Imagine if a plane were to land in San Francisco at the exact moment a major earthquake struck. What would that be like?

An earthquake is one of nature's most frightening events. We often assume the ground we walk on is stable and immovable, but an earthquake can instantly shatter this illusion with incredible force. Let's explore how earthquakes function to understand the potential chaos that could unfold as the plane lands.

Earthquake Image Collection

An earthquake is a seismic wave that travels through the earth's crust. In fact, a large truck passing by your house can create a small earthquake, causing vibrations in the ground. However, earthquakes are typically events that affect large areas, such as an entire city. While earthquakes can be triggered by events like volcanic eruptions or underground blasts, most natural earthquakes occur due to shifts in the earth's tectonic plates. This process is studied through the theory of plate tectonics.

To explain a variety of unusual phenomena on Earth, scientists introduced the concept of plate tectonics. This theory accounted for things like the noticeable movement of continents over time, the concentration of volcanic activity in specific areas, and the enormous ridges found at the ocean's floor. The basic premise is that the earth's outermost layer -- the lithosphere -- is composed of several plates that slide over the layer beneath it, called the asthenosphere. These plates interact at their boundaries, forming faults where blocks of rock on either side move in different directions.

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Fault lines are far more prone to earthquakes than other areas on Earth. The San Andreas Fault in California is one of the most famous examples. This fault, which marks the boundary between the Pacific oceanic plate and the North American continental plate, stretches over 650 miles (1,050 km) of land. San Francisco, along with its newly built international airport, is located near this fault.

When a sudden rupture or shift occurs in the earth's crust, the resulting energy spreads out as seismic waves, much like the ripples in a body of water when disturbed. Surface waves, a type of seismic wave, behave similarly to water waves -- they cause the earth's surface to move up and down, leading to significant destruction.

What action can the airport take?

In certain regions, the severe damage caused by earthquakes can be attributed to a process called liquefaction of the soil. When an earthquake shakes the ground violently, it can cause loose soil and sediments to behave like a liquid. This phenomenon makes buildings or homes built on such ground more susceptible to collapse. During the Loma Prieta earthquake, the main runway at Oakland International Airport experienced significant damage due to liquefaction, with cracks as wide as 3 feet appearing.

To improve its ability to withstand earthquakes, the new San Francisco International Airport incorporates several cutting-edge construction technologies. One such innovation involves the use of enormous ball bearings.

As demonstrated, airports situated in regions prone to earthquakes face various safety concerns, such as:

The 267 columns that bear the weight of the airport each rest on a 5-foot-diameter steel ball bearing. The ball sits inside a concave base that is anchored to the ground. If an earthquake occurs, the ground can shift up to 20 inches in any direction. The columns, which are mounted on the balls, move a bit less than this as they roll within their bases, effectively isolating the building from the ground’s movement. Once the earthquake ends, gravity pulls the columns back to their original position. This system safeguards the passengers waiting for departing flights, but how are those arriving flights affected?

As we've previously noted, runways can suffer significant damage from liquefaction, meaning that a plane landing shortly after an earthquake might face a hazardous runway. If the control tower detects the earthquake and can contact the pilot, the aircraft may be rerouted to avoid landing entirely. However, if a plane is landing just as the earthquake’s initial shock hits, there’s little cause for concern. The plane's landing gear is designed to absorb heavy shocks from rough landings, ensuring that passengers experience the earthquake in comfort.