aftershocks - earthquakes of lesser intensity than the main shock. They may occur minutes, hours, days, weeks, or years after the first quake. anticline - an upward fold in rock. convection - is the heat transfer involving the movement of fluids—liquids and gases. During convection, heated particles of fluid begin to flow, transferring heat energy from one part of the fluid to another. When a liquid or gas is heated, the particles move faster. As the particles move faster, they spread apart. Because they are farther apart, they occupy more space. The density decreases. convection current - is the flow that transfers heat within a fluid. The heat from the earth's mantle and core causes convection currents to form in the astenosphere and throughout the mantle. The heating and cooling of the fluid, changes in the fluid's density, and the force of gravity combine to set convection currents in motion. epicenter - the point on the earth's surface directly over the focus. fault - a break in the earth's crust where slabs of rock slip past each other. fold - a bend in rock that forms where part of the earth's crust is compressed. During folding, the stress can cause an anticline (ground mounds upward) or a syncline (ground sinks downward). liquefaction - is a process by which water-saturated sediment temporarily loses strength and acts as a fluid, like when you wiggle your toes in the wet sand near the water at the beach. This effect can be caused by earthquake shaking. lithosphere - the outer solid part of the earth, including the crust and uppermost mantle. The lithosphere is about 100 km thick, although its thickness is age-dependent. The lithosphere below the crust is brittle enough at some locations to produce earthquakes by faulting. magnitude - measurement of energy released by an earthquake; maximum motion shown on a seismograph. normal fault - occurs when the two sides of a fault pull apart. The rocks on one side drop down lower than the other side. This is the result of two divergent boundaries undergo
tensional stress, causing the rock to break and slide downwards. seismograph - an instrument that detects and records the intensity, direction, and duration of earthquakes. stress - the force applied to an object. In geology, stress is the force per unit area acting on a rock. There are three types of stress: compression (squeezing), tension (stretching), and shear (twisting). subduction zone - a region where one tectonic plate is forced underneath another. Subduction zones are typically characterized by deep oceanic trenches and volcanic arcs. syncline - a downward fold in rock. tectonic plates - large, rigid pieces of the earth's lithosphere that fit together like a jigsaw puzzle. These plates are in constant motion, moving apart at divergent boundaries, colliding at convergent boundaries, or sliding past each other at transform boundaries. tsunami - a series of large ocean waves caused by the sudden displacement of a large volume of water. Tsunamis are often triggered by underwater earthquakes or volcanic eruptions. transform boundary - a type of plate boundary where two tectonic plates slide horizontally past each other. This motion can cause earthquakes. volcano - a vent in the earth's crust through which molten rock, ash, and gases are ejected. Volcanoes can be explosive or effusive, depending on the type of eruption.
