An earthquake?
Any sudden shaking of the ground brought on by seismic waves passing through the planet's rocks is referred to as an earthquake. When a kind of energy held inside the Earth's crust is abruptly released, typically when masses of rock rubbing up against one another unexpectedly crack and "slide," seismic waves are created. Geologic faults, which are confined areas where rock masses can move in relation to one another, are where earthquakes happen most frequently. The largest tectonic plates that make up the crust of the Earth are where the majority of the world's major fault lines are found.
TABLE OF CONTENTS
- 1906 San Francisco Earthquake
- Earthquake causes origins
- What is Seismology?
- What causes earthquakes
- Keypoints
- Mapping Earth's Inferior
- External links
Prior to the development of seismology at the beginning of the 20th century, nothing was known about earthquakes. Seismology, the scientific study of all elements of earthquakes, has provided solutions to some of the most perplexing questions, including why and how earthquakes occur.
1906 San Francisco Earthquake
Every year, approximately 50,000 earthquakes large enough to be felt without the use of instruments occur around the world. Or thereabouts 100 of them are large enough to cause significant damage if their centres are near areas of habitation. Large earthquakes happen about once a year on average. They have been responsible for millions of deaths and incalculable damage to property over centuries.
Earthquake causes origins
An earthquake occurs when two blocks of earth suddenly slip past each other. The fault or fault plane is the surface where they slip. The hypocenter is the location beneath the earth's surface where the earthquake begins, and the Epicentre is the location directly above it on the earth's surface. Foreshocks can occur during an earthquake. These are smaller earthquakes that occur in the same location as the larger one that follows. Scientists can't tell if an earthquake is a foreshock until the larger one occurs.
The mainshock is the largest, most powerful earthquake.
Aftershocks are always generated by mainshocks. These are smaller earthquakes that occur in the same location as the mainshock. Aftershocks can last for weeks, months, or even years after the mainshock, depending on the size of the mainshock.
What causes earthquakes and where do they happen?
cartoon of cutout wedge of earth
A simplified illustration of the earth's crust (brown), mantle (orange), and core (liquid in light grey, solid in dark grey).
The earth is divided into four major layers: the inner core, the outer core, the mantle, and the crust. The crust and upper mantle form a thin skin on the surface of our planet.
But this skin is not all in one piece; it is made up of many pieces, much like a puzzle covering the earth's surface. Not only that, but these puzzle pieces keep moving around, sliding past and bumping into one another. These puzzle pieces are known as tectonic plates, and the edges of the plates are known as plate boundaries. Many faults run along the plate boundaries, and the majority of earthquakes occur on these faults. Because the plates' edges are rough, they become stuck while the rest of the plate moves. Finally, when the plate has moved far enough, the edges of one of the faults unstick and an earthquake occurs.
Why does the earth shake when there is an Earthquakes
The energy that would normally cause the blocks to slide past each other is being stored while the fault edges are stuck together and the rest of the block is moving. All of the stored energy is released when the force of the moving blocks finally overcomes the friction of the fault's jagged edges and it unsticks. Like ripples on a pond, energy radiates outward from the fault in all directions in the form of seismic waves. The seismic waves move through the earth, and when they reach the earth's surface, they shake the ground and anything on it, including our houses and us.
How do earthquakes get recorded?
Seismograph cartoon illustration
The cartoon sketch of the seismograph shows how the instrument shakes with the earth below it, but the recording device remains stationary (instead of the other way around).
Earthquakes are recorded by instruments called seismographs. The recording they make is called a seismogram. The seismograph has a base that sets firmly in the ground, and a heavy weight that hangs free. When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not. Instead the spring or string that it is hanging from absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part is what is recorded.
The cartoon sketch of the seismograph shows how the instrument shakes with the earth below it, but the recording device remains stationary (instead of the other way around).
Earthquakes are recorded by instruments called seismographs. The recording they make is called a seismogram. The seismograph has a base that sets firmly in the ground, and a heavy weight that hangs free. When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not. Instead the spring or string that it is hanging from absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part is what is recorded.
What is Seismology?
The study of earthquakes and seismic waves that move through and around the Earth is known as seismology. Seismologists are scientists who research earthquakes and seismic waves.
Keypoints:
The P-wave is the first seismic wave that seismographs can
detect and travel through both liquid and solid rock.It is
the primary body wave.
Motion in S-waves
Secondary body waves of the S-wave that oscillate the
earthquake perpendicular to the wave's direction of travel.
They move 1.7 times more slowly than P waves. S waves
will not pass through liquids like water, molten rock, or the
outer core of the Earth because they cann't withstand shear
stresses.Vertical and horizontal lotions are created in the
ground surface by S waves.
Rayleigh-wave
The Rayleigh in motion Waves surface waves that love
elliptically and produce motion in both the vertical and
horizontal directions depending on the wave's
propagation direction.
Love-wave Motion
Surface waves known as "love-wave motion waves" move
perpendicular to the direction of wave propagation and
parallel to the Earth's surface.
Mapping Earth's interior
Seismic waves sample seismic velocities and boundaries in the Earth's interior. Seismic waves offer high-resolution noninvasive methods for studying the planet's interior because they frequently propagate effectively as they interact with its internal structure. The fact that the outer core of the earth is liquid was one of the earliest significant discoveries, suggested by Richard Dixon Oldham in 1906 and conclusively demonstrated by Harold Jeffrey's in 1926. The liquid core creates a "shadow" on the side of the planet opposite the earthquake where no direct S-waves are seen because S-waves cannot travel through liquids. P-waves also move through the outer core through the mantle much more slowly than they do. Seismologists have mapped the earth's mantle with a resolution of several hundred kilometres by using seismic tomography to process readings from numerous seismometers. This has made it possible for researchers to spot large-scale features like the expansive low-shear-velocity provinces close to the core-mantle boundary as well as convection cells.
External links[edit]
Wikimedia Commons has media related to Seismology.
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