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

Pasadena, Calif.’s City Hall is seen Monday. Ryan Sun/AP

When nan 4.4-magnitude earthquake struck the Los Angeles area Monday afternoon, Angelenos reported a lengthy quake pinch important shaking.

But nan number attached to an earthquake only tells you truthful overmuch astir it. A assortment of different factors power really a quake is felt connected nan Earth’s surface, according to University of California, Berkeley Seismology Lab head Richard Allen.

“Even if it’s nan aforesaid magnitude, of people nan further you are distant from nan earthquake will person an effect, but besides nan benignant of sediments aliases rocks that you’re sitting connected will impact nan magnitude of shaking,” he says. “For that matter, moreover nan building you’re successful tin origin you to consciousness much shaking aliases little shaking.”

Magnitude describes a quake’s strength

Magnitude is nan measurement of nan spot of an earthquake, and it’s usually expressed utilizing nan Richter scale. Larger, longer-lasting earthquakes person higher magnitudes than smaller, shorter ones.

Your proximity to nan epicenter of an earthquake will apt find really powerfully you consciousness it: nan nearer you are, nan much aggravated it will be.

That’s not ever nan lawsuit though. For immoderate higher magnitude earthquakes, nan astir aggravated shaking is felt on nan responsibility statement wherever nan earthquake occurs, Allen says. That intends that 2 group arsenic acold from nan epicenter whitethorn consciousness shaking astatine different intensities if only 1 of them is on nan responsibility line.

If you’re successful a building erstwhile a quake strikes, nan type of building besides matters. Allen says one- aliases two-story buildings only amplify seismic shaking a small bit, while taller buildings and skyscrapers sorb overmuch much of a quake’s power and tin sway backmost and forth.

Soil plays a awesome domiciled successful earthquake intensity

City workers astatine correct representation retired nan installation of fencing astir earthquake damaged buildings Tuesday, Aug. 26, 2014, successful Napa, Calif. (Eric Risberg/AP)

The constitution of nan ungraded and rocks beneath you tin besides impact really beardown an earthquake feels.

People surviving successful sedimentary basins pinch soft soils acquisition much powerful shaking, because nan ungraded efficaciously amplifies nan seismic waves, while those located connected harder rocky surfaces whitethorn consciousness a weaker quake.

That’s because a activity entering ungraded is forced to slow down, “but nan number of peaks and troughs per 2nd has to enactment nan same,” Allen said. “The wave can’t change. The velocity has changed. And that intends that each nan power gets squished into a shorter wavelength, and that’s what gives you nan larger amplitude.”

Soft soils tin besides origin quakes to past longer by trapping power and making it bounce astir a sedimentary basin, expanding nan long of nan tremors.

“So if you are successful a sedimentary basin, you typically get larger amplitudes and you get longer long of nan shaking,” he said. “So it’s a spot of a double whammy.”

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

Intensity aside, waves tin besides consciousness different.

P waves — nan first ones that emanate from an earthquake — are often higher-frequency and tin consequence successful jerky shaking.

“And past nan S waves that travel later,” Allen said, “they typically are overmuch much gradual benignant of oscillations, and truthful it feels for illustration it’s that benignant of rolling sensation.”

People adjacent to nan epicenter of an earthquake typically consciousness nan much aggravated P waves, moreover though nan S waves come correct after them, according to nan U.S. Geological Survey. Those located farther distant from nan quake whitethorn only consciousness nan S waves that recreation much slowly.