Earthquakes— Basic Terms and Principles - WebBookBlog


Sunday, June 7, 2020

Earthquakes— Basic Terms and Principles

Earthquakes— Basic Terms and Principles

Earthquakes— Basic Terms and Principles

Basic Terms

Major earthquakes dramatically show that the earth is a dynamic, altering system. Earthquakes, generally, symbolize a release of built-up stress within the lithosphere. They occur along faults, planar breaks in rock alongside which there's a displacement of 1 side relative to the other. Sometimes, the stress produces new faults or breaks; sometimes, it causes slipping along old, existing faults. Here are some basic terms and principles related to the earthquake.



When motion along faults occurs progressively and comparatively smoothly, it's referred to as creep. Creep is sometimes termed aseismic slip, which means fault displacement without significant earthquake activity—can be inconvenient but not often causes serious harm.

Earthquake/ Seismic Slip

When friction between rocks on either side of a fault prevents the rocks from slipping easily or when the rock under stress isn't already fractured, some elastic deformation will happen before failure. When the stress, at last, exceeds the rupturing strength of the rock (or the friction alongside a pre-existing fault), a sudden motion occurs to release the stress. This is an earthquake or seismic slip.


Elastic Rebound

With the sudden displacement and associated stress release, the rocks snap again elastically to their earlier dimensions; this behavior is known as elastic rebound.


Faults come in all sizes, from very small to thousands of kilometers long. Likewise, earthquakes come in all sizes, from tremors so small that even sensitive devices can barely detect them, to massive shocks that may level cities. (Certainly, the “aseismic” motion of creep is definitely characterized by many microearthquakes, so small that they're typically not felt at all.) The amount of damage related to an earthquake is partly a function of the quantity of gathered energy released because the earthquake happens.



The point on a fault at which the first motion or break happens during an earthquake is known as the earthquake’s focus or hypocenter.



The point on the earth’s surface straight above the focus is known as the epicenter. When news accounts inform where an earthquake occurred, they report the location of the epicenter.


The strike is the compass orientation of the line of intersection of the plane of interest with the earth’s surface. The dip of the fault is the angle the plane makes with the horizontal, a measure of the steepness of the slope of the plane.


Strike-Slip Fault

A strike-slip fault, then, is one along which the displacement is parallel to the strike (horizontal).


Transform Fault

A transform fault is a sort of strike-slip fault and reflects stresses acting horizontally. The San Andreas is a strike-slip fault.


Dip-Slip Fault

A dip-slip fault is one by which the displacement is vertical, up or down within the direction of dip. A dip-slip fault by which the block above the fault has moved down relative to the block beneath is known as a normal fault.

Rift valleys, whether along the seafloor spreading ridges or on continents, are generally bounded by steeply sloping normal faults, ensuing from the tensional stress of rifting. A dip-slip fault by which the block above has moved up relative to the block below the fault is a reverse fault and indicates compressional stress other than tension.

Thrust Faults

Convergent plate boundaries are sometimes characterized by thrust faults, that are simply reverse faults with relatively shallowly dipping fault planes.

All described above are general and basic terms and principles related to earthquakes.


Also Read: 5 Effects of Earthquakes

Earthquake Locations

The places of main earthquake epicenters are concentrated in linear belts. These belts correspond to plate boundaries. Not all earthquakes happen at plate boundaries, however, most do. These areas are where plates jostle, collide with, or slide past one another, where relative plate motion could build up very massive stresses, where main faults or breaks may exist already on which further movement may happen.


In this article, basic terms and principles related to earthquakes are discussed like a creep, seismic slip, elastic rebound, focus, faults, and many more. One should understand these terms to enhance his knowledge related to earthquakes.

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