select id, post_title, post_date, post_modified
from wp_posts
where post_type='post' and post_status='publish' and post_date<>post_modified
order by post_modified desc
limit 0,10

$query = new WP_Query(array('orderby' => 'post_modified', 'order' => 'DESC', 'post_type'=>'post','post_status' => 'publish') );