I fixed my problems with earthquake being interupted by other casts from my other toons, by using "/stopmacro [channeling]" in all my offensive macro's.

for example.

#showtooltip lightning bolt
/stopmacro [channeling]
/cast [target=focustarget, noharm] Healing Surge
/cast [target=focustarget, harm] lightning bolt

#showtooltip lava burst
/stopmacro [channeling]
/cast [target=focustarget, harm] lava burst

no idea if this goes in conjuction with what stuff ive read so far. but someone might find it useful at some point. (and yes, that was focustarget, please dont laugh :P, only just returned to boxing after 2 years of playing a solo char!!!!!)