Why do earthquakes in the US do not shake the streets?

While people in high-rise buildings in New York City rushed out by earthquakes, many people on the street did not understand what was happening.

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The seismic shocks that shook the east coast of the United States yesterday had a magnitude of 5.9 Richter - the strongest in over 100 years. The earthquake shook Washington DC within 30 seconds, causing the buildings to shake. In New York City and many other places, buildings also shake, but the streets are not.

Hundreds of people fled to the streets of Philadelphia,
Pennsylvania, USA after the earthquake on August 23. (Photo: AP)

Livescience said, strong earthquakes rarely occur on the east coast of the United States, so scientists do not know much about their characteristics. Therefore they could not say exactly a normal or abnormal earthquake.

The crust in the eastern states is denser and colder than the crust in the western states. Therefore, seismic waves tend to spread further in the east.

'If an earthquake happens around Virginia state (east), seismic waves will spread to a larger area than when it happened in California state (west),' said Professor Jack Moehle, explained a construction expert at the University of California in the US.

That might have caused buildings, not streets, to shake in New York, an eastern city. The more seismic waves spread, the lower their frequency and vice versa.

'Waves with large wavelengths will make building vibrations easier than high frequency waves. So people on the ground may not sense waves with large wavelengths, but wave resonance effects in buildings make people in them feel earthquakes , 'Moehle said.