Here's an interesting video with zero useful commentary.
What you see here is liquefaction. (from Wikipedia, sorry, I'm in a hurry.)
The pressures generated during large earthquakes with many cycles of shaking can cause the liquefied sand and excess water to force its way to the ground surface from several metres below the ground. This is often observed as "sand boils" also called "sand blows" or "sand volcanoes" (as they appear to form small volcanic craters) at the ground surface. The phenomenon may incorporate both flow of already liquefied sand from a layer below ground, and a quicksand effect whereby upward flow of water initiates liquefaction in overlying non-liquefied sandy deposits due to buoyancy.Notice that the guy taking the video is nonchalant about this because aside from weird water coming up in the park and cracks moving around nothing dramatic is happening. That's because the buildings around him are not bearing on that fill soil. Modern engineering practices call for pilings to be driven through the soil to something that can support the weight. There's a picture on that Wikipedia page of buildings that fell when the ground liquified under them in the Niigata earthquake in 1964. That sort of thing motivated them to implement more expensive engineering solutions.