Earthquakes of the same magnitude can feel different. Here’s why

When the 4.4-magnitude earthquake struck the Los Angeles space Monday afternoon, Angelenos reported a prolonged quake with vital shaking.

However the quantity connected to an earthquake solely tells you a lot about it. Quite a lot of different elements affect how a quake is felt on the Earth’s floor, in accordance with College of California, Berkeley Seismology Lab director Richard Allen.

“Even when it’s the identical magnitude, after all the additional you’re away from the earthquake will have an impact, but additionally the form of sediments or rocks that you just’re sitting on will have an effect on the quantity of shaking,” he says. “For that matter, even the constructing you’re in could cause you to really feel extra shaking or much less shaking.”

Magnitude describes a quake’s power

Magnitude is the measurement of the power of an earthquake, and it’s often expressed utilizing the Richter Scale. Bigger, longer-lasting earthquakes have greater magnitudes than smaller, shorter ones.

Your proximity to the epicenter of an earthquake will possible decide how strongly you are feeling it: the nearer you’re, the extra intense it is going to be.

That’s not all the time the case although. For some greater magnitude earthquakes, essentially the most intense shaking is felt alongside the fault line the place the earthquake happens, Allen says. That signifies that two folks equally removed from the epicenter might really feel shaking at completely different intensities if solely considered one of them is alongside the fault line.

Should you’re in a constructing when a quake strikes, the kind of construction additionally issues. Allen says one- or two-story buildings solely amplify seismic shaking just a little bit, whereas taller buildings and skyscrapers take in rather more of a quake’s vitality and might sway backwards and forwards.

Soil performs a significant function in earthquake depth

The make-up of the soil and rocks beneath you may as well have an effect on how sturdy an earthquake feels.

Individuals dwelling in sedimentary basins with mushy soils expertise extra highly effective shaking, as a result of the soil successfully amplifies the seismic waves, whereas these positioned on tougher rocky surfaces might really feel a weaker quake.

That’s as a result of a wave getting into soil is compelled to decelerate, “however the variety of peaks and troughs per second has to remain the identical,” Allen stated. “The frequency can’t change. The rate has modified. And that signifies that all of the vitality will get squished right into a shorter wavelength, and that’s what provides you the bigger amplitude.”

Delicate soils can even trigger quakes to last more by trapping vitality and making it bounce round a sedimentary basin, growing the period of the tremors.

“So if you’re in a sedimentary basin, you sometimes get bigger amplitudes and also you get longer period of the shaking,” he stated. “So it’s a little bit of a double whammy.”

Jolting shakes or a rolling sensation? It’s a matter of waves

Depth apart, waves can even really feel completely different.

P waves — the primary ones that emanate from an earthquake — are sometimes higher-frequency and can lead to jerky shaking.

“After which the S waves that come later,” Allen stated, “they sometimes are rather more gradual kind of oscillations, and so it feels prefer it’s that kind of rolling sensation.”

Individuals near the epicenter of an earthquake sometimes really feel the extra intense P waves, despite the fact that the S waves come proper after them, in accordance with the U.S. Geological Survey. These positioned additional away from the quake might solely really feel the S waves that journey extra slowly.

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