Bhutan, a kingdom in the Eastern Himalayas, is living in self-imposed isolation: in order to preserve local culture, traditions and the environment, foreigners can enter in groups and in limited number only. Consequently, our geoscientific knowledge is very limited compared to other parts of the orogen. The first geological map was compiled in 1983 by the famous Swiss geologist Augusto Gansser. From a geophysical perspective, Bhutan is almost a blank spot: only very limited information exists on seismicity which shows a lower level of earthquake activity compared to other parts of the Himalayas, and there is knowledge neither of the structure nor of the physical properties of the crust and the lithosphere. Illuminating the deep structure of Bhutan and comparing it with the much better known Central Himalayas of Nepal is highly relevant both for evaluating the earthquake hazard and for improving our geodynamic picture of this classical collisional orogen.
In this project will conduct a temporary seismic experiment in Bhutan. Two densely spaced profiles across the orogen will allow us to produce the first, direct and high quality images of the structure of the lithosphere in the Eastern Himalayas, as well as give an insight into lateral variations along the mountain belt. Together with further stations that we will deploy throughout the country, our network will provide reliable information on seismicity in Bhutan and establish the first seismic velocity model of the crust. Furthermore, we will apply ambient noise tomography to map the physical properties of the lithosphere. The results will be interpreted jointly with gravity data (which we have already acquired) to build physical models of the Eastern Himalayas as well as to draw conclusions on its geodynamics. Especially, seismotectonic studies that we plan to conduct by comparing different segments of the Himalayas may shed light on the origin of the apparent seismic gap in Bhutan.
Augusto Gansser, “Geology Father of the Himalayas” and first geological mapmaker of Bhutan, has passed away earlier this year (2012), at the age of 101. We would like to dedicate this experiment to his memory.
More information about the project is available on: http://www.seismo.ethz.ch/research/groups/alrt/projects/gansser/index