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The Myth: Earthquakes Are Getting Stronger

Related to but distinct from the "earthquakes are becoming more frequent" myth is the claim that individual earthquakes are becoming more powerful — that climate change, nuclear testing, or some other human or environmental force is intensifying the maximum magnitude of earthquakes. This myth surfaces particularly after major events, when commentators sometimes suggest the extreme magnitude reflects an escalating planetary crisis. The physics of Moment Magnitude ScaleThe modern standard for measuring earthquake size (Mw), based on the seismic moment — the product of fault area, average slip, and rock rigidity. Accurate for all earthquake sizes. and the geological record provide a clear answer, though some nuances deserve careful treatment.

How Earthquake Magnitude Is Measured

Modern earthquake magnitude is measured primarily through the Moment Magnitude ScaleThe modern standard for measuring earthquake size (Mw), based on the seismic moment — the product of fault area, average slip, and rock rigidity. Accurate for all earthquake sizes. scale (Mw), which was developed in the 1970s to overcome limitations of Charles Richter's original Richter ScaleThe original logarithmic magnitude scale developed by Charles Richter in 1935 to measure local earthquake magnitude. Largely replaced by moment magnitude but still commonly referenced in media. and is now the standard for large earthquakes. The moment magnitude is derived from the Seismic MomentA measure of the total energy released by an earthquake, calculated as the product of the fault area, average displacement, and the shear modulus of the rocks. The basis of moment magnitude. — the product of the shear modulus of the rock, the area of the fault that ruptured, and the average slip across that area. It is a measure of the total energy radiated as seismic waves.

The moment magnitude scale is logarithmic: each unit increase represents about 32 times more energy. A M9.0 earthquake like the 2011 Tohoku event releases approximately 32 times more energy than a M8.0 event, and about 1,000 times more energy than a M7.0 event. The largest earthquakes ever recorded (estimated M9.4-9.6 for the 1960 Valdivia, Chile, earthquake) are bounded by the maximum fault dimensions physically possible on Earth.

What Determines Maximum Earthquake Magnitude

The maximum possible earthquake magnitude on any given fault system is determined by the physical dimensions of the fault. Fault rupture cannot exceed the length of the fault segment, the width (depth extent) of the seismogenic zone, and the amount of accumulated slip. For the largest subduction zones — like the Cascadia Subduction Zone, the Japan Trench, or the South American subduction zone — rupture lengths of 1,000+ km are possible, enabling M9+ events. For strike-slip faults like the San Andreas, the geometry limits maximum magnitude to approximately M8.0-8.5. These limits are set by geology and physics, not by time period.

The Gutenberg-Richter LawA statistical law describing the relationship between earthquake frequency and magnitude: for each unit increase in magnitude, earthquakes become about 10 times less frequent. relationship describes the frequency-magnitude distribution of earthquakes in any region: for each unit of magnitude increase, frequency decreases by roughly a factor of 10. The slope of this relationship (the b-value) and the maximum magnitude are properties of the fault system determined by geology. They do not change on human timescales in response to climate, nuclear testing, or any other human activity.

The Historical Record vs. Instrumental Period

The Seismic NetworkA coordinated group of seismograph stations that continuously monitor earthquake activity. The Global Seismographic Network (GSN) includes 150+ stations providing worldwide coverage. that provides consistent global monitoring of earthquakes only achieved modern global coverage in the 1960s-1970s. Before this period, earthquake catalogs become increasingly incomplete as you go further back in time. This creates an observational artifact: the largest recorded earthquakes in the modern era (1960 Chile M9.5, 1964 Alaska M9.2, 2004 Indian Ocean M9.2, 2011 Japan M9.0) could create the impression that the most extreme events are recent phenomena.

But this apparent concentration of extreme events in the modern era largely reflects improved detection and recording. [[Paleoseismology]] — the study of prehistoric earthquakes from geological evidence — reveals that M8-9+ events have occurred repeatedly throughout geological history on the same fault systems we observe today. Japanese historical records document major tsunamis and earthquakes consistent with M9-class Tohoku-type events going back many centuries. The sediment record of the Cascadia Subduction Zone shows complete M9 ruptures occurring roughly every 200-500 years for thousands of years.

Why the Modern Instrumental Period Looks Extreme

The four M9.0+ events since 1960 (Chile 1960, Alaska 1964, Indian Ocean 2004, Tohoku 2011) might suggest a modern clustering of extreme events. Seismologists have examined this question carefully. The global rate of M9+ events in the instrumental era (approximately 1 per 20 years) is broadly consistent with geological estimates of recurrence intervals, though the clustering of large events in a 60-year window is on the high side of expected variability. This is within the expected natural randomness of a Poisson process with rare events — four events in 60 years is unusual but not statistically implausible given a 20-year mean recurrence.

Climate Change and Earthquake Magnitude

A common contemporary version of the myth is that climate change is making earthquakes stronger. There is no credible mechanism by which atmospheric warming could increase the maximum magnitude of tectonic earthquakes, and no evidence that it does. Tectonic earthquake magnitude is determined by fault geometry and accumulated strain, not by surface conditions.

However, there are legitimate research questions about climate-earthquake interactions at much smaller scales and longer timescales. Deglaciation — the melting of major ice sheets — changes the load on the crust and can affect seismicity rates over centuries to millennia as the crust rebounds (isostatic rebound). Some researchers have hypothesized that accelerated glacial melting could affect seismicity in formerly glaciated regions (Scandinavia, Iceland, Alaska) over coming decades to centuries, though the magnitudes involved are far smaller than the scale of effects implied by popular claims.

The Role of Seismic NetworkA coordinated group of seismograph stations that continuously monitor earthquake activity. The Global Seismographic Network (GSN) includes 150+ stations providing worldwide coverage. Improvements

The same monitoring improvements that make it appear more earthquakes are occurring (as discussed in the "earthquakes more frequent" guide) also affect the apparent record for large events. Better Seismic NetworkA coordinated group of seismograph stations that continuously monitor earthquake activity. The Global Seismographic Network (GSN) includes 150+ stations providing worldwide coverage. coverage means that earthquakes that would have been assigned lower magnitudes due to incomplete waveform data in the 1960s might be assessed at higher magnitudes today. Some upward revisions of historical earthquake magnitudes are the result of reanalysis using modern methods, not actual stronger shaking.

The Sumatra 2004 earthquake was initially reported as M9.0, then revised upward to M9.2-9.3 as more data became available and more complete waveform analysis was applied. This reflects improved methodology, not escalating seismicity.

What Is Genuinely Changing

While tectonic earthquake maximum magnitude is not changing, the consequences of earthquakes of a given magnitude are changing — upward. Growing population in coastal and seismically active zones, increasing urbanization in regions with inadequate Seismic DesignThe practice of designing structures to withstand earthquake forces. Modern seismic design aims to prevent collapse and protect life, while accepting some structural damage in major earthquakes. standards, aging infrastructure, and global supply chain interdependencies mean that a M7.8 earthquake in 2026 affects far more people and causes far greater economic disruption than a comparable event in 1926. This is a genuine and serious trend, but it reflects human vulnerability, not geological escalation.

The appropriate response is investing in Seismic RetrofitStrengthening an existing building to improve its earthquake resistance. Common methods include adding steel bracing, reinforcing foundations, and bolting structures to foundations. programs, updating building codes in rapidly urbanizing developing nations, improving Earthquake Early Warning (EEW)A system that detects an earthquake and sends alerts to people and systems before strong shaking arrives. Can provide seconds to tens of seconds of warning, enough to take protective action. infrastructure, and building institutional capacity for post-earthquake response — not alarm about inherently increasing earthquake power. The earth's geology is not conspiring against us; we are making choices about where and how we build that determine how consequential each earthquake becomes.