Whales beach themselves from time to time. Mass beachings, too. Not just one whale who ate loco weed.
Earthquakes happen. How do we explain it? Well, see, it's like this. There are these tectonic plates that kind of "float" over the Earth's mantle. They move slower than glaciers, but they have lots and lots of that stuff we like to call "mass." When they go bump in the night, their power is so huge that they cause mountains to rise up. Mountain chains, even. True story. Now sometimes, along the fault zones where plates meet, the force is so powerful and stored so hard and so long, that occasionally the area along those fault lines break. SNAP! Of course, when something as massive as a tectonic plate makes the Earth's crust go "pop," the energy released is pretty damn powerful. And behold. Ye have Earthquakes.
They happen literally all the time. Once in a while, the stored energy is more violently released than others. And when that happens, it's like mother nature has declared war or something.
The world is full of mysteries. One thing we know is not a mystery is this planet X / Nibiru bullshit. It's not a mystery because it simply isn't true.