The sell-off in bank stocks Thursday was sparked in part by news Zions Bancorp would write off fraudulent loans made to two borrowers. George Frey / Bloomberg / Getty Images Close Key Takeaways Regional bank stocks rose on Friday, rebounding from a sell-off yesterday as investors assessed the fallout from recent bankruptcies and fraud allegations that have raised concerns about lending standards. The KBW Regional Banking Index gained 1.7% today after slumping 6% on Thursday, when lenders Zions Bancorp (ZIO ...