What makes Joe Brody think it wasn't natural?

He thinks that it was a creature because the graph wasn't moving like an earthquake, it was moving like a creature or something living. It wasn't an earthquake that caused the plant to fall it was something living.

Ce n'était ni un tremblement de terre ni un typhon! 

It wasn't an earthquake, it wasn't a typhoon! 

he knew it wasent naturel because A FRIGGN GODZILLA CAM OUT OF THE RUBBLE!!! XD sorry but i agrea with @Godzilla 2014 himself that he saw something on the graph or a nucler power plant just dosent fall over

In the interviews that were done around the time the 20 minute footage tour was being done, they reveal that he knew it wasn't an earthquake because the seismic readings didn't match what an earthquake or natural disaster would look like. 

Something about how the tremors came in at consistent, repeated intervals, rather than more random and jagged. 

He doesn't necessarily know it was an animal or a creature. He just knows that something is up and he isn't being given the truth. 

Thats a good question!  They are being delightfully (a.k.a. infuriatingly) vague about the details of this movie and this sequence, despite the Janjira Incident being the thing we know most about in the film so far.  I think the instruments in the facility pick up a signature that doesnt match an earthquake, but is consistant with an living organism.  Maybe Joe is the only one who sees it!  Maybe he sees someting else... a claw or tail perhaps?  We don't really know if it is Godzilla or a Muto that causes the destruction of the plant, but it seems that something causes a subteranian malfunction and/or a structural crisis.  Unless Godzilla is a burrower, my money is on a smaller Muto causing the incident, as it could go about its business in a more covert manner.  If it were Godzilla, chances are he would have been spotted.  Remember, the 8 legged "Hokmuto" has been described as much smaller than Godzilla.  Maybe Joe saw a portion of the creature's body, but chances are he is tipped off by a bizzare signature on an instrument of some sort.  Being that the plant is in Japan, chances are they would have earthquake sensing equipment on hand, as earthquakes are common in Japan and a bad one could compromise the facility.

I personally think it's fun to speculate that the MUTO are using their EMP or some other type of pulse to create the sinkholes, and unburrow themselves....obviously preferring to unburrow close to nuclear or radioactive locations. 

And the pulses are what the seismographs are picking up, not the animal or tunneling movement. 

I dunno, I personally think them saying 'the seismic activity matches animal activity' is just kinda silly, because there are almost no animals that create seismic activity.....so nobody would have any real idea of 'animalistic' seismic readings would look like. I'm sure they could find some workaround for that problem to justify the dialogue, but it would still be pretty cheesy. 

I prefer the readings to be suspicious, but mysterious in origin, rather than clarified as animalistic early in the film. Which is exactly the route they seem to be taking to me :-)

Godzilla 2014 Himself, nice name :D

Thanks!!! :D Also Godzilla Himself nice name! XD

You two up there ^^ are related haha jk but hey nice answer thats what i thought too

Doesnt any body think of JAWS when they hear the charachters last name BRODY?

Chief Brody.

I hope audiences and critics wont mind that.

@Kaijujira:

I wouldn't be too woried about that!  There isn't a rule that you can't give your characters a name like Brody because another movie happened to use that name.

But you are totally right!  The name definitely brings Jaws to mind!  Its a name that harkens back to an older time in Hollywood, and conjurs up warm feelings of classic adventure films like Jaws and Close Encounters.  Its little wonder that Gareth Edwards has cited those films as inspirations for Godzilla!  He has mentioned Jaws as being one of his favorite films several times, so there is a fair chance that the name Brody is an homage to the original summer blockbuster! :) 

@awesomejaijufan, how do u know A GODZILLA came out of the rubble? cuz I'm just wondering ?

and I think he saw a HokMuto cuz the seismic graph is the same as the pic where it showed Staittharen and the graph is the expact same!

There are a number of things that contribute to a nuclear physicists perception of 'natural.'

First and foremost, the spikes in whatever graph he was reading would obviously not be caused by anything natural, hence his expression when he sees it. If it were natural, he'd likely be shocked, but he wouldn't linger on it to watch it like that. At least, I don't think he would.

Another reason is because a natural disaster wouldn't isolate the plant. Whatever happened only took place at the plant and didn't affect the surrounding area (at least not greatly). If the scene with the ground having a drag mark on it is from the plant scene as well, then that is the other piece of evidence that something is amiss and unnatural becuase, let's face it, a natural disaster doesn't leave a drag mark in the ground.

So those are the two main things from the trailer specifically that I believe are going on to tell him it wasn't natural. Another possibility off the top of my head is that he might actually get a glimpse of whatever caused it through the smoke before it leaves, but since he can't see it clearly the governments and military pass it off as him hallucinating or going crazy due to the loss of his wife.