Maybe you are confused by the words "common stock" in Basel 3 or something -- that's in the stockholders' equity line, book value, and is not defined by the market price of the company's own common shares.

(For example, you can look at PACW's Q1 press release, and see its Tier 1 capital ratio not getting cut by 2/3 by the precipitous drop in share price they endured: https://www.pacwestbancorp.com/news-market-data/news/news-de... )