It's -10% for both ToHit and Def. And both do show in Mids' in the effects tab.
I was adviced once on forums by several people just to slot Earthquake with 3xrchg on my Earth/Rad, at the end of the day, while foes are getting knocked down, they aren't going to hit you much and you get enough -def from your radiation powers so I decided to follow the advice and so far it works fine.
Like Nightmarer said its not worth slotting for tohit debuffs, just slot 3x recharge and throw 2 dam procs in it 
Defiant's GoEH/MILITIS METUS
I certainly wouldn't bother slotting it for -DEF.
Quicksand's -DEF is enough bigger that even 3 slotting Earthquake for -DEF won't get you up to Quicksand's (unenhancable) level, and Quicksand recharges faster than its duration even unenhanced so you can keep it up all the time rather than invariably not having it up when you want it.
As for ToHit Debuffs:
Hmmm, well Radiation Infection is lots better, but yes on a fast moving team, the combination of your anchors getting killed, the slow animation time, and your control powers being slightly higher priority in a lot of situations, I guess it might be helpful to have another string to your bow depending on your playstyle.
However, personally if I had some extra slots above the 3xRecharge, I'd look at putting in some of the Proc IOs from the either the ToHit Debuff or Def Debuff sets. The Chance of Resistance Debuff one from 'Achilles Heel', would be my top candidate, despite my being pretty sure it falls into the 'not exactly cheap' price range 
Or you could do three from 'Touch of Lady Grey' or 'Dark Watchers Despair' and get a Recovery bonus, in addition to the enhancement to either Defense Debuff or ToHit Debuff. I suspect that's probably getting into the 'really not cheap at all' ranges especially if you include the Procs from those sets (Chance of Negative Energy Damage for Lady Grey, or Chance of Recharge Slow for Dark Watcher).
..thinking about that, how about 6 slotting, and going:
Dark Watcher: ToHit Debuff/Recharge
Dark Watcher: ToHit Debuff/Recharge/End
Dark Watcher: Chance of Recharge Slow
Lady Grey: Def Debuff/Recharge
Lady Grey: Def Debuff/Recharge/End
Lady Grey: Chance of Negative Energy Damage
Two sets of Recovery bonuses, and I think the Recharge would be somewhere around about the same as with three standard Recharge SOs, but I haven't actually calculated it...
...nor have I looked at the prices
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I was adviced once on forums by several people just to slot Earthquake with 3xrchg on my Earth/Rad, at the end of the day, while foes are getting knocked down, they aren't going to hit you much and you get enough -def from your radiation powers so I decided to follow the advice and so far it works fine.
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I think for Earth/Rad that would be true - it can vary a little with context. On my Earth/Storm I spam Stone Cages like crazy to leverage damage from Tornado and Lightning Storm. That means Earthquake essentially acts as a debuff and is much more worth slotting for -ToHit (still don't bother with -Def, though). In my case it gets +Recharge, -ToHit and an Achilles Heel proc for a little extra -Res. Nice!
By my 50s shall ye know me:
Tundra, DVM, The Late, Neutrino Ghost, Sir Clanksalot, End Of Days, Prof. Migraine
Howler Monkey
Cheers for the replies...think i'll stick with 3 recharge, then when slots become spare and inf becomes plentyful, i'll stick some proc's in there.
Btw Chin, I see you finally rolled an earth/rad to pair with your GF's fire troller, you having fun with it so far? Mine's at lvl 41 and he's going to be my main toon on DXP
Yeah, been great fun so far...the damage is a bit meh', but the vet powers make a real difference (never remember the Nemi staff being that powerful) and hoping to get him to atleast the pet stage as hes just about to hit 21....then I need to work my g/fs troller as shes not gunna be about, thats the time that i'll be probably get jealous
I've just got my Earth/Rad to lvl18 and picked Earthquake, now when I went to slot it I noticed that it also takes ToHit Debuffs and Def Debuffs. What I want to know are these actually worth slotting for after i've slotted for recharge, on Mids it says that the Def Debuff is something like 10%, but doesn't actually give figures for the Tohit Debuff.