напишите вот так:
location ~*
^.+\.(jpg|jpeg|gif|png|svg|js|css|mp3|ogg|mpe?g|avi|zip|gz|bz2?|rar)$ {
root /home/username/data/www/site.ru;
access_log /home/httpd-logs/site.ru.access.log;
try_files $request_uri @fallback;
}
Posted at Nginx Forum: http://forum.nginx.org/read.php?21,146504,146534#msg-146534