Earthshaking Terminology

Aftershocks: low-magnitude earthquakes caused by crustal adjustments after a major earthquake
Earthquake: vibrations in the form of seismic (shock) waves, generated by a rapid release of energy caused by movements along fractures in Earth’s crust (faults)
Epicenter:  the projection of the focus up to Earth’s surface
Focus: the location of fault movement within Earth
Foreshocks:  low-magnitude earthquakes that precede larger ones; analogous to wood splintering prior to snapping
Magnitude:
measure of the amplitude of the largest wave recorded on a seismogram
Seismic Wave Frequency - very low frequency waves measured in Hertz (1 Hz = one cycle per second) in the range of 20 to 0.03 Hz; these frequencies produce low rumbles that are felt more than heard
Seismic Waves:
    1. Body Waves (can have direct and reflected components):
    A) P-Waves: Primary, compressional or “push-pull” waves; fast-moving waves that vibrate in the direction of transmission; pass through fluids
    B) S-Waves: Secondary or “shear” waves; are slower moving waves that vibrate perpendicular to the direction of transmission; these waves do not pass through fluids

    2. Surface Waves: (Love waves (L-Waves) and Rayleigh waves (R-Waves)) travel along the surface of Earth and cause the ground to move in waves leading to surface and structural damage associated with earthquakes

    3. Tsunami: seismic sea wave; results from vertical displacement of ocean floor during an earthquake; can cause great damage in coastal areas

Seismogram: data record of seismic activity, can be paper or digital
Seismograph: recording instrument for signals from the seismometer, usually includes a signal amplifier and frequency filter; seismographs include drum recorders with paper seismograms or computers with digital data files
Seismology: the study of seismic waves generated by earthquakes; these waves can travel along Earth’s surface as surface waves and they can travel subsurface through Earth’s interior as body waves
Seismometer: mechanical/electronic device for detecting seismic waves