bedrock: The thick, solid rock layer than underlies the soil and other broken, rocky materials on Earth’s surface.

civil engineer: An engineer who creates buildings, tunnels, water systems and other large projects that improve everyday life.

earthquake: A sudden and sometimes violent shaking of the ground, sometimes causing great destruction, as a result of movements within Earth’s crust or of volcanic action.

engineering: The field of research that uses math and science to solve practical problems. Someone who works in this field is known as an engineer.

factor: Something that plays a role in a particular condition or event; a contributor.

frequency: The number of times some periodic phenomenon occurs within a specified time interval.

geophysics: A field of science that applies and focuses on the principles of physics (energy and forces) to the study of Earth and to similar structures in other celestial bodies (such as exoplanets). People who work in this field are known as geophysicists.

magnitude: (in geology) A number used to describe the relative size of an earthquake. It runs from 1 to more than 8 and is calculated by the peak ground motion as recorded by seismographs. There are several magnitude scales. One of the more commonly used ones today is known as the moment magnitude. It’s based on the size of a fault (crack in Earth’s crust), how much the fault slips (moves) during a quake, and the energy force that was required to permit that movement. For each increase in magnitude, an earthquake produces 10 times more ground motion and releases about 32 times more energy. For perspective, a magnitude 8 quake can release energy equivalent to detonating 6 million tons of TNT.

mass: A number that shows how much an object resists speeding up or slowing down — basically a measure of how much matter that object is made from.

pyramid: A monumental structure with a square or triangular base and sloping sides that meet in a point at the top. The best known are those made from stone as royal tombs in ancient Egypt.

resonance: (in physics) The quality of being loud and clear, or, making sound by vibrating another thing. Or a term for some system in which an external stimulus has set up a large vibration of some kind, the frequency of which matches that of the stimulus.

risk: The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

stress: (in physics) Pressure or tension exerted on a material object.

subtle: Adjective for something that may be important, but can be hard to see or describe. For instance, the first cellular changes that signal the start of a cancer may be only subtly different — as in small and hard to distinguish from nearby healthy tissues.

vibrate: To rhythmically shake or to move continuously and rapidly back and forth.