5:15 PM - 6:30 PM
[SIT12-P01] Strain rate dependency of b-values of oceanic intraplate earthquakes
Keywords:Oceanic intraplate earthquakes, b-value, Oceanic lithosphere
In this presentation, we report candidate of explanation of this gap and remarkable results. We revealed that b-values of OCEQs show clear age dependency. OCEQ b-values in young oceanic lithosphere (<15Ma) are around 1.0, those in middle age (15-30Ma) are around 1.4, and those in old age (>30Ma) are around 1.7, which is significantly higher than b-values in the world. If b-value is greater than 1.5, contribution of small earthquakes on total seismic moment release becomes significant. Thus, we suggest that missing seismic moment release in old age oceanic lithosphere is released by unobservable (Mw<5.0) small magnitude earthquakes.
We also found that b-value of intraplate earthquakes in the Ninety East-Sumatra orogen, where oceanic lithosphere has higher strain rate than it of normal oceanic lithosphere, is 0.93, which is significantly smaller than OCEQ b-value (1.7) at the same age. Thus, we conclude that OCEQ b-value age dependency relates to the age dependent slow strain rate of the oceanic lithosphere and is not caused by age dependent thermal structure.