New GPS station network and elastic half-space modeling of Nepalese Himalayan tectonics and earthquake hazard
BETH PRATT-SITAULA1, BISHAL NATH UPRETI2, 1Central Washington University, USA 2Tribhuvan University, Nepal
Considerable controversy still exists over if and how climate and orogenic evolution may be coupled. A prime example of this debate centers on the Himalayan front where profound gradients in both precipitation and topography occur in a similar location – roughly coincident with the Main Central Thrust Zone (MCT) (Fig. 1). Some researchers (e. g., Hodges 2006; Wobus et al. 2005) suggest that the high precipitation rates drive high erosion rates and thus out-of-sequence thrusting and channel flow in this region. Others think the evidence points to a steeper sub-surface ramp causing the topographic rise and thus capturing higher precipi tation rates (e.g., Bollinger et al. 2006; Robinson et al. 2006). In one scenario climate is a driver of orogenic development, in the other it is a passive responder. Some field work suggests that out-of-sequence thrusting is occurring (Mukul et al. 2007). However, a more detailed understanding of modern ground motion will help to determine if out-of-sequence thrusting is indeed occurring. To this end, a new permanent GPS network is being established in the Nepalese Himalaya, which provides greater northeast-southwest transect density of stations than the newly established Caltech network (Bollinger et al. 2006) and more continuous coverage than the campaign GPS (Bilham et al. 1997) of the 1990’s. Six stations were established in June 2008 and an additional 12-15 are planned as funding is secured.
Work is also underway to use an elastic half-space model to predict expected surface deformation under different active fault scenarios. Model results will be compared to the GPS results.
The project is a joint venture between Central Washington University, USA and Tribhuvan University, Nepal. The influx of permanent GPS stations into Nepal will help
better determine if Indian and Nepalese ground motion truly differs (Jade et al. 2007). In addition to helping determine likely tectonic models for the Nepalese Himalaya and give insights into climate-vs-tectonic drivers, this project should help us better understand earthquake hazards in Nepal. For instance, whether only one near-surface fault (Main Frontal Thrust–MFT) is active versus several active faults has considerable impact on earthquake-associated hazards.
Bilham, R., Larson, K.M., Freymueller, J.T., Jouanne, F., Le Fort, P., Leturmy, P., Mugnier, J.L., Gamond, J.F., Glot, J.P., Martinod, J., Chaudury, N.L., Chitrakar, G.R., Gautam, U.P., Koirala, B.P., Pandey, M.R., Ranabhat, R., Sapkota, S.N., Shrestha, P.L., Thakuri, M.C., Timilsina, U.R., Tiwari, D.R., Vidal, G., Vigny, C., Galy, A., de Voogd, B. 1997. GPS measurements of present-day convergence across the Nepal Himalaya. Nature, 386, 61-64. Bollinger, L., Henry, P., Avouac, J.P. 2006. Mountain building in the Nepal Himalaya: Thermal and kinematic model. Earth and Planetary Science Letters, 244, 58-71.
Hodges, K. 2006. Climate and the evolution of mountains. Scientific American, 295, 72-79. Jade, S., Mukul, M., Bhattacharyya, A.K., Vijayan, M.S.M., Jaganathan, S., Kumar, A., Tiwari, R.P., Kumar, A., Kalita, S., Sahu, S.C., Krishna, A.P., Gupta, S.S., Murthy, M.V.R.L., and Gaur, V.K., 2007, Estimates of interseismic deformation in Northeast India from GPS measurements. Earth and Planetary Science Letters, 263, 221-234. Mukul, M., Jaiswal, M., and Singhvi, A.K., 2007, Timing of recent outof- sequence active deformation in the frontal Himalayan wedge; insights from the Darjiling sub-Himalaya, India. Geolog 999-1002. Robinson, D.M., DeCelles, P.G., and Copeland, P., 2006, Tectonic evolution of the Himalayan thrust belt in western Nepal: Implications for channel flow models. Geological Society of America Bulletin, 118, 865-885. Wobus, C., Heimsath, A., Whipple, K., and Hodges, K. 2005. Active out-of-sequence thrust faulting in the central Nepalese Himalaya. Nature, 434, 1008-1011.