Beats me..........
Thrash or Speed metal is a very wide but usually very confining area of the heavy metal tree. Trademark is the low-end open E string strummed at high speed and usually palm-mutted. A perfect example would be METALLICA's Ride the Lightning album. The vocals are more often than not very rough, although some bands have gone with a more melodic high end singer such as the case with bands like METAL CHURCH or ANTHRAX. Thrash metal like said earlier is very confining and therefore most bands are inclined to include more aspect to their music by adding elements of Speed metal, or even Power metal, of course bands have been known to go the other way and include Death metal traces, as is the case with the occasional TESTAMENT song or even album (if you count DEMONIC). Double-bass drum is a must although they are usually used like a galoping horse rather than a stampede. Its the upper part of the drum kit that gets the most exercise and a good lead guitar player usually takes on the job of coloring the music with little lead licks here and there and ripping solos when the time is right. None of these things i say are set in stone, but they seem to be the formula for countless thrash metal bands. Like any style of music there will always be the bands to steal and stand on the pedistool and overlook everyones elses line of sight! Long live the Thrash Metal band.