There are five bands called Ground Zero:
(1) An experimental group from Japan. (See also GROUND-ZERO)
(2) dark hardcore/metalcore band from Serbia
(3) melodic death metal band from Italy.
(4) thrash/death metal band from Japan
(5) hardcore punk band from the US
(6) Progressive metal from Hungary

(1) Ground Zero a Japanese experimental noise/jazz group formed by 大友良英(Otomo Yoshihide) and Altered States with various japanese instrumentalists, sometime noted asGROUND-ZERO.

(2) Ground Zero are from Novi Sad, Serbia - they play a somewhat unique blend of metalcore (modern melodic stuff ala Darkest Hour, and older school mosh like Acme and some holly terror bands) and dark hardcore (portland school - Tragedy, His Hero Is Gone etc.), with some hints of spanish emo/hardcore/metal (bands like Ekkaia, Ictus etc.) and some emo/screamo bands (like Children Of Fall, they play a cover of their "Least Resistance" too).
Myspace: http://www.myspace.com/groundzerohc
Youtube videos: http://www.youtube.com/spaske777

see also Groundzero

(3) Ground Zero as pioneers of this brand new wave of Italian modern heavy metal, GZ's goal is to bring extreme music to a new level, melting together both aggression and melody into a new and fresh style. "The Zero Hour" represents the first step towards the development of their own musical path and an excellent excuse to perform the largest amount of gigs possible in every graveyard or whorehouse near you.

(4) Ground Zero, was an japanese thrash metal (with death metal influences) band. Group was formed in 1983 and have debuted in 1986 with "Etherealize" EP, onliest band's album "Gate of Death" was released in 1987. Now Ground Zero is disbanded. In 2004 the HMSS released live album called "Live Vanguard" with live material recorded in 1986.

(5) Ground zero (US) was a old school hardcore band out of Ann Arbor, Michigan. They were High school mates and started the band around 1982 and played up to 1984., played for fun shows as with SS Decontrol,Suicidal Tendencies, J.F.A., The Necros,Negative Approach, The G.I.'s and most recently Agent Orange and The Misfits. They did reunion show after not playing for 21 years.
check them at: http://www.myspace.com/groundzero1982