人間は地震を起こすことができるか? 誘発地震の真実

The Truth About Induced Seismicity: Can Humans Actually Cause Earthquakes?

The question sounds like it might itself be a myth — the idea that human activities could shake the earth seems to require an arrogance about human scale that geology routinely humbles. And yet the scientific evidence is unambiguous: certain human activities can and do cause earthquakes, sometimes damaging ones. This is not a myth to be debunked but rather a documented reality that requires careful explanation of mechanisms, scale, and context.

What Induced Seismicity Actually Means

[[Induced-seismicity]] refers to earthquakes caused or triggered by human activities that alter stress or pore pressure in the crust. The term covers a range of phenomena with different mechanisms, scales, and risk levels. The most significant source of induced seismicity in recent history has been the deep injection of wastewater — a byproduct of oil and gas production, particularly from hydraulic fracturing operations — into disposal wells. But induced seismicity also occurs from reservoir impoundment, mining, geothermal energy extraction, and carbon sequestration.

The Wastewater Injection Mechanism

Oil and gas production generates enormous volumes of briny water that must be disposed of. In the United States, much of this water is injected under high pressure into deep disposal wells, often into porous rock formations at depths of 1-3 kilometers. When high-pressure fluid is injected into rock, it reduces the effective normal stress on pre-existing 断層岩盤に沿って動きが生じた破断面。断層は数ミリメートルから数千キロメートルまで様々な長さがある。地震を引き起こす主要な断層は活断層と呼ばれる。 surfaces in the vicinity. This reduction in normal stress can allow a 固着断層摩擦によって動きが妨げられ、応力が蓄積している断層区間。固着断層がついに破壊すると、大地震を引き起こすことがある。 that was previously held in place by friction to slip, producing an earthquake. The 断層岩盤に沿って動きが生じた破断面。断層は数ミリメートルから数千キロメートルまで様々な長さがある。地震を引き起こす主要な断層は活断層と呼ばれる。 was already under tectonic stress sufficient to be near failure; the injection pressure change provides the final increment that triggers the event on a segment that was approaching its 地震再来間隔特定の断層における大地震と大地震の間の平均時間。古地震学や歴史記録から推定される。カスケード沈み込み帯の再来間隔は約500年である。.

Critically, the earthquakes are not occurring on the injection well itself but on nearby natural fault systems — sometimes 逆断層（スラスト断層）圧縮力によって、上盤が下盤に対して上方にずれる断層。傾斜の緩い逆断層（スラスト断層）は、最大級の地震の原因となる。 or 正断層断層面の上側の岩盤（上盤）が下側の岩盤に対して下方にずれる断層。リフト帯や発散型境界における引張力に関連して生じる。 structures — kilometers away from the injection point. The earthquake is releasing tectonic strain energy that was already stored — the injection merely advances the timing. This is why induced earthquakes can be larger than one might expect from a human activity: the energy comes from geological stress, not from the injection operation.

The Oklahoma Case Study

The most dramatic documented episode of induced seismicity in the US occurred in Oklahoma. From 1978 to 2008, Oklahoma recorded an average of about 1-2 M3.0+ earthquakes per year — a historically low rate consistent with its position far from active plate boundaries. Beginning around 2009, coinciding with a massive expansion in wastewater disposal well operations related to oil production from the Anadarko Basin, earthquake rates began rising sharply. By 2015, Oklahoma was recording over 900 M3.0+ earthquakes per year, briefly surpassing California as the most seismically active state in the contiguous US.

The largest event, the 2016 Pawnee earthquake at M5.8, caused damage and was clearly linked to nearby disposal wells through detailed analysis of well injection volumes, pressures, and the timing of seismicity. After Oklahoma regulators implemented traffic light protocols limiting injection volumes near known faults, earthquake rates declined sharply — providing causal confirmation that the wells were driving the seismicity. The 群発地震明確に卓越した本震を持たず、数日から数か月にわたって局地的な領域で発生する一連の地震。火山活動や流体の注入と関連することが多い。 behavior, with hundreds of small events clustering around specific injection wells, was a distinguishing signature.

Reservoir-Triggered Seismicity

Large dam reservoirs represent another well-documented cause of induced earthquakes. When a reservoir is filled, the weight of water (typically millions to billions of tonnes) increases stress on the underlying crust, while water percolating into rock pores increases pore pressure on faults. The combination has triggered significant earthquakes. The 2008 Sichuan earthquake in China (M7.9, nearly 90,000 deaths) remains controversial, with some researchers arguing that the Zipingpu Reservoir, filled in 2004, contributed to triggering the event on a pre-stressed fault by advancing its timing by decades. Whether this constitutes "causing" or merely "advancing" the earthquake is a philosophical distinction with enormous practical consequences.

The Koyna earthquake in India (M6.3, 1967) following impoundment of the Koyna Reservoir is a well-accepted example of reservoir-triggered seismicity. Several dozen cases worldwide are now documented where large reservoirs have triggered earthquakes up to M6+ magnitude.

Geothermal and Mining Seismicity

Geothermal energy extraction — circulating fluid through hot rock to generate electricity — involves both fluid injection and extraction that can alter subsurface stress. Several geothermal projects have been suspended or modified after inducing felt earthquakes. A geothermal project in Basel, Switzerland, was halted in 2006 after a M3.4 earthquake. Deep mining operations remove rock mass and alter stress in ways that can trigger 群発地震明確に卓越した本震を持たず、数日から数か月にわたって局地的な領域で発生する一連の地震。火山活動や流体の注入と関連することが多い。 activity and occasionally larger events in mines themselves.

The Scale Question: How Large Can Induced Events Get?

A common misconception is that induced earthquakes are always small nuisance events. While most are below M3.0 and not felt, the record shows events up to M5.8 (Oklahoma) from wastewater injection, and the question of whether M7+ events could be triggered remains a subject of active research. Some researchers argue that induced seismicity on critically stressed faults could potentially advance large tectonic earthquakes, though demonstrating this rigorously requires counterfactual reasoning about earthquake timing that is scientifically challenging.

The conservative regulatory approach — assuming that any fault in the vicinity of injection operations could be activated — is motivated by the asymmetric consequences: the cost of being overcautious with injection operations is much smaller than the cost of triggering a damaging earthquake.

Distinguishing Myth from Reality

The myth embedded in this topic is not "humans can't cause earthquakes" — they clearly can. The myths to be careful about are: that all modern seismicity is human-caused (the vast majority of earthquakes globally are purely tectonic), that induced earthquakes are always small and harmless (they can be damaging), and that technology will let us "design" earthquakes for stress relief (this remains speculative and potentially dangerous). The reality is more nuanced: specific human activities can induce seismicity under specific geological conditions, the risks can be assessed and managed with proper monitoring and regulation, and the phenomenon is now well enough understood to be incorporated into responsible energy and water management policy.

Use the Seismic Risk Checker to understand whether your location is in an area with documented induced seismicity concerns, alongside natural tectonic hazard.