Geological Faults that Tear the Earth Apart

An earthquake shaking the very foundations you live on would be jeopardy enough for most people to endure, but if upon stepping outside your home you were also to find massive fissures riddling the earth, cathedral-sized alarm bells would start ringing. Fear wouldn’t be the word. Cracks appearing in the ground during major seismic events is picture book stuff, but let’s see how they look for real, while considering the forces that cause them – and the effects they have.

Cracks pass several feet in front of a house, Loma Prieta earthquake, CA, 1989.

Caused chiefly by rupturing geological faults, naturally occurring earthquakes happen almost constantly in seismic danger zones around the globe such as California, Alaska, Japan and Indonesia. Stored energy in the earth’s crust is suddenly released as if an omnipotent entity were playing with an elastic band, and the seismic waves created ripples out from the epicentre, sometimes to devastating effect.

Crack in the ground: Great San Francisco earthquake of 1906.

Thankfully earthquakes of larger magnitudes happen less frequently, but when they do take place, they sure cause a scene. It is during these bigger quakes that folks are liable to themsleves start trembling as they witness the severe shaking that is one of the hallmarks of this natural hazard. And it is then that people are more likely to crack mentally as they see the ground beneath their feet begin to rip asunder.

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Huge cracks and a sunken hole in the highway: Denali earthquake, Alaska, 2002.

As well as being a near-legendary cataclysmic image, ground ruptures can have decidedly concrete effects, resulting in severe damage to buildings and other rigid structures. These breaks and dislodgements of the earth’s surface along a fault can be several metres in size during major tremors.

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More cracks from the Denali earthquake, Alaska, 2002.

Ground rupture is a particular risk for large engineering structures like dams, bridges and nuclear power stations, so existing faults need to be scrupulously mapped to pinpoint any that might break the surface during the structure’s lifespan.

The Bay Bridge Collapse: Loma Prieta earthquake, CA, 1989.

One of the disastrous tremors the famous San Andreas Fault was responsible for was the Loma Prieta earthquake of 1989. It measured 6.9 on the moment magnitude scale and lasted for around 15 seconds, killing 63 people, injuring 3,757, and leaving thousands more homeless.

The upper deck of the San Francisco-Oakland Bay Bridge collapsed onto the deck below it, while closer to the epicenter in the Santa Cruz Mountains, cracks yawned wide.

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Crack system that destroyed a driveway, Loma Prieta earthquake, CA, 1989.

The Loma Prieta earthquake is remembered as the first major American quake to be broadcast live on TV, as a baseball World Series Championship game was being televised.

Road rendered in two: Denali earthquake, Alaska, 2002.

An even more massive quake to shake America in recent years was Alaska’s 2002 Denali earthquake.

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Huge cracking and a hole in the highway.

Measuring 7.9 on the moment magnitude scale, the Denali earthquake in Alaska was the largest recorded on the mainland United States for more than 150 years and its shock was the strongest ever recorded in the Alaskan interior.

Cracked yet? Ground level changes.

Thanks to the remote location in which the Denali Earthquake in Alaska took place, there were no deaths and minimal injuries, though the severe damage on highways that crossed the fault line made driving dangerous or simply impossible.

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Image: Tubbi

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Yamabe Bridge: Chuetsu earthquake, Japan, 2004.

Moving off the American continent, Japan’s Chuetsu earthquake, which took place in 2004, was actually a series of three earthquakes, measuring between 5.9 and 6.9 on the Richter scale, followed by aftershocks that persisted for two weeks. It was the deadliest earthquake to impact on Japan for a decade, with 39 reported fatalities plus thousands injured. Transport networks were particularly hard hit: a train was derailed, bridges and tunnels were affected, and expressways were closed due to damage from ground rupture, landslides and other hazards.

Cracks in the ground: Nias earthquake, Indonesia, 2005.

In 2005, what was to become known as the Sumatra or Nias earthquake struck its Indonesian islands of the same names. A truly devastating seismic event, 1,300 people were killed by this tremor, whose literally earth-shattering moment magnitude measured roughly 8.7, making it the most powerful quake the world had seen since 1965. The earthquake lasted for two minutes in total, though there were eight major aftershocks in the twenty four hours that followed. Hundreds of buildings were obliterated.

On this evidence, it’s small wonder cracks in the ground have such apocalyptic associations.

Sources: 1, 2, 3, 4, 5

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