Statistics about the occurrence frequency of earthquakes (1973-2015) at shallow, intermediate and great depths along the Izu-Bonin-Mariana (IBM) Arc is presented and a percent perturbation relative to P-wave mean value (LLNL-G3Dv3) is adopted to show the deep structure. The correlation coefficient between the subduction rate and the frequency of shallow seismic events along the IBM is 0.605, proving that the subduction rate is an important factor for shallow seismic events. The relationship between relief amplitudes of the seafloor and earthquake occurrences implies that some seamount chains riding on the Pacific seafloor may have an effect on intermediate-depth seismic events along the IBM. A probable hypothesis is proposed that the seamounts or surrounding seafloor with high degree of fracture may bring numerous hydrous minerals into the deep and may result in a different thermal structure compared to the seafloor where no seamounts are subducted. Fluids from the seamounts or surrounding seafloor are released to trigger earthquakes at intermediate-depth. Deep events in the northern and southern Mariana arc are likely affected by a horizontal propagating tear parallel to the trench.