The question of which city experiences the most earthquakes is complicated by how geologists define “most.” The sheer count of seismic events, which includes tremors too small to be felt, differs from the count of large, destructive quakes that pose a risk to urban populations. The location with the highest frequency of ground movement is typically situated where multiple tectonic plates are actively interacting.
How Seismic Activity is Measured
Measuring seismic activity requires distinguishing between the total energy released and the resulting ground shaking felt by people. Geologists use a device called a seismograph, which records the motion of the earth relative to a stationary mass. The resulting record, called a seismogram, provides the data needed to calculate an earthquake’s magnitude.
The modern standard for determining the energy released at the source of a quake is the Moment Magnitude Scale. This scale is logarithmic, meaning that each whole number increase represents about a 32-fold increase in the energy released. This is distinct from intensity scales, such as the Modified Mercalli Intensity scale, which measures the effects of shaking at a specific location, accounting for factors like distance from the epicenter and local geology. The city that records the highest frequency of tremors is often the one situated over the most active micro-faults and equipped with the most sensitive seismograph networks.
The City with the Highest Earthquake Frequency
Based on the number of recorded tremors, the metropolitan area of Tokyo, Japan, is one of the most seismically active urban regions globally. The greater Tokyo area is subject to frequent seismic activity because it sits at a complex, triple junction where four major tectonic plates meet: the Pacific Plate, the Philippine Sea Plate, the Eurasian Plate, and the North American Plate.
The Pacific Plate and the Philippine Sea Plate are both actively subducting, or diving beneath, the continental plates upon which the city rests. This geological process creates stress that is released through thousands of small to moderate quakes each year. While many of these events are low-magnitude and go unnoticed, they contribute to the city’s high frequency count. This constant movement also creates the potential for a catastrophic megathrust event caused by the sudden slip of the subducting plate.
Major Global Urban Seismic Hotspots
While Tokyo records a high volume of micro-quakes, other major urban centers generate fewer but often larger, more destructive events. The Pacific Ring of Fire, a horseshoe-shaped zone encircling the Pacific Ocean, accounts for approximately 90% of the world’s earthquakes. Cities like Santiago, Chile, lie along this ring where the Nazca oceanic plate is subducting beneath the South American continental plate, a process that has produced some of the largest recorded earthquakes.
In North America, the San Francisco Bay Area is situated along the transform boundary between the Pacific and North American plates. Movement along the San Andreas Fault system, where the plates slide horizontally past one another, causes frequent, moderate earthquakes and carries a high probability of a future large quake.
The second most seismically active region globally is the Alpide Belt, which stretches from Java to the Atlantic. This belt is the result of the collision of the African, Arabian, and Indian plates with the Eurasian plate. Major cities along the Alpide Belt, such as Istanbul, Turkey, and Kathmandu, Nepal, face high seismic risk from this convergent interaction.
Istanbul is close to the North Anatolian Fault, a strike-slip boundary with a history of large, westward-migrating earthquakes. The pressure from the Indian Plate pushing into the Eurasian Plate created the Himalayan mountain range, making Kathmandu highly vulnerable to destructive quakes. These cities demonstrate that a lower frequency of tremors can still correspond to a higher risk of major disaster.