99% of the Internet Runs Along the Ocean Floor
The word "cloud" might suggest that internet data flies through the air. In reality, approximately 99% of international internet traffic is transmitted through fiber optic cables laid on the ocean floor. Satellite communications account for only about 1%.
When you connect to an overseas server on IP Check-san, your data is literally crossing the Pacific or Atlantic ocean floor. This article dives deep into the remarkable world of undersea cables - the physical backbone of the internet.
The Scale - Enough Fiber Optic to Circle the Earth 30 Times
As of 2025, over 600 undersea cables are in operation worldwide, with a total length exceeding 1.3 million kilometers. The Earth's equatorial circumference is about 40,000 kilometers, so these cables could wrap around the planet more than 30 times.
These cables consist of dozens of hair-thin optical fibers bundled inside a tube just a few centimeters in diameter. The latest cables can transmit hundreds of terabits per second (Tbps). Netflix 4K streaming requires about 25 Mbps, so a single cable could support millions of simultaneous 4K video streams.
Major Undersea Cable Routes
- Trans-Pacific: Numerous cables connect Japan and the US. FASTER (Google-funded, 60 Tbps), JUPITER (Amazon-funded), and others. Japan's fast internet is partly due to being a hub for Pacific cables
- Trans-Atlantic: Connecting Europe and North America. MAREA (Microsoft/Facebook-funded, 200 Tbps) is the largest in the Atlantic
- Intra-Asia: SJC2, APG, and others. Singapore serves as the hub for Southeast Asia
- Africa circumnavigation: 2Africa (Meta-funded, 45,000 km total) circles the African continent, aiming to dramatically improve Africa's internet connectivity
Laying Undersea Cables - The Challenge of 8,000-Meter Depths
Undersea cables are laid by specialized cable ships. Only a few dozen of these vessels exist worldwide. They pay out cable from the stern while precisely positioning it along the ocean floor terrain.
Cable Structure
Undersea cables have different protective structures depending on depth.
- Shallow water (less than 1,000 m): Double-armored with steel wire to protect against fishing nets and anchors. About 5 cm in diameter
- Deep sea (over 1,000 m): Armor is omitted for weight reduction since physical threats are minimal. About 2 cm in diameter - roughly the thickness of a garden hose
- Optical fibers: Placed at the cable's core. The latest cables house 16-24 fiber pairs
- Repeaters (amplifiers): Installed every 60-100 km to amplify optical signals. Designed to withstand deep-sea pressure and last over 25 years
Cost of Installation
A single transoceanic cable costs hundreds of millions to over a billion dollars to install. In recent years, tech giants like Google, Meta, Microsoft, and Amazon have invested heavily in their own dedicated cables. By directly connecting their data centers, they achieve lower latency and guaranteed bandwidth.
Natural Enemies of Undersea Cables - Sharks, Anchors, and Earthquakes
Undersea cables experience approximately 100-200 faults per year. The causes include some surprising culprits.
1. Ship Anchors and Fishing Activity
The leading cause of cable faults is ship anchors and bottom trawling, accounting for about 60-70% of all incidents. In shallow waters, cables are buried 1-3 meters beneath the seabed for protection, but even this can't withstand a direct hit from a large ship's anchor.
2. Shark Bites
Cases of sharks biting undersea cables have actually been documented. One theory suggests sharks mistake the weak electromagnetic fields emitted by cables for prey, though the exact cause remains unknown. Google reportedly added Kevlar fiber protective layers to its Pacific cables in 2014. However, shark-related faults are a very small fraction of the total.
3. Earthquakes and Submarine Landslides
The 2006 earthquake off southern Taiwan caused submarine landslides that severed multiple undersea cables simultaneously, severely disrupting East Asian internet traffic for weeks. The 2011 Great East Japan Earthquake also damaged several cables on the Pacific side.
4. Intentional Sabotage
Undersea cables can also be military and geopolitical targets. During the Cold War, US submarines famously tapped Soviet undersea communication cables in "Operation Ivy Bells." More recently, suspicious damage to undersea cables has been reported in the Baltic Sea and off the coast of Norway, raising security concerns.
What Happens When a Cable Is Cut?
When a major undersea cable is severed, traffic is rerouted through other cables. The internet's routing protocol (BGP) automatically selects alternative paths, so in many cases, end users don't even notice the recovery. Similarly, DNS resolution continues to function through redundant servers, though response times may increase.
However, regions with low cable redundancy face serious consequences. Pacific island nations and parts of Africa that depend on just 1-2 cables can lose internet connectivity entirely when a cable is cut. During the 2022 Tonga volcanic eruption, the country's sole undersea cable was severed, isolating Tonga from the internet for approximately 5 weeks.
The Repair Process
Cable repairs are performed by specialized repair ships. They locate the fault, raise the cable from the seabed, cut out the damaged section, and splice in new cable. Deep-sea repairs can take days to weeks and cost millions of dollars per incident.
Undersea Cables and Latency - The Speed of Light Limit
The speed of light in optical fiber is about two-thirds of the speed of light in a vacuum (approximately 300,000 km/s), or about 200,000 km/s. The undersea cable distance from Tokyo to Los Angeles is about 9,000 km, so the one-way propagation time is approximately 45 milliseconds. Round trip: about 90 milliseconds. This is the physical lower bound of latency.
In practice, signal processing at repeaters, routing at landing stations, and processing at network equipment add to this, so the actual RTT (Round Trip Time) between Tokyo and Los Angeles is typically 100-120 milliseconds. When you check a connection to an overseas server on IP Check-san, you can feel this latency caused by physical distance. Understanding how IP addresses work helps explain why your traffic takes specific routes across these cables.
In the world of high-frequency trading (HFT), these few milliseconds can mean enormous profits, driving massive investment in the shortest-path undersea cables.
The Geopolitics of Undersea Cables
Undersea cables are critical infrastructure in 21st-century geopolitics.
- Data sovereignty: Concerns about national data transiting cables through other countries' territorial waters have made new cable route selection increasingly political. This is one reason why VPN usage has grown, as encrypted tunnels add a layer of protection regardless of which cables carry the data
- Tech giant influence: Google, Meta, Microsoft, and Amazon now account for the majority of new undersea cable investment. While telecom carrier consortiums once led the way, tech giants' private cable construction has surged
- Chokepoints: Geographic points where cables concentrate - around Egypt's Suez Canal, the Strait of Malacca, the Strait of Gibraltar - carry elevated risks of faults or attacks
Summary - The Invisible Infrastructure Powering Daily Life
At this very moment as you read this article, data is racing through optical fibers thousands of meters beneath the ocean. The reality of the "cloud" is cables just a few centimeters in diameter lying on the ocean floor, and pulses of light racing through them.
When you check your IP address and connection on IP Check-san, try imagining which undersea cable your data is traveling through. You can interactively explore the locations of undersea cables worldwide on TeleGeography's Submarine Cable Map (submarinecablemap.com).