Tire question - sidewall cracks around it nearest to rim

[omodos]

Hello all, only noticed this when washing car and taking a close look. 235/65 R17 Got hairline cracks in sidewall going all the way round, nearest to rim lip,they aren't over all sidewall but about 1inch from rim in the innermost band on outer tirewall . Its only this one rear tire, and they aren't too old, is there anyway to know if it is superficial and or risky to drive X? in the past i have had much worse condition tires and never thought twice , but now I am not along in the car.