Residents in the Northeast were shaken on Friday by a 4.8-magnitude earthquake centered near Lebanon, New Jersey. The tremors were felt as far as Baltimore and the Massachusetts-New Hampshire border, causing worry among workers in office buildings and residents who experienced the ground moving beneath them. However, no life-threatening injuries or significant damage have been reported so far.

The Richter scale, which was developed by Charles F. Richter in the 1930s, is no longer widely used. As more seismograph stations were installed around the world to measure earthquake sizes, it became apparent that Richter's method was valid only for specific distance and frequency ranges. Seismometers, instruments used to record ground motion, are now used to measure magnitudes, which indicate the size of an earthquake. These magnitudes range from 2.5 or less, which are usually not felt, to 8.0 or higher, which can cause significant damage.

While earthquakes that are large enough to be felt by a large number of people are relatively uncommon on the East Coast, there have been about 20 quakes above a magnitude of 4.5 since 1950, according to the United States Geological Survey. In comparison, the West Coast has experienced over 1,000 such earthquakes during the same period.

Jessica Thompson Jobe, from the USGS' Earthquake Hazards Program, emphasized that similar-sized earthquakes have been recorded in the New York region over the past few centuries. In 2011, a 5.8 magnitude earthquake near Mineral, Virginia, sent shockwaves across the East Coast, affecting a wide area from Georgia to Maine and even southeastern Canada. It was hailed as one of the most widely felt quakes in North American history, causing $200 to $300 million in property damages, including to the Washington Monument in Washington, D.C.

Unlike the West Coast, where earthquakes occur more frequently due to the rubbing of sections of Earth's crust, East Coast earthquakes like the one experienced on Friday are caused by the gradual compression of hard, brittle rocks deep underground. This slow compression is akin to cranking up a vise on a block of ice, eventually leading to cracks and rattling. The colder and harder rocks on the East Coast are better at spreading the energy from an earthquake, resulting in a broader area being affected.

The densely populated cities along the East Coast increase the likelihood of more people experiencing the effects of an earthquake. Leslie Sonder, a geophysicist at Dartmouth College, pointed out that the presence of population centers over a large part of the northeast contributes to the high number of people feeling these quakes.

USGS experts have warned of possible aftershocks for weeks to months, which are typical after any earthquake. They urge residents to stay alert and pay attention to emergency messaging from local officials. To stay safe during an earthquake, it is recommended to remove any furniture or objects from near sleeping areas that could potentially fall and cause harm. If shaking is felt, individuals are advised to drop to the ground, cover their head and neck with one arm, and seek shelter under a table if available. If no shelter is nearby, it is important to protect the head and neck by grasping them with both hands until the shaking subsides.