Nature of crust beneath Sri Lanka using teleseismic receiver function

Sri Lanka occupied a unique position in the Eastern Gondwana assembly, surrounded by its Gondwana neighbours: Madagascar, India, Antarctica and Africa. It comprises four distinct lithologic units: the Highland Complex, the Wanni Complex, the Vijayan Complex and the Kadugannawa complex. Crustal properties (crustal thickness and velocities) in Sri Lanka have been estimated by inversion modeling of receiver functions computed using earthquake data from three stations that operated between 2011 and 2018. Results reveal ~38 km crustal thickness and high average shear wave velocity (Vs ~ 3.7–3.8 km/s) beneath Sri Lanka, low average Vp/Vs ratio (~1.72) in the Highland Complex, and high Vp/Vs ratio (1.79) in the Wanni Complex. This suggests that the crust beneath Sri Lanka is felsic to intermediate in nature and the probable rocks are of granite to granodioritic in composition. The probable rocks in Wanni Complex are felsic to mafic granulite in nature. The crustal thickness and average Vp/Vs ratio in the Highland Complex shows similarity with its Gondwana neighbours, denoting its unique position in Gondwana. The average crustal shear wave velocity in Sri Lanka is also found to be high (~3.7 km/s), which is also comparable with its Gondwana neighbours.