Watch this short, 6 minute, video all about earthquakes and learn why they happen, when they happen and how. Understand how the richter scale is used, what it means and how it is measured to tell us about an earhquake’s magnitude.
Find out how many earthquakes happen around the world each year and how many of those cause damage or categorised as major earthquakes. Understand the richter scale in relation to how an earthquake is felt and its’ effects.
Learn the basics about plate tectonics, earth’s plate movements and how they create and cause plate boundaries and fault lines. Discover the various types of fault lines and how they are created. Convergent, divergent and strike slip faults.
Through engaging visuals and expert insights, you’ll gain a newfound appreciation for the precision and artistry of earthquake analysis, cause and effects as well as how modern buildings are designed to withstand these extreme forces of nature. Earthquake engineering.
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Earthquakes
Introduction
Hi everyone,
A lot of people have asked me about earthquakes, why they happen, the different types and how the magnitude and Richter scale is measured and what it means.
So, I have prepared this short, crash course if you’d like, video, to explain some of the basic facts about earthquakes.
So, let’s start from the basics.
Plate tectonics
Earth’s surface is divided into seven major plates or as they are called “plate tectonics”, plus a few minor ones. These plates move a few centimetres every year, constantly changing the shape of earth’s surface.
This map shows the major earth’s plates, their current movement direction and how they have transformed the shape of the earth as we know it today.
One can even move these 7 plates around, like a puzzle and see how each continent fits into the other, giving a strong indication of the past.
Their movement is made possible due to the semi-molten layers under the earth’s crust.
Two neighbouring plates can have a convergent movement, moving towards each other, or divergent, moving away from each other and transform movement when 2 plates slip together.
This movement causes powerful shock waves known as earthquakes, creating plate boundaries or fault lines.
Type of Plate Boundaries
Convergent
Convergent movement, depending on where it happens can create different types of fault lines.
In the ocean, one plate will move under the other, creating a subduction zone and a sea trench. At the top volcanic activity can create oceanic ridges and even new islands.
On the coast line, again the subduction zone will also create a trench and at the top a range of mountains or volcanoes can appear creating what is known as a ring of fire.
A Continental or inland convergent fault line can create a new mountain range.
Divergent
Divergent movement is when 2 plates move away from each other creating rift valleys inland, or new oceanic basins and new mid-ocean ridge mountains if there is volcanic activity.
Transform
Transform movement creates strike-slip fault lines when 2 plates move along each other horizontally in different directions, thus creating displacing shear zones.
Plate movement is not constant, and happens unexpectedly releasing extremely large amounts of pressure.
Earth’s plates are held together by friction, and the more time goes by, more pressure is built up. When the friction that holds them together cannot hold the pressure any longer, this results in violent movements, travelling in the form of waves away from the fault line. These waves are what we experience as earthquakes.
The RICHTER scale
For this, we had to find a way to easily measure and understand the force of such earthquakes. One of the ways to measure the magnitude or the force of an earthquake, is using the Richter Scale which was invented by Charles Richter back in 1934.
The Richter scale is more of an empirical scale, measured on seismographs or seismometers, and is calculated by measuring the time between the Primary and Secondary waves, which gives us the approximate distance, and then plotted onto a graph together with largest amplitude of the needle to give the scale of the earthquake.
Let’s have a look at this example. The time between primary and secondary waves was 24seconds, put this number on the left scale and this gives us the distance of the earthquake to the seismograph, in this example was approximately 200km. Then the largest amplitude of the needle was 23mm plotted on the right scale and the connecting line between the two scales results in the Magnitude of the quake in the Richter scale in the middle.
Statistics and facts
Now, let’s talk about some simple statistics. Hundreds of thousands of earthquakes happen every year around the world, but most of them are only recorded by seismographs and cannot be felt by people.
As a statistic, only about 20% of those can be felt by us and only 2% can cause damage. For example, in 2023, about 500,000 earthquakes were recorded of which only a 100 caused any type of damage.
The largest earthquake ever recorded was in 1960 in Chile of magnitude 9.5 in the Richter scale.
If we want to categorize earthquakes, an earthquake of magnitude under 3 is usually not felt, from 3 to 5 very rarely causes damage and over 7 is categorized as a major earthquake that can cause serious damage over large areas. All of course depend on various criteria such as type of soil conditions, building types and methods of construction, density of popylation and so on.
Conclusion
We experience earthquakes in the form of waves travelling from the source of the fault line towards us propagating through the earth’s crust.
Currently, there is no way to predict an earthquake, either when or where it will happen, its’ magnitude and the way its wave will reach us. So, basically engineers can only design a structure to withstand the force of nature, by using statistical data from previous earthquakes, using probability analysis models and assumptions to decide how each structure should be designed. These assumptions are made based on the importance and the expected life span of each structure, in order to calculate the applied forces. It would not be feasible or economical, to design all structures capable of withstanding the largest possible earthquake.
So, with this, I hope I have covered most of the basic facts about earthquakes.
