Earthquakes and Seismic Waves

• Earth's crust is divided into moving plates that meet at fault lines, where earthquakes commonly occur.
• Earthquakes result from the plates rubbing, pressing, sliding against each other, causing surface vibrations.
• Seismic activity study the size, type and frequency of earthquakes

Measuring Earthquakes

• Earthquakes originate underground; seismographs measure ground-shaking activity on the surface.
• Seismographs are also called Seismometers.
• Seismometers have internal mass/pendulum attached to a spring, moving with ground movement.
• Seismograms are the recordings made by the seismograph.

Seismic Waves

• Seismic waves originate at the earthquake's center and radiate outward.

Body Waves

• Travel through the Earth's interior.
• P-waves (Primary waves) are fast, longitudinal compression waves.
• S-waves (Secondary waves) are slower, transverse waves that cause more damage.
• P-waves compress ground, while S-waves move in an up-and-down motion.
• S-waves travel only through solids and are absorbed by Earth's liquid outer core.

Surface Waves

• Cause the most damage and move along the Earth's surface.
• Love waves are the fastest, moving in a snake-like, horizontal motion.
• Rayleigh waves move like S-waves on the surface, causing significant shaking.

Measuring Earthquakes

• Seismograms help determine an earthquake's location, size, and strength (magnitude).

Richter Scale

• Developed in 1935 by Charles Richter.
• Uses the base-10 logarithm of the largest wave's amplitude on a seismograph.
• Each whole number increase represents a ten-fold increase in magnitude.
• Originally designed for magnitudes 3-7, now has a wider range.
• An earthquake measured at 6.1 is considered to be medium to strong.

Moment Magnitude Scale

• Preferred for high-magnitude earthquakes.
• Measures seismic movement, not just wave amplitude.
• Used to measure earthquakes higher than 8.
• Calculated using fault line information and seismic activity.