'You are responsible' means that 'you could have prevented it if you had acted differently'. In free societies, people are responsible for almost everything that happens in their lives. By taking the proper precautions, you can dramatically reduce the odds of being affected by accidents and violent crimes. With a little bit of intelligence and foresight, you can arrange things to protect yourself from almost all of the hazards of life. For example, you can reduce the chances of your house burning down to almost zero by keeping things clean, eliminating fire hazards, and keeping working smoke detectors and a fire extinguisher. Most house fires result when people fail to do these things, so we can say that the homeowners are responsible for the conditions that let the fire happen.
By contrast, 'You are to blame' is a much stronger and more loaded word that means 'you actively did something morally wrong'. We should only 'blame' people for a fire if they deliberately set the fire. 'Blame' implies 'premeditated crime' and it implies judgment and condemnation. If I walk alone through a bad part of town at night, and I get mugged, then I share responsibility for what happened even though all of the blame belongs to the criminal. I should recognize that my actions were not smart and that I should change my behavior, and everyone else should blame, judge, and condemn the mugger, and only the mugger, for his actions.
I do not know how other people use these words. Some people seem to have the same connotations that I do, but others seem to use them as synonyms. I believe that the latter usage is a mistake. When discussing questions of crime and causality, you should be very careful to respect the distinction between 'failing to act wisely' and 'actively doing something wrong'. Your language should be precise and not sloppy. Theologians do discuss 'sins of omission' versus 'sins of commission' but the state of common language and even legal language on this issue can be dangerously imprecise at times.
For example, consider this news article headlined Women say some rape victims should take blame - survey The headline uses the word 'blame' but the actual article says:
These are two fundamentally different concepts, and they should not be conflated. It is undoubtedly true that women can dramatically alter their chances of being raped by changing their behavior, and it is also (to me at least) unquestionably true that the man and only the man should be blamed for the rape. Women can be partially responsible but they should never be blamed.
Almost three quarters of the women who believed this said if a victim got into bed with the assailant before an attack they should accept some responsibility.
One-third blamed victims who had dressed provocatively or gone back to the attacker's house for a drink.
I would like to see the actual wording of the survey but the BBC, like all legacy news organizations, consistently fails to cite their sources and provide links to the actual research. Therefore, I have no way of knowing the language that was actually used in the questioning and what kind of views that the people surveyed held. I suspect that a survey asking about 'responsibility' would get very different results than a survey asking about 'blame'
The sloppy use of words has poisoned the discussion about crimes, and especially rape. We need to find ways of teaching people to take responsibility for their lives and protect themselves by altering their behavior, while still making it clear that all crimes should be blamed only on the criminal.