Does seeking forgiveness expiate major sins?

Seeking forgiveness (istighfar) has great virtue and abundant good. However, istighfar coupled with repentance (tawbah)—with its conditions (remorse, ceasing the sin, and resolving not to return to it)—is what expiates major sins. As for merely seeking forgiveness without repentance from major sins, it does not expiate them, because istighfar is a request for forgiveness, while tawbah means turning away from the sin, abandoning it, and resolving not to return to it.