AWS has multiple teirs of storage options in s3, some replicate and some dont. by default those that do replicate do so in multiple availability zones, but not across regions. unless you turn on cross-region replication (CRR) which is an additional charge.

So, for example without CRR if your bucket is in us-east-1 and 1 availability zone goes down you can still access the data, but if all of us-east-1 is down, you cannot.