There is no one way to respond to a traumatic event. But retreating into his shell would not be unusual. The Body Kerps the Score is written by the head of the Harvard Trauma Centre - a psychiatrist. Not woo at all, with lots and lots of data to back up what he says.
What you should be looking at, if you want to direct your search, is the type of trauma he's experienced. Look for support groups on FB and forums dedicated to it to read some of what other people have gone through. Look for websites about that specific trauma. As an example, experiencing a tsunami is a traumatic event. So is being carjacked. So is being raped by a stranger. So is being raped by a long term partner. They all have different aspects which impact the individual and how they respond.
Send him sms to say you love him. You're there. You're thinking of him. And don't necessarily write it in a way that needs a response. Tell him you're not going anywhere and are there whenever he wants to talk, and you're there if he doesn't want to talk.
It sounds like something he should be getting support for. I hope he is.
And remember that he's HIM. You can read every account in the world, which will point you in the right direction, but how he is responding to it will be in his way. So as you know him, you can be sensitive to how he is. For example some people would appreciate being given a helpline phone number. Some wouldn't. Some would be touched to know you'd looked for it, some would be annoyed.
And remember that his responses are about him. If he's angry at you, or shutting you out, it's not nice, but it's not you he's actually angry/silent at.
Sorry that he's gone through this and that you are too.