SEOmoz, a Seattle-based provider of search engine and social optimization software, has dipped into its $18 million Series B round raised in May to buy Followerwonk, a Twitter analytics firm. The deal, which officially happened in June, but has now come to light following a couple months of tech integration, furthers SEOmoz’s push into social media marketing tool development.

The deal is a small one, and terms were not technically released, but SEOmoz CEO Rand Fishkin says in a blog post that it was between $1 million and $4 million and included cash up front, incentivized payouts and SEOmoz stock.

The "wonk" in Followerwonk’s name is highly appropriate. The software provides deep analytics on Twitter followers by searching bios, the data from which can be sorted, filtered and exported. It also features a "compare users" function that shows follower overlap between users. The meat of Followerwonk’s platform is its Analyze Followers function, which provides details on geographic concentration, influence scores, gender distribution, follower/following counts, age, usage levels, language distribution and most active hours.

The Followerwonk platform has been integrated into SEOmoz’s search marketing optimization software, which, says the company, has about 15,000 paid subscribers.

Fishkin says SEO has played a big role for digital marketers, but social now is where the interest is particularly acute. "Companies are looking into alternative ways to do marketing on the web that’s not merely advertising," he says. "Inbound marketing is a new frontier. The growth in SEO has been big in the last decade, and that will continue, but the trends in SEO and social are so intertwined. The person responsible for SEO is required to manage some social accounts and vice versa. That overlap is where we see the tools going as well."