Both you and I bear responsibility for this accident.
Literal
I-[also-も] you-[also-も] this accident [for-には] responsibility [subject-が] exist.
The double-も pattern (Aも Bも) means 'both A and B' when the predicate is positive. 責任がある ('to have responsibility') is the standard phrase for bearing responsibility. には marks the scope ('for this accident'). A responsibility-sharing statement.