Have you ever wondered how large mountain ranges such as the Himalaya grow and where
new faults associated with mountain building form? I’m Mike Duvall from The University
of Alberta along with my co-authors John Waldron from the University of Alberta, Laurent Godin
from Queens University and Yani Najman from Lancaster University, UK, and we have just
published new research in Proceedings of the National Academy of Sciences that we are excited
to share with you.
We are interested in understanding faults of the world’s tallest mountain range, the
Himalaya. Although there are many faults in the mountains, until now, it was thought that
no faults were present in the lowlands to the south. We discovered a series of faults
in front of the Himalaya that have never been seen before. These faults indicate that the
southernmost extent of fault movement in the Himalaya is not at the foot of the Himalayan
mountains as previously thought, but rather 40 km south in the flat Ganga Plain, which
up until now was considered to be undeformed and free of faults.
For more than 100 million years, the Indian subcontinent has been drifting northwards
across an ancient ocean. In the last 50 million years, the ocean closed and India started
to collide with Asia. In the course of that collision, the Himalaya, the largest mountain
range in the world, has been built where two continents collided. India is at present still
sliding northwards into Asia at a rate of nearly two centimetres per year.
Along the front of the mountains are thrust faults, formed where the Indian subcontinent
is pushed underneath Asia. The movement is jerky, which produces earthquakes. Because
this is a densely populated part of the world, these earthquakes can be catastrophic. In
2015, a major earthquake in Kathmandu, Nepal with a magnitude of 7.8, destroyed hundreds
of thousands of homes, killing nearly 9,000 and injuring more than 20,000.
We used two-dimensional seismic reflection data to image what the Ganga Plain looks like
beneath its surface. Seismic reflection images look like slices through the top few kilometres
of the Earth’s crust. These data were originally collected during petroleum exploration, by
recording sound waves bounced off sedimentary layers buried beneath the Ganga plain. These
images provide the first comprehensive picture of the subsurface in this area and highlight
previously unknown faults beneath the Ganga Plain, buried beneath the sediments and not
visible at the surface. We demonstrate that while southeastern Nepal is currently nearly
flat and therefore looks undeformed, the thrusting produced by movement of the tectonic plates
has already reached this area. We also estimate that these faults have moved about 100 meters
over the last 500,000 years. While there have not been any earthquakes
recorded in the area since accurate scientific records began about a century ago, our results
suggest the potential for earthquakes. Most of these faults only slip every thousand years
or so. We have now discovered that a substantial part of this area has an almost horizontal
fault underneath it, which could slip and cause a damaging earthquake. Our research
opens up an important avenue for future seismology research to better understand this newly identified
hazard in the densely populated Ganga Plain. We are also particularly proud to see integration
of work between Industry and Academia result in data used not to only for economic development,
but also for societal good. We thank you for listening, and hope you enjoy
reading our paper!