Influence Of Lithospheric Scale Basement Faults On Seismicity In The Himalayan Orogenic System
Authors: Pearce Michelle , Godin Laurent , Gharti Hom Nath 
Published: March 2023

The Himalayan system is the result of a continental collision that occurred approximately 55 million years ago between the Indian and Asian tectonic plates1,2. The collision resulted in the underthrust of the Indian crust beneath Asia, and a deformed crustal wedge3,4. The Indian plate records a complex pre-Himalayan geological history that includes several basement faults that reach depths of 70 kilometres and are oriented at a high angle to the Himalayan front5. These basement faults bound topographic basement highs that are interpreted to limit the rupture of Himalayan earthquakes6. Recent research suggests the basement faults control the distribution and magnitude of seismicity along the Himalaya7. 

The Himalayan system serves as a prototype for novel three-dimensional numerical modelling to understand if and how inherited basement structures influence seismicity in orogenic settings. Models are generated using the Coreform Cubit meshing software and are run on the supercomputer platform hosted at the University of Toronto. The initial model contains three crustal blocks: the Indian crust, a deformed orogenic wedge, and the Asian crust, all cut at a high angle by a lithospheric scale basement fault. The 2015 7.9 MW Gorkha earthquake is simulated, and slip is generated along the Himalayan basal detachment. Seismograms, shear wave potential, and compressional wave potential movies are created to understand if and how the inherited basement faults influence seismicity within orogenic systems. Understanding how these regionally significant basement faults influence seismicity in the densely populated regions of northern India and Nepal is of utmost societal importance. 

References 

1. Najman, Y., et al., (2010). Timing of India‐Asia collision: Geological, biostratigraphic, and palaeomagnetic constraints. Journal of Geophysical Research: Solid Earth, 115. 

2. Hodges, K. V. (2000). Tectonics of the Himalaya and southern Tibet from two perspectives. Geological Society of America Bulletin, 112(3), 324-350. 

3. Godin, L., et al., (2019). Influence of inherited Indian basement faults on the evolution of the Himalayan Orogen, in Crustal Architecture and Evolution of the Himalayan-Karakoram-Tibet Orogen, R. Sharma, I. M. Villa, and S. Kumar, Editors, Geological Society of London Special Publication, 481, 251-276. 

4. Chung, S.-L. et al. (2005). Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism. Earth-Science Reviews 68, 173–196. 

5. Godin, L., & Harris, L. B. (2014). Tracking basement cross-strike discontinuities in the Indian crust beneath the Himalayan orogen using gravity data – relationship to upper crustal faults. Geophysical Journal International, 198, 198-215. 

6. Gahalaut, V. K., & Kundu, B. (2012). Possible influence of subducting ridges on the Himalayan arc and on the ruptures of great and major Himalayan earthquakes. Gondwana Research, 21(4), 1080-1088. 

7. Gahalaut, V, K., & Arora, B. R. (2012). Segmentation of seismicity along the Himalayan Arc due to structural heterogeneities in the under-thrusting Indian plate and overriding Himalayan wedge. Episodes Journal of International Geoscience, 35(4), 493-500.