Earth Shock is a core shaman ability learned at level six. It is an instant cast spell that causes an amount of nature damage and reduces the target's physical damage dealt for 30 seconds.
Prior to patch 2.0.3, Earth Shock generated threat equal to twice its damage. The bonus threat was removed from Earth Shock, while [Frost Shock] gained bonus threat.
Patch changes
/Patch 4.0.1 (12-Oct-2010): Attack speed reduction of the target increased to 20 %.
Patch 3.2.0 (04-Aug-2009): Redesigned. This spell no longer interrupts spell casting, but rather reduces melee attack speed by 10% for 8 seconds (exclusive with similar effects such as Thunder Clap).
Patch 2.3.0 (13-Nov-2007): Interrupting a channeled spell with this spell will now always properly prevent casting spells from the same spell school for 2 sec.
Patch 2.1.0 (22-May-2007): Rank 8 is now properly considered an Interrupt effect for talents and abilities that affect interrupts.
Patch 2.0.3 (09-Jan-2007): no longer causes increased threat.
Patch 1.4.0 (2005-05-05): The visual for ranks two through seven has been changed to be consistent with rank one.