Abstract A joint source inversion analysis integrating teleseismic waveforms, near-field GNSS coseismic displacement, and strong ground motion data was performed to investigate the rupture process of the 2025 ML 6.4 Dapu earthquake in southwest Taiwan. The inversion incorporated two nodal fault planes determined by the real-time moment tensor system, with results indicating that the west-dipping fault plane provided the best fit across all three datasets. Rupture initiated at approximately 10 km depth and propagated southwestward. A single prominent asperity was identified ∼ 10 km from the epicenter in the southwestern region, characterized by a compact slip area with a maximum slip of ∼ 30 cm and an estimated stress drop of 1.0 MPa. The inversion results suggest that the primary seismogenic structure is a west-dipping blind thrust fault in the middle-to-deep crust beneath the detachment. This fault does not reach the surface and exhibits limited interaction with the shallow east-dipping structures. These findings highlight the need to reassess deep structures beneath the detachment in southwest Taiwan.