The Stipsicz conjecture on
the fiber-sum decomposability of Lefschetz fibrations states that nonminimal
Lefschetz fibrations over S2 are irreducible with respect to fiber-sum decompositions
and we can judge that such Lefschetz fibrations are prime and fundamental. In this
paper, we can determine the canonical classes of nonminimal Lefschetz fibrations
admitting spheres of square −1 whose total intersection number with generic fiber is
big. As a consequence, we consider the Kodaira dimension and the geography
problem of such Lefschetz fibrations.