I am a Japanese citizen and lived in an apartment for several years in Portland Oregon while attending school. Because of an emergency with my fathers health and other financial concerns I had to rapidly return to Japan. I could give only 10 days notice instead of the required 30 days. They want me to pay an additional 20 days rent. Does the law protect tenants in this situation?

No, the law protects the owners, You would need to pay for the notice period.