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Evolution of arc crust and subarc mantle in the Izu‐Bonin‐Mariana (IBM) intraoceanic arc‐trench system is examined by petrological modeling of arc magma generation and differentiation. Characteristic seismic structural features of the IBM arc highlighted in this modeling include the presence of (1) a middle crust with a P wave velocity (Vp) of 6.0–6.5 km/s, (2) a 6.5–6.8 km/s Vp layer at the top of the lower crust, (3) a high‐velocity (Vp = 6.8–7.2 km/s) lower crust, and (4) an uppermost mantle exhibiting rather low velocities (Vp = 7.4–7.7 km/s). The formation of the middle crust, which is considered to have an intermediate composition, is examined by (1) the mantle‐derived basalt model including anatexis of the initial mafic lower crust or mixing of mantle‐melting‐derived basaltic magma with crust‐melting‐derived felsic magma and (2) the mantle‐derived andesite model including differentiation of boninitic magma …