From the AWS documentation.
When you create an EBS volume in an Availability Zone, it is
automatically replicated within that zone to prevent data loss due to
failure of any single hardware component. After you create a volume,
you can attach it to any EC2 instance in the same Availability Zone.
Amazon EBS provides the ability to create snapshots (backups) of any
EBS volume and write a copy of the data in the volume to Amazon S3,
where it is stored redundantly in multiple Availability Zones. The
volume does not need be attached to a running instance in order to
take a snapshot. As you continue to write data to a volume, you can
periodically create a snapshot of the volume to use as a baseline for
new volumes. These snapshots can be used to create multiple new EBS
volumes or move volumes across Availability Zones.
Here’s some background for you about regions and availability zones, which you appear confused in your question.
Amazon EC2 is hosted in multiple locations world-wide. These locations
are composed of regions and Availability Zones. Each region is a
separate geographic area. Each region has multiple, isolated locations
known as Availability Zones. Amazon EC2 provides you the ability to
place resources, such as instances, and data in multiple locations.
Resources aren’t replicated across regions unless you do so