Lg Wave Attenuation across the Indo-Eurasian Collision Zone

The collision between the Indian and Eurasian plates has resulted in one of the most tectonically active zones in the world. To characterize the crustal structure and thermal properties of the region, we present a high resolution Lg wave attenuation model along with Lg wave propagation efficiency map for the Indian Shield, the Himalayas, and the Tibetan Plateau and neighbouring areas. Using a dataset comprising more than 1,800 regional earthquakes recorded by 795 broadband seismic stations, we inverted spectral amplitudes using the least squares orthogonal factorization (LSQR) method to map the lateral variation of the Lg wave quality factor (Q_Lg ) and its frequency dependence (η). The resulting tomographic images reveal a sharp contrast in crustal attenuation across the collision zone. The Indian Shield exhibits significant tectonic stability and low attenuation (high Q_Lg ) along with high Lg wave propagation efficiency, consistent with the transmission of seismic energy through a rigid cratonic lithosphere. Conversely, the Tibetan Plateau is dominated by widespread high attenuation (low Q_Lg ) and significantly reduced Lg wave propagation efficiency, with the lowest values observed beneath the Qiangtang and Songpan-Ganzi terranes. The variation in the η parameter highlights the distinction between intrinsic and scattering attenuation, correlating strongly with regional heat flow variations. We observe a clear spatial correlation between low Q_Lg anomalies and the presence of partial melt or aqueous fluids within the Tibetan crust. These results provide new insights into the geophysical understanding of the collision zone and the geometry of the crustal structure.