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This can’t be done from studying seismic waves alone, it requires a lot of local geology input and external considerations (for instance, earthquakes can also cause indirect damage though processes such as landslides) - but seismology is the first step. Naturally, this leads to the next reason for studying seismic earthquakes.Īssessing hazards basically aims to predict the potential ground shaking intensity from future earthquakes. Contrary to popular belief, the epicenter is not the place where the earthquake ruptures (that’s called the ‘hypocenter’), but rather is the projection of the earthquake on the surface, which can of course also be inferred from this data.Ī depiction of how an earthquake is “felt” at different distances and in different geological structures.Ī historical map of epicenters gives a good starting point to assess the likelihood of future earthquakes and can serve as a basic preparation, allowing city planners and residents to prepare for the likelihood of seismic events. Because the different waves have different speeds, by detecting the arrival times at in different regions in the world, the position of the earthquake can be detected - the so-called hypocenter. There are numerous seismographs around the world, all of which measure the earthquake (seismic) waves to some extent. If you detect an earthquake in at least three different locations, you can triangulate where the epicenter is. Studying and understanding seismic waves is more than a theoretical pursuit - it’s very important for a number of reasons, which flow quite logically. Love waves have a transversal (perpendicular) movement and are the most destructive outside the immediate area of the epicenter. Contrary to their name, there’s nothing really lovable about the Love waves - they were named thusly after Augustus Edward Hough Love, a Professor for Natural Philosophy at Oxford University who first described the movement of the waves named after him. This happens because although they move slower than body waves, their particle movement is much more pronounced (see below). In the case of Rayleigh waves, the motion is of a rolling nature, similar to an ocean surface wave. As opposed to body waves (S and P waves), they propagate on the surface and carry the vast majority of the energy felt on the surface - in other words, these are what you feel when you experience an earthquake. Surface waves (Rayleigh and Love) do by far the most damage. They also rarely do any significant damage. They’re also body waves but they only propagate through a solid medium. These are shear waves, which arrive after the P-waves.

They propagate longitudinally on the propagation direction (think of an accordion) and are harmless in terms of earthquake damage.

Primary waves (P-waves). These are the “first” body waves - the ones that travel the fastest and through any type of medium (solid, liquid, gas).

The main types of seismic waves are the following: Seismologists like to split seismic waves into several categories, but the main types of seismic waves come in two categories - body waves (which move throughout entire bodies, such as the Earth), and surface waves )(which travel only on different surfaces, not through the whole body). This requires very particular conditions to happen, but if it does happen, it creates a type of “anti-crack” and can generate massive, deep earthquakes. Their chemistry remains the same, but their volume and density change dramatically if an equilibrium is reached. Another cause of some very deep earthquakes is the so-called mineral phase change: atoms in minerals such as olivine can change their positions to become more tightly packed. Man-made explosions (for instance, atomic testing) can also produce earthquake-type features which produce seismic waves and can be detected - this is what allows remote monitoring of nuclear explosions.įor some earthquakes, the cause remains poorly understood, particularly in the case of intraplate tectonics (inside tectonic plates, not on the edges). Volcanoes can also produce earthquakes, though they are generally less impactful than tectonic earthquakes. If you look on a world map of earthquakes (represented here), you can distinguish the tectonic plates This is why, if you overlay a global tectonic plate map and a global earthquake map, you’ll see an almost perfect overlap between tectonic edges and temblors. The movement produces more and more stress on the ground until something eventually breaks along what’s called a geological fault. The Earth’s crust (the outermost layer) is split into rigid plates, all of which are moving relative to each other. Earthquakes can happen for a variety of reasons, but by far the most common cause is tectonic. In the broadest sense, an earthquake is just what the name suggests - any shaking of the Earth’s interior.

4 Studying the Earth with seismic waves.