[1] Compression near collisional plate boundaries causes lithospheric folding which results in the decrease of the pressure beneath the ridge of the fold while the pressure beneath the trough increases. The decompression beneath the lithosphere is likely to bring on basaltic magmatism along and below the ridge. We investigate the subsurface structure beneath Jeju (Cheju) volcanic island and its vicinity, and propose an alternative hypothesis that the basaltic magma beneath the island could be caused by (episodic) lithospheric folding. Unlike the prevailing hypothesis of the intraplate basaltic magmatism that requires extending lithosphere, our hypothesis can explain how the basaltic magma could be generated at the back-arc regions without the extension.

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