Seismic waves are an inherent part of the geology of our planet, serving as key pointers toward the internal structure of the Earth and the dynamics of earthquakes. Scientists, engineers, and individuals interested in seismology and the way the Earth behaves during seismic activities need to know about seismic waves. This blog addresses seismic waves, types of seismic waves, how they travel within the Earth, and how they assist us in knowing earthquake magnitude and intensity.
Seismic waves are energy waves traveling within the Earth and are mostly caused by geologic activities such as earthquakes, volcanic eruptions, and man-made activities like explosions. Seismic waves are caused by stress accumulation in the Earth's crust being released all at once and making other materials in the geology transmit vibrations.
Seismic waves consist of two broad types: body waves and surface waves. The body waves travel within the Earth, whereas surface waves move on the Earth's surface. These wave properties describe the structure and seismicity of the Earth.
Body waves, too, are divided into two: P waves (primary waves) and S waves (secondary waves).
P Waves (Primary Waves)
P waves are the fastest seismic waves, with velocities of approximately 5 to 8 kilometers per second (approximately 3 to 5 miles per second) in the crust of the Earth. P waves are compressional waves, i.e., they result in particles in the material through which they pass to move in opposite directions along the same line as the wave. This makes the material compress and expand, so P waves can pass through solids, liquids, and gases.
Because of their velocity, P waves arrive first and can be recorded by seismographs during an earthquake. Because they can travel through all materials, P waves are extremely useful in learning about the internal structure of the Earth. As a P wave travels to a boundary between two materials, like between the crust and the mantle, it slows down and refracts, giving us information on the contents of the layers of the Earth.
S Waves (Secondary Waves)
S waves travel more slowly than P waves at speeds of roughly 3 to 4.5 kilometers per second (roughly 1.8 to 2.8 miles per second). S waves are shear waves, whereas P waves are not. Shear waves result in particles oscillating perpendicular to the direction that the wave travels. This side-to-side movement produces a side-to-side shaking effect.
S waves can only propagate in solids, which is very important in seismology. The fact that S waves cannot travel through liquids means the outer core of the Earth must be liquid. The fact that S waves arrive later than P waves during an earthquake gives valuable information about the layers inside the Earth.
Surface waves travel on the surface of the Earth and usually have more significant amplitudes and longer lengths compared to body waves. Two prominent types of surface waves are Love waves and Rayleigh waves.
Love Waves
Love waves produce horizontal shaking, displacing the ground back and forth. They are the most rapid kind of surface wave and can be especially destructive in an earthquake because of their horizontal motion.
Rayleigh Waves
Rayleigh waves give rise to elliptical motion, and the ground both moves and oscillates vertically as well as horizontally, just like ocean waves. They usually lead to large ground shaking and are the main perpetrators of damage in an earthquake.
Seismic waves move at different speeds inside the Earth based on the material they are passing through. The way they behave when meeting geological materials, for instance, rocks, soil, and liquids, is vastly different.
Seismologists use highly developed instruments such as seismographs for detecting and recording seismic waves. These instruments measure the amplitude and frequency of seismic waves, assist scientists in locating earthquake epicenters, and know the wave velocity. Seismic monitoring continues to be conducted almost in perpetuity for research into tectonic movements, for the assessment of possible hazards, and to fine-tune early warning systems in earthquake-prone areas.
Seismic waves are used in the comprehension of earthquake magnitude and intensity, which are necessary to evaluate the probable effect of an earthquake.
The intensity of an earthquake is a measure of the impact of an earthquake at certain points, detailing the amount of shaking experienced and the damage caused. The Modified Mercalli Intensity (MMI) scale is generally employed to classify earthquake intensity from I (not felt) to XII (complete destruction). Intensity changes with several parameters such as distance from the epicenter, local geology, and construction types.
Seismic waves are very important in measuring intensity since the various types of waves have different impacts on the ground. P waves, for instance, will not necessarily do much damage, but S waves and surface waves tend to generate strong shaking and destruction.
Earthquake magnitude measures the energy released in an earthquake. The most common scales are the Richter scale and the moment magnitude scale (Mw). The moment magnitude scale is currently used as the norm for measuring large earthquakes because it better represents the size of an earthquake, considering the area of the fault that ruptured and the amount of slip.
Seismic waves are used to compute magnitude. Seismographs measure the amplitude of seismic waves, and scientists can determine the magnitude of the earthquake from these measurements. Every rise by one unit on the magnitude scale is equivalent to a tenfold rise in measured amplitude and about 31.6 times greater energy release.
Seismology, the observation of seismic waves and their impacts, is key to comprehending the Earth and enhancing our capability to react to earthquakes. Seismologists examine seismic data to:
Seismic waves are a critical component of learning about the internal dynamics of the Earth and the nature of earthquakes. From the observation of P waves, S waves, and surface waves, researchers can learn about the structure of the Earth and the character of seismic activity. Not only does this improve our knowledge of geology, but it is also an important factor in determining earthquake intensity and magnitude, which ultimately helps in disaster mitigation and risk reduction. As technology gets better, so will our means of analyzing and reacting to seismic activity, promoting a more secure environment for societies across the globe.
This content was created by AI