The movement of seismic waves reveals the structure of Earth’s interior

Scientists investigate Earth's interior by studying seismic waves

Scientists investigate Earth's interior by studying seismic wavesBelow Earth's atmosphere lies the crust, which extends to the Mohorovičić discontinuity between five and 20 miles below Earth's surface. Below the crust lies the mantle, the liquid-metal outer core, and the solid inner core, which surpasses 5,200 degrees Celsius (9,392 degrees Fahrenheit).

Differences in seismic wave speeds let scientists determine an earthquake’s location

Because primary waves are faster than secondary waves, seismic stations will detect longer gaps between these waves’ arrivals the farther an earthquake is. Calculating the distance to the earthquake from three stations allows its origin to be triangulated.

The four types of seismic waves are categorized as body or surface waves

Primary (P) and secondary (S) waves are compression and shear waves, respectively, and travel through Earth’s interior, though secondary waves only move through solids. These waves’ energy is converted into rolling Rayleigh or horizontal Love waves at the surface.

View maps of seafloor topography, earthquakes, and volcanic activity

Earthquakes and volcanoes are most common at plate boundaries, where moving plates interact. Mapping the locations of these events creates outlines for the different tectonic plates on Earth, whose movements can be tracked via GPS satellites.

Convection flows in Earth’s mantle drive the movement of tectonic plates

These processes transfer heat from Earth’s core to the surface via rising magma plumes, while cooler, denser rock falls into the mantle at rates similar to human fingernail growth. These rates are determined by combining seismic data with computer simulations to model Earth’s interior.

Variations in rock types contribute to uncertainty in earthquake predictions

Different rock types can withstand different amounts of stress before breaking and melt at different temperatures within Earth’s interior, preventing uniform modeling. The planet’s uneven mass distribution also creates variations in gravitational force, complicating mantle movement.

Earthquake early warning systems do not predict earthquakes

Systems like ShakeAlert® use a network of hundreds of ground sensors to detect earthquakes moments after they begin. Since seismic waves travel about 5 km/s, individuals may be notified of earthquakes before they feel the seismic activity has reached them.

The history of helioseismology, which studies seismic waves traveling within the sun

Following World War II, scientists began studying the sun's influence on radio waves, the most popular form of mass communication at the time. NASA missions to study the sun's interior have since helped develop explanations for various phenomena in its atmosphere and protect digital infrastructure.

Tsunamis are caused by sudden seafloor shifts displacing water

Earthquakes of magnitude 7.0 with hypocenters within 100 km of the seafloor can vertically shift large sections of the seafloor significantly. This seismic activity is more commonly found in subduction zones, where an oceanic plate sinks beneath a continental one.

The Richter scale was only intended to quantify Southern California earthquakes

The scale, designed to rate the energy of the largest seismic waves released by an earthquake, was calibrated to the region’s crust and mantle properties. Since the 1970s, seismologists have instead used the moment magnitude scale, which considers all waves of released energy.

Geological tremors on the moon provide evidence that it is shrinking

Apollo seismometers have collected moonquake data, which scientists have analyzed to map the moon's interior and reveal that fault slips producing tremors are the result of sublunar cooling and contraction. It also revealed that the moon's inner core is about 500 kilometers (311 miles) across.

According to general relativity, gravitational waves are ripples in spacetime

First detected a century after Albert Einstein predicted their existence, gravitational waves transmit information about cosmological events by altering the shape of spacetime. Like ripples in water, these waves travel outward and can be detected on Earth, even for objects that do not emit light, such as black holes.

Geodesists define sea level using gravity rather than the ocean's height

The sea level is not the same everywhere because the Earth isn't perfectly spherical or has a uniform composition and density. Earth's gravitational field is carefully measured to determine where the sea level would be, even in places with no water.

Boomerang earthquakes reverse direction and ripple back the way they came

Computer simulations show that rapid changes in friction along a fault where an earthquake has traveled for long distances can produce a smaller quake in the opposite direction. Data consistent with the phenomena has only been recorded a handful of times from 2011 to 2023.

Symmetric patterns of magnetic stripes seen on either side of mid-ocean ridges

The symmetry provides evidence of seafloor spreading, where new oceanic crust is created at mid-ocean ridges, which pushes older ocean crust away on either side. Matching the pattern to magnetized material in rocks on Earth’s surface provided a timeline of ocean floor recycling.

Tree rings can reveal centuries of environmental change and natural events

The width and shape of tree rings reflect yearly growth conditions like rainfall or snowfall. Scars in the rings can record disruptions such as fires, avalanches, or earthquakes, explaining when and how those events occurred.

Earth’s tilt and orbit cause the sun to create a figure-eight pattern

The shape—called an analemma—can be obtained by photographing the sun from the same location and time daily for a year. The Earth's eccentricity created the analemma's width, and its tilt shifts the sun's height in the sky over the seasons.

Physicists detect the sound of heat in superfluids, theorized since 1938

Referred to as "second sound," the flow of heat in a superfluid resembles a sound wave bouncing back and forth. The heat-mapping techniques used to make the detection may improve the study of neutron stars and superconductors.

Light echoes are expanding shells of reflected starlight

Just as sound waves reveal the location of obstacles by reflecting off them, pulses of light emitted by stars illuminate rings of interstellar dust, giving the appearance of ejected material as the light travels outward.

How scientists use data to anticipate the phases of the El Niño-Southern Oscillation

Sea-surface temperatures across various regions of the equatorial Pacific Ocean can be compared with ocean temperatures elsewhere in the tropics to identify anomalies that indicate where in the ENSO cycle Earth finds itself. The "Niño 3.4" region in particular—known as the Ocean Niño Index—is a key indicator of ENSO phase and intensity.

Stars appear to twinkle because turbulence in the motion of molecules in Earth's atmosphere causes light to bend and wiggle rapidly on its way to the surface—a phenomenon called scintillation.

Spectroscopy lets scientists analyze an object's light to determine its properties

By separating the light spectrum into its component wavelengths and comparing them to what is expected based on Earth-based experiments, we can determine an object's temperature, elemental and molecular composition, and motion through space.

Turtles' sense of direction comes from sensitivity to Earth's magnetic field and wave movement

Female sea turtles use this ability to migrate hundreds of kilometers across the ocean from their feeding grounds to the beaches where they were born to lay their eggs. Researchers have found that these turtles can reach these beaches despite ending up significantly off course as they detour away from predators or toward foraging territories.

The construction of LIGO needed to compensate for Earth's curvature

Across the 4-kilometer (2.5-mile) arms, the height of Earth's surface falls by almost a meter, preventing the lasers traveling within the arms from meeting the mirror at the end of each. Concrete slabs built beneath the arms help keep them level and provide structural support against seismic vibrations.

X-ray diffraction reveals atomic structures by analyzing how crystals scatter X-rays

X-ray diffraction involves rotating a crystal in an X-ray beam while a detector captures the resulting diffraction patterns, which depend on the crystal’s internal structure. The mathematical principles behind the technique won the 1915 Nobel Prize and improved crystallography.

View the quantum mechanical depiction of electrons as waves around the atomic nucleus

Unlike Bohr's fixed paths, the quantum model describes electrons as exhibiting behavior resembling standing waves—waves that have fixed points at the end while vibrating, like a plucked guitar string. Rather than determining their exact positions, only the probabilities of electrons being in a specific region can be determined.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Visualize the path of every solar eclipse from 1900 to 2099 and see what each looks like when observed from different locations on Earth.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

Explore the animals that populate the depths of the ocean, from fish and coral in the first few hundred feet, all the way down to the bottom of the Mariana Trench.

Waves off the coast of Nazaré, Portugal, can reach over 100 feet and are caused by the area's deep underwater canyon geography

Hurricanes, which rely on air consistently spinning in the same direction, cannot cross the equator because air curves in opposite directions north and south of it.

The boiling temperature of water decreases with increasing elevation because the molecules need less energy to overcome the lower atmospheric pressure associated with thinner air.

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

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Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

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Neutron stars, the remains of some massive stars after they explode in a supernova, are the densest directly observable objects in the universe.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

Recent research found that the brain doesn't seem to massively rewire following amputation—upending earlier beliefs about the cause of phantom limb pain.

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