While most bands of their vintage long ago folded or lost their vitality, Swans have defied nature by creating some of the most riveting and powerful music of their career 30-plus years into it. Leader Michael Gira’s still in thrall to mantric repetition in epic songs that accrue an intensity that’s both punishing and cathartic. Tonight you’ll hear their maniacal, tightly coiled grandiloquence, as represented on Swans’ last two monumental albums, The Seer and To Be Kind. (Showbox at the Market, 1426 First Ave, showboxonline.com, 9 pm, $25 adv/$28 DOS, all ages)