Earthquakes generally start causing real damage at magnitude 5.5 and above, with anything magnitude 7.0 or higher considered a major, destructive event. But magnitude alone doesn’t tell the whole story. A shallow magnitude 6.0 earthquake directly beneath a city can be far more devastating than a deep magnitude 7.0 hundreds of miles away. Understanding where the key thresholds fall, and what other factors matter, helps you make sense of earthquake news when it happens.
Magnitude Levels and What They Mean
Earthquake magnitude is measured on a logarithmic scale, which means each whole number jump represents roughly 32 times more energy released. A magnitude 6.0 isn’t twice as strong as a 3.0. It’s thousands of times more powerful. Here’s how the scale breaks down in practical terms:
Below 2.5: These happen constantly around the world and almost never get felt by people. Seismographs pick them up, but you won’t notice one.
2.5 to 5.4: You’ll often feel these, especially at the higher end. They can rattle dishes, swing hanging objects, and crack weak plaster, but structural damage to buildings is rare. Most people experience these as a jolt or brief rolling sensation and move on with their day.
5.5 to 6.0: This is where things start to get serious. Earthquakes in this range cause slight damage to buildings and other structures, particularly older ones not built to modern standards. Windows can shatter, chimneys can crack, and poorly maintained walls may partially collapse.
6.1 to 6.9: These are strong earthquakes capable of causing significant damage across a populated area. In regions without earthquake-resistant construction, buildings can collapse and infrastructure like bridges and highways can fail.
7.0 to 7.9: These are classified as major earthquakes. They cause serious damage over large areas, can level poorly built neighborhoods, and disrupt utilities and transportation for weeks or months.
8.0 and above: These are “great” earthquakes. They can totally destroy communities near the epicenter and cause damage hundreds of miles from the source. The 2011 earthquake off the coast of Japan registered 9.1 and devastated coastal cities through both shaking and the tsunami that followed.
Why Two Earthquakes of the Same Magnitude Can Feel Completely Different
Magnitude measures the total energy released at the earthquake’s source, deep underground. It’s a single number for the entire event. But what you actually experience on the surface, the shaking, the noise, the damage, depends on a separate measurement called intensity. Intensity varies by location: people near the epicenter feel violent shaking while people 50 miles away might barely notice.
The U.S. uses the Modified Mercalli Intensity scale, which runs from I (not felt) to X (extreme destruction). A magnitude 6.5 earthquake might produce intensity VIII near the epicenter, with collapsed walls and fallen chimneys, while registering only intensity III twenty miles out, where people feel a slight tremor indoors. This is why earthquake reports often list both a magnitude and varying intensity levels across the affected region.
Depth Changes Everything
One of the most important factors in how destructive an earthquake becomes is how deep it occurs. Shallow earthquakes, those with large fault movement less than 3 kilometers below the surface, concentrate their energy where people live and build. Research on shallow destructive earthquakes has shown that quakes of similar magnitudes can produce dramatically different levels of ground shaking and damage depending on whether the fault slipped near the surface or deep underground.
A magnitude 5.8 earthquake at 5 kilometers deep beneath a city can crack foundations and bring down older buildings. The same magnitude at 100 kilometers deep might feel like a gentle sway. When you see earthquake reports, check the depth. Anything listed as “shallow” (typically under 70 kilometers, and especially under 20 kilometers) deserves more attention than a deep one of the same magnitude.
When Earthquakes Trigger Tsunamis
Earthquakes become a different kind of threat when they happen beneath or near the ocean floor. Not every undersea earthquake generates a tsunami. The quake needs to be large enough to physically push the ocean floor upward or downward, displacing the water column above it. This vertical movement of the seafloor is what sets a tsunami in motion.
The size of the displaced area, how long the rupture lasts, and the water depth at the source all determine whether a tsunami forms and how large it becomes. The 2004 Indian Ocean earthquake, magnitude 9.1, ruptured along roughly 800 miles of fault line about 19 miles below the ocean floor, displacing a massive volume of water and sending destructive waves across the entire Indian Ocean basin. Even earthquakes too small to directly generate a tsunami can trigger underwater landslides that produce one.
Building Standards and Location Matter
Where an earthquake hits matters as much as how strong it is. Modern seismic building codes require structures to absorb and dissipate energy during shaking without collapsing. Buildings in earthquake-prone regions like Japan, California, and Chile are designed to flex rather than break, using reinforced frames and flexible joints that let the structure move with the ground.
These codes are based on the most severe earthquake effects expected in a given area. Engineers design buildings to withstand two-thirds of the maximum considered earthquake for their location, with enough margin to prevent collapse even if shaking exceeds expectations. This is why a magnitude 7.0 earthquake in Tokyo, where strict codes have been enforced for decades, produces far fewer casualties than a magnitude 7.0 in a region with older, unreinforced construction. The 2010 Haiti earthquake was only magnitude 7.0, but it killed over 200,000 people largely because buildings weren’t designed to handle that level of shaking.
If you live in a seismically active area, the age and construction type of your building is one of the biggest factors in your personal risk. Unreinforced masonry, soft-story apartments (with open parking on the ground floor), and buildings on filled land or soft soil are the most vulnerable, even in moderate earthquakes in the 5.5 to 6.5 range.
How Often Do Dangerous Earthquakes Happen
The world experiences roughly 15 to 20 earthquakes of magnitude 7.0 or higher each year, and one or two at magnitude 8.0 or above. Magnitude 5.0 to 5.9 earthquakes happen more than a thousand times annually. The vast majority occur in remote areas or deep underground and never make the news. It’s the combination of a strong, shallow earthquake hitting a populated area that creates a disaster, and that combination is relatively rare for any single location, even along major fault lines.