Crustal shear-wave velocity structure of the Namche Barwa massif, eastern Himalayan Syntaxis, Tibet from ambient noise tomography

Abstract

The eastern termination of the Himalayan orogeny, known as Namche Barwa, serves as a crucial natural laboratory for geodynamic studies of the Tibetan Plateau due to its distinctive geological and geomorphological characteristics. To enhance the understanding of regional tectonics, we deployed a dense array of 374 short-period geophones from June to July 2020 to record continuous waveforms. Using vertical-component data, we computed cross-correlation functions and extracted 13,466 Rayleigh wave phase-velocity dispersion curves for periods ranging from 0.8 to 8 s. We applied the direct surface wave tomography method to invert the three-dimensional shear-wave velocity structure at depths of 0–6 km in the region. Our results reveal that the shallow crustal velocity structure in this region exhibits significant lateral heterogeneity, reflecting the complexity of the geological units. Low-velocity anomalies are primarily observed near faults, including the Indus-Yarlung Suture Zone and the Jiali Fault, while a high-velocity anomaly is detected beneath the Namche Barwa massif. In combination with previous geophysical studies, including magnetotelluric (MT) and seismic imaging results, this high-velocity anomaly is speculated to reflect the intrusion of deep crustal material into the shallow crust. The spatial correlation between the velocity model and seismicity distribution suggests that earthquakes are closely associated with local stress conditions, velocity structure, and the presence of aqueous fluids and geothermal anomalies.