On May 5th 2024, a 4.8 magnitude earthquake shook New Jersey. It was the first sizeable quake the region had seen in years, and it made headlines across the US. What struck me, though, was how different the response was compared to the west coast, where quakes of that size happen fairly often without much fuss.
That contrast became the focus of a SciShow episode I wrote recently. On the surface, a 4.8 is a 4.8, no matter where it happens. But as I dug into the research, I was reminded that geology has a way of complicating even the neatest numbers.
The Richter scale, devised back in 1935, gave us a standard way of measuring quakes, but it was built on data from California and never really worked worldwide. These days, scientists use moment magnitude instead. It’s a more robust calculation that takes into account the properties of the rocks and the fault itself. Still, even that number can’t tell you everything about what an earthquake will feel like.
The real story is in the rocks. On the east coast, the crust is old, dense, and continuous, so seismic energy can travel astonishing distances. That’s why a 5.8 quake in Virginia in 2011 was felt almost 1,000 kilometers away, while a stronger quake in California barely carried half as far.
Then there’s the effect of what’s underfoot. If you’re standing on solid bedrock, the shaking might feel sharp but brief. But if you’re on softer sediments, the waves get amplified and drawn out. Mexico City, Christchurch, Los Angeles, all cities built on basins and old lakebeds, have all suffered devastating consequences from this “jello effect.”
One of the most fascinating (and sobering) examples I came across was the 2001 Gujarat earthquake in India. It measured 7.7 in magnitude and was felt over 1,000 kilometers away, causing tens of thousands of deaths. Just three years later, the enormous Sumatra-Andaman quake struck with a magnitude over 9. While it unleashed a catastrophic tsunami, the shaking itself wasn’t felt nearly as far afield. Same planet, same process, but completely different outcomes because of local geology.
Writing this episode was a good reminder that magnitude isn’t the whole story. Whether an earthquake feels like a distant rumble or topples buildings depends on the deep, complicated history written into the rocks beneath us.
Watch the full video here:
Leila Battison 
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