What are the layers of the solid Earth?
The solid Earth is divided into three main layers based on chemical composition: the crust, mantle, and core. The crust is the outermost, thin rocky skin. Beneath it lies the mantle, a hot, dense layer of silicate rock that behaves like a viscous fluid over geological time. At the center is the core, consisting of a liquid outer core and a solid inner core, both composed primarily of iron and nickel.
What are the properties of a solid?
A solid is a state of matter characterized by a structural rigidity and a resistance to a force applied to the surface. Unlike liquids or gases, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it. The atoms or molecules within a solid are tightly packed together and bound by strong intermolecular forces, vibrating only in fixed positions. This ordered arrangement gives solids a definite shape, a fixed volume, and high density.
What are the properties of a liquid?
A liquid is a state of matter with a definite volume but no fixed shape, allowing it to flow and conform to the contours of its container. Its atoms or molecules are closely packed—giving it a high density and making it nearly incompressible—but they possess enough kinetic energy to break bonds and slide past one another fluidly. This molecular mobility enables liquids to exhibit unique physical properties, including surface tension, viscosity, and capillary action.
What are primary earthquake waves?
Primary waves (P-waves) are the fastest seismic waves generated by an earthquake, making them the first to register on seismographs. These longitudinal, compressional waves travel by pushing and pulling the ground in the same direction the wave is moving. Because they compress and expand the material they pass through, P-waves can travel through all states of matter, including solid rock and liquid magma, altering their velocity as material density changes deep within the Earth.
What are secondary earthquake waves?
Secondary waves (S-waves) are the second type of seismic wave to arrive at a monitoring station during an earthquake. Operating as transverse or shear waves, they move the ground up and down or side to side, perpendicular to the direction the wave is traveling. Unlike P-waves, S-waves can only propagate through solid materials. Because liquids lack shear strength, S-waves are completely blocked by Earth's liquid outer core, creating a massive seismic shadow zone.
What are surface earthquake waves?
Surface waves are the slowest seismic waves generated by an earthquake, arriving long after P-waves and S-waves. Traveling exclusively along Earth’s outer crust rather than through its interior, they cause the most intense ground displacement. These waves move the earth in a rolling, elliptical motion or a jagged, side-to-side sway. Because their energy is concentrated at the surface, they are responsible for the severe shaking and catastrophic structural damage associated with major earthquakes.
What is a seismograph?
A seismograph is an instrument used to detect, measure, and record the ground motion caused by seismic waves from earthquakes or explosions. It operates on the principle of inertia: a heavy mass remains stationary while the surrounding frame moves with the shaking ground. This relative motion is recorded—traditionally by a pen on a rotating drum, but now digitally. The resulting data, a seismogram, reveals the earthquake's magnitude, distance, and exact arrival times of different waves.
The image below shows a sample seismogram.
A massive earthquake has struck an island in the Pacific. Seismograph stations worldwide have captured the resulting body waves, but the data contains an anomaly: stations located between 105° and 140° from the epicenter recorded absolutely no direct P-waves or S-waves, while stations beyond 140° recorded P-waves but completely lost the S-waves. Your challenge is to use this seismic data to map the interior structure of the solid Earth.)
