To investigate the structure and attenuation properties of the Lenglongling fault， this study deployed a linear dense seismic array consisting of 118 short-period seismometers along the Daogou segment of the Lenglongling fault， which is the seismogenic fault of the January 8，2022， Menyuan M_S6.9 earthquake. New methane gaseous detonation sources were excited at the northern， middle， and southern sections of the array， respectively. The results show that the dominant frequency band of the methane gaseous detonation signals is 5 to 50 Hz， with an effective propagation distance of up to 7 km. Significant travel-time delays were recorded at stations near the rupture； these delays indicate a low-velocity zone approximately 400 m wide， the location of which is consistent with the surface rupture of the Menyuan M_S6.9 earthquake. The maximum P-wave travel-time delay caused by this fracture zone is about 85 ms， and the delay on the north side is significantly higher than that on the south side， indicating asymmetry in the velocity structure across the fault， which is consistent with the geological background of exposed bedrock on the south side and unconsolidated sediments on the north side. Normalized spectral analysis shows that after the wavefield passes through the fracture zone， the dominant frequency band becomes lower and narrower， and its high-frequency components exhibit more significant attenuation when propagating in the low-velocity fracture zone. This study preliminarily constrains the heterogeneity and medium attenuation properties on both sides of the Lenglongling fault zone， validates the effectiveness of the methane gaseous detonation source in active fault detection， and provides a reference for subsequent high-resolution velocity structure imaging.