The earthquakes are the signals that our planet lives, that is in constant change and we are only a small part of its history. Join us as we explain it’s different movements here, changes are, You might learn a thing or two.
The tectonic plates emit shock waves that may be potent enough to alter the surface of the Earth, thrusting up cliffs and opening fissures in the ground and cause great damage collapse of buildings and other structures, also landslides, snow avalanches, tsunamis and volcanic eruptions.
While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us (USGS).
The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
Seismic wavesAre the waves of energy caused by the abrupt breaking of rock within the earth or an explosion. They are the energy that travels through the earth. There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves. Body waves can travel through the earth’s internal layers, but surface waves can only move along the surface of the planet like ripples on water.
Traveling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. These waves are of a higher frequency than surface waves.
The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave, and, consequently, the first to ‘arrive’ at a seismic station. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. Sometimes animals can hear the P waves of an earthquake. Dogs, for instance, commonly begin barking hysterically just before an earthquake ‘hits’ (or more specifically, before the surface waves arrive). Usually people can only feel the bump and rattle of these waves.
P waves are also known as compressional waves, particles move in the same direction that the the wave is moving in, which is the direction that the energy is traveling in, and is sometimes called the ‘direction of wave propagation.
The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium.
SURFACE WAVESTravelling only through the crust, surface waves are of a lower frequency than body waves, Though they arrive after body waves, it is surface waves that are almost enitrely responsible for the damage and destruction associated with earthquakes.
Love WavesThe first kind of surface wave is called a Love waves, It’s the fastest surface wave and moves the ground from side-to-side. Confined to the surface of the crust, Love waves produce entirely horizontal motion.
Rayleigh WaveThe other kind of surface wave is the Rayleigh wave. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.
Earthquake intensity depends on some factors that affect the amplitude and duration of shaking produced by an earthquake (earthquake size, distance from fault, epicenter, hypocenter and regional geology, etc.). Seismic waves can cause damage to buildings. The level of damage done to a structure depends on the amplitude and duration of shaking. The amplitudes are largest close to large earthquakes and the duration generally increases with the size of the earthquake. Regional geology can affect the level and duration of shaking but more important are local site conditions. generally shaking in soft sediments is larger and longer than when compared to shaking experienced at a “hard rock” site.
The earthquakes are measured and classified according to their intensity and magnitude, while the Mercalli scale describes the intensity of an earthquake based on its observed effects, the Richter scale describes the earthquake’s magnitude by measuring the seismic waves that cause the earthquake.
The Mercalli scale is linear and the Richter scale is logarithmic. For example, a magnitude 8 earthquake is ten times as intense as a magnitude 7.
Another effect caused by earthquakes on the surface are known as Landslides and Liquefaction, that generated under the stresses of seismic waves and are an obvious hazard generating large landslides.
In some cases, when the surface is underlain by a saturated, sand rich layer of soil, prolonged shaking can cause the expulsion of fluid from the sand layer resulting in a phenomenon where loses strength and stiffness causing it to behave like a liquid.
Another of the most dangerous effects of an earthquake and most famous is a Tsunami. Tsunamis are giant waves that can reach up to 30 meters in height and cause floods when entering the continent. Tsunamis often result from sub-sea faulting of ocean floor sending seismic shocks through the water and creating large waves of low amplitude but of long period, moving at 300-500 kmh.
An earthquake in general is the release and propagation of the energy accumulated by tectonic plates for thousands of years, this energy is transmitted in different wavelengths that is what we perceive as an earthquake, when it occurs on land, its magnitude depends of the geology in depth that is the medium by which the energy is transmitted (sedimentary rock or crystalline Rock) or if it happens in the sea, the energy is transmitted in the form of waves that can generate great destruction.
Now when you feel an earthquake, you know that you are feeling the energy release that our earth has stored for thousands of years! And that we are shaken by different types of waves and at different times.