[S-SS08] 地震活動とその物理

[SSS08-08] Modulation of Nepalese Seismicity by Transient Loading : Seismicity Rate and b-value

*Martin Colledge^1,2、Kristel Chanard³、Alexandre Schubnel¹、Laurent Bollinger² (1.ENS PSL - Ecole Normale Superieure, Laboratoire de Geologie, Paris, France、2.CEA - Commisariat a l'Energie Atomique - DAM DIF, France、3.IPGP - Institut de Physique du Globe de Paris, France)

キーワード：Nepalese Seismicity, Seasonal Variations, b-value, Hydrological Loading , Periodicity

Nepal's seismicity has been shown to display a seasonal component in its temporal distribution, but the mechanism responsible for this seasonality remains unresolved, with surface loading and seasonal fluid diffusion being invoked. We investigate the hypothesis that monsoonal loading and unloading of the main seismogenic structure of the Nepalese Himalayas control the seasonal nature of its associated interseismic seismicity between 1994 and 2014. Using large-scale mass distribution data, we resolve the stress tensor variations generated at depth by transient surface loads. Hydrological surface loading of the Nepalese Himalayas correlates with certain features of the seismicity rate over the 15 years considered. More specifically, the maximum Coulomb stress rate on the Main Himalayan Thrust (MHT) correlates with a 20% increase in the seismicity rate. The Gutenberg-Richter b-value is also investigated, with statistically significant annual variations between 0.9 and 1.05 being detected, although the relation to stressing cannot be constrained.