The scanning electrochemical microscope (SECM) is used in combination with an electrochemical quartz crystal microbalance (EQCM) to investigate principle modes of tip-induced interactions. The focus is on the influence of acoustic waves and surface modifying processes on the resonant frequency. Considerable importance is attached to high frequency resolution and its enduring accuracy, especially with regard to mechanistic studies of microstructuring processes. A two-dimensional pattern of standing acoustic waves over the entire quartz crystal was monitored for the first time, revealing the anisotropic thickness-shear motion. In the vertical direction, we detected standing pressure waves caused by reflection at the plane apex of the very small tip, which caused frequency changes below 1 Hz. The mass sensitivity distribution of the 10 MHz quartz crystal was mapped two-dimensionally, and an anisotropy due to the orientation of the electrode tabs was found, corroborating published results. The measured mass sensitivity at the center provides a maximum mass resolution of 50 pg, which is sufficient to elucidate mechanistic sequences involved in microstructuring processes.