Can't trust HR

I am currently an employee who would like to know who I can contact anonymously to report a violation between a member of our HR team and a fellow associate. It is in regards to a sexual relationship that has been happening. I am afraid to go to HR since it involves one of their members and don't want them knowing who has reported it. I need an email of someone who can escalate this and start an investigation. Everyone has heard about it but is afraid to report it because it involves HR.