Accidentally used dd on my system drive
Your main disk uses a Core Storage partition scheme:

disk0 is your main system disk.
disk1 is a &quot;virtual&quot; disk residing in disk0s2 containing the Macintosh HD volume visible on your desktop.

The first two sectors of a Logical Volume contain zeros only.
Examples:

disk2 is the Core Storage Volume pooling disk0s2 (SSD) and disk1s2 (HDD) of a 3.1 TB Fusion Drive


disk2 is the Core Storage Volume residing in disk0 - the 64 GB disk image of a Parallels VM (Yosemite)



With your command sudo dd if=/dev/zero of=/dev/rdisk1 bs=1024 count=1 you had luck and you just have overwritten 1024 zeros with 1024 zeros.
As a result you haven't lost any data and may continue working with your Mac without the need to restore any backup or to reinstall your system.