this variability reflects the complex nature of fault interactions within the fault system, aggregated displacement rates across the entire rift are uniform over a broad range of time intervals from 2 thousand to at least 60 thousand years. These temporal and spatial variations in displacement rates suggest that each fault is a component of a kinematically coherent system in which all faults interact and their earthquake histories are interdependent. Fault interdependencies generate short term complex (<18 ka) fluctuations in the timing and magnitude of earthquakes, but also ultimately result in the stability of displacement rates on longer timescales.
Abstract of talk given to:
Tectonic Studies Group Annual Meeting, Manchester, January 2006.