Seasonal modulation of seismicity in the Himalaya of Nepal

L Bollinger (1) , F Perrier (2) , Jean-Philippe Avouac (3) , S Sapkota (4) , U Gautam (4) , D.R. Tiwari (4)

1 CEA - Commissariat Energie Atomique
2 IPGP - Institut de Physique du Globe de Paris
3 Division of Geological and Planetary Sciences [Pasadena]
4 National Seismic Centre, Nepal

[1] For the period 1995 –2000, the Nepal seismic network recorded 37 ± 8% fewer earthquakes in the summer than in the winter; for local magnitudes ML > 2 to ML > 4 the percentage increases from 31% to 63% respectively. We show the probability of observing this by chance is less than 1%. We find that most surface loading phenomena are either too small, or have the wrong polarity to enhance winter seismicity. We consider enhanced Coulomb failure caused by a pore-pressure increase at seismogenic depths as a possible mechanism. For this to enhance winter seismicity, however, we find that fluid diffusion following surface hydraulic loading would need to be associated with a six-month phase lag, which we consider to be possible, though unlikely. We favor instead the suppression of summer seismicity caused by stress-loading accompanying monsoon rains in the Ganges and northern India, a mechanism that is discussed in a companion article.

Domaines: Planète et Univers [physics]

L Bollinger, F Perrier, Jean-Philippe Avouac, S Sapkota, U Gautam, et al.. Seasonal modulation of seismicity in the Himalaya of Nepal. Geophysical Research Letters, 2007, 34 (8), ⟨10.1029/2006GL029192⟩. ⟨insu-01285780⟩