The crustal structure of the Himalaya: A synthesis

Abstract This chapter examines the along-arc variation in the crustal structure of the Himalayan Mountain Range. Using results from published seismological studies, plus large teleseismic body-wave and surface-wave datasets which we analyse, we illustrate the along-arc variation by comparing the crustal properties beneath four representative areas of the Himalayan Mountain Range: the Western Syntaxis, the Garhwal–Kumaon, the Eastern Nepal–Sikkim, and the Bhutan–Northeastern India regions. The Western Syntaxis and the Bhutan–Northeastern India regions have a complicated structure extending far out in front of the main Range, whereas the Central Himalaya appear to have a much simpler structure. The deformation is more distributed beneath the western and eastern ends of the Range, but in general, the crust gradually thickens from c. 40 km on the southern side of the Foreland Basin to c. 80 km beneath the Tethys Himalaya. While the gross crustal structure of much of the Himalaya is becoming better known, our understanding of the internal structure of the Himalaya is still sketchy. The detailed geometry of the Main Himalayan Thrust and the role of the secondary structures on the underthrusting Indian Plate are yet to be characterized satisfactorily.