Abstract
The Nankai Trough megathrust earthquakes inflicted catastrophic damage on Japanese society and more widely. Most research is aimed at identifying strongly coupled regions that are considered as a major source of future disastrous earthquakes. Here we present a b-value map for the entire Nankai Trough zone. The b value, which represents the rate of occurrence of small earthquakes relative to larger ones, is inversely dependent on differential stresses, and has been used to detect highly stressed areas on fault planes in various tectonic situations. A remarkable finding is that the b value is inversely correlated with the slip-deficit rate (SDR). Moreover, the b value for the areas of high SDR in the eastern part is lower than that in the western part, indicating that differential stress on asperities in the eastern part is higher than that in the western part. This may explain the history of the Nankai Trough earthquakes, in which the eastern part tends to rupture first.
Highlights
The Nankai Trough megathrust earthquakes inflicted catastrophic damage on Japanese society and more widely
A number of studies have been conducted aimed at identifying strongly coupled regions that should be a major source of released seismic energy in future disastrous earthquakes because megathrust earthquakes are driven by interplate coupling[6, 11,12,13,14,15,16,17,18]
Our finding, for large slip-deficit rate (SDR) areas, that the b value in the eastern part is apparently lower than that in the western part (Fig. 3) is somewhat intriguing because it indicates that differential stress on asperities in the eastern part is higher than that in the western part, even if SDRs on the asperities are the same
Summary
The Nankai Trough megathrust earthquakes inflicted catastrophic damage on Japanese society and more widely. The b value for the areas of high SDR in the eastern part is lower than that in the western part, indicating that differential stress on asperities in the eastern part is higher than that in the western part This may explain the history of the Nankai Trough earthquakes, in which the eastern part tends to rupture first. As well as in the Earth’s crust, the b value is known to be inversely dependent on differential stresses[28, 29] In this context, the b value is considered to be a proxy of stress which could help designate asperities or highly stressed patches in the plate interface where future ruptures are likely to occur[21, 22, 30]. We argue that this is the most likely nucleation region for the large event, which would be consistent with the reported rupture history
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