The Tambak Bayan River in Depok District, Sleman Regency, Yogyakarta, features an unusual abrupt bend over Quaternary-aged Merapi volcanic deposits, contrasting with typical river morphology in the region. We analyze microtremor data using the Horizontal-to-Vertical Spectral Ratio (HVSR) method to examine variations in shear wave velocity (Vs) and investigate the subsurface profile at the river bend. These Vs values were used in 2D subsurface depth-profile modeling to illustrate local lithological layering and subsurface heterogeneities. Our model reveals local lithological layering and heterogeneities, with Vs values ranging from 100
to 590 m/s. The observed lithological discontinuities along the bend suggest that the river's bend is influenced by subsurface geological variations. These results offer new perspectives on the geological factors affecting river morphology in this region.
