What is Up with the Bizarre Richter Scale?

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called the Richter Scale but how does this scale actually work how do seismologists gauge the strength of one of the most complicated geological phenomena's known oh well grab your emergency case and take shelter onto the newest doorway as we dive into the fascinating science and history of measuring earthquakes now before we begin it is important to note that while the Richter Scale has become synonymous with earthquake measurement the scale proper is actually no longer used to have been replaced in 1979 by the more accurate and versatile moment magnitude scale however the moderate earthquake intensities two scales are roughly similar and to understand the current system it is necessary to understand the history and development of its famous predecessor the ride detection and measurement of earthquakes is a surprisingly ancient practice with the first modern seismometer being built in China in 132 CE by the great Han Dynasty mathematician and scientist Chang Heng this instrument consisted of a two meter tall egg-shaped bronze vessel around which were mounted eight sculpted dragons with hinged Jaws holding a small metal ball below these sat eight bronze frogs with open mouths inside the vessel hung a heavy metal pendulum which was linked to each of the dragon's Jaws when the size make waves from a distant earthquake pass through the instrument The Vessel moved while the pendulum stayed still via inertia this in turn caused the dragon facing the direction of the earthquake's epicenter to release its ball into the Frog's mouth the instrument proved remarkably effective as Chang hang later wrote on one occasion one of the Dragons let fall a ball from its mouth through no perceptible shock that could be felt all the scholars at the capital changan were astonished at this strange effect occurring without any evidence of an earthquake to cause it but several days later a messenger arrived bringing news of an earthquake in Long sea 400 miles away upon this everyone admitted the mysterious power of the instrument so while modern seismometers are more sensitive and include systems for accurately measuring and recording seismic waves they all fundamentally work on the same basic principle as Chang heng's pioneering design using a pendulum or a weight suspended on Springs as the detection element however such instruments would not be developed until the 1920s meaning early scales for classifying earthquakes were based on their physical effects AKA its intensity one of the earliest was The Rossi Boral scale developed by seismologists Michelle Stefano Conte de Rossi and Francois Alphonse forel in 1873 divided into 10 categories like the Beaufort scale for measuring wind speed The Rossi Pharrell scale was based on qualitative observations of common earthquake effects for example an intensity one and two earthquake was unnoticeable by most people and intensity five earthquake could shift furniture and ring church bells an intensity seven earthquake could crack walls and bring down chimneys while an intensely 10 earthquake was the most catastrophic of all capable of leveling entire cities and tearing open the ground this girl remained in use until 1902 when Italian volcanologist gisepe merchale developed his eponymous Macaulay scale which used 12 points instead of 10 though in density one still represented an earthquake undetectable by humans and intensity 12 a catastrophic disaster in 1931 macaulay's scale was refined by American seismologists Harry wood and Frank Newman to produce the modified Macaulay scale which is still used today by the way but such intensity scale were highly subjective and as truly reliable seismometers became available in the 1920s it soon became fear that the observed intensity of earthquakes on the ground did not match up neatly with its measured magnitude that is the actual energy released at its hypocenter indeed it was found that the intensity of an earthquake its effects on the surface depends as much on the depth of the hyper Center as the actual magnitude of the earthquake in other words a shallower less powerful earthquake can inflict more surface damage than a deeper more powerful one and in case you were wondering the epicenter of an earthquake is its origin point on the Earth's surface while the hypocenter lies below the epicenter where the tectonic plates actually Collide to correct this mismatch and standardize earthquake measurement in 1935 American seismologist Charles Francis Richter introduced his famous eponymous scale which he initially referred to Simply as the local magnitude scale or simply the magnitude scale the scale is based on the then standard Wood Anderson torsion seismograph and expressed earthquake intensities as the logarithm of the maximum amplitude or height of the error recorded seismic waves expressed in microns or micrometers this means that the Richter scale is not linear instead each whole number magnitude represents an earthquake 10 times more powerful than the previous number for example the magnitude 4 earthquake is a thousand times more powerful than a magnitude one meanwhile the total energy released by an earthquake increases 31.7 times between whole number magnitude values Richter's magnitudes were calibrated such that a magnitude 3 earthquake detected by a wood Anderson seismometer located 100 kilometers from the epicenter would produce a trace on the recording chart one millimeter tool as the measured intensity of seismic waves changes with distance Richter also created a table of Correction factors to account for the actual position of the seismograph and the effects of local geology in practice the magnitude of a particular earthquake was determined by averaging the readings of multiple seismographs each corrected for their respected distance from the epicenter while Richter's name has become synonymous with this method his was actually a refinement of a similar method developed by a Japanese seismologist in 1931 which originally developed his skill specifically for use in California where earthquakes tend to be moderate in magnitude and seismometers are never more than 600 kilometers from the epicenter because of this and they're relatively low sensitivity of early seismometers the weakest earthquakes registered as magnitude 1 and the strongest around magnitude 8. however as more and more seismographs were installed around the world seismologists discovered that the accuracy of the Richter Scale fell apart at greater magnitude and distances a magnitude's above 6.5 values calculated using Richter's method tend to Cluster or saturate near one another causing the total energy release to be underestimated furthermore as seismometers became ever more sensitive they became capable of detecting earthquakes at magnitude lower than one which given the logarithmic nature of the Richter Scale translated into negative magnitude values to address these shortcomings vector and his colleague Beno Gutenberg developed the body wave magnitude and surface wave magnitude scales the former measures the magnitude of the primary or p waves and the a secondary or S seismic waves that travel through the Earth's interior while the latter measures the so-called love and rally waves that travel along the Earth's surface as the love and rally waves of earthquakes above magnitude 4.5 can travel all the way around the world the surface wave magnitude scale has no distance restrictions and can be measured from anywhere on the Earth's surface but while these scales were a marked improvement over Richter's original local magnitude scale magnitude values still tended to saturate magnitudes above eight as so in 1979 Japanese seismologist uru kanamori and American seismologist Thomas C Hanks introduced an entirely new measurement system the moment magnitude scale instead of measuring the peak amplitude of seismic waves recorded on a seismometer the moment magnitude scale is instead based on an earthquake's seismic movement that is the total displacement or slip of the tectonic fault across its entire surface during an earthquake multiplied by the force needed moves at fault this method avoids the saturation problem allowing earthquakes above magnitude a to be accurately measured however the scale still expresses magnitudes logarithmically and at moderate value lines up almost exactly with the old Richter Scale thus even though all seismologists now use the moment magnitude scale to report earthquake magnitude using the term Richter Scale as news reporters sometimes do is still technically accurate in most cases but what do the numbers on the moment magnitude scale actually mean as the earth's tectonic plates are constantly in motion earthquakes are happening all the time somewhere in the world the vast majority of these Quakes however are minuscule and undetectable by humans millions of such microquakes occur every year registering at magnitudes between 1 and 1.9 going up the scale magnitude 5 5.9 earthquakes are considered moderate but being readily felt by humans capable of inflicting minor damage to buildings and other infrastructure around a thousand to 1500 of these earthquakes occur every year worldwide magnitude 7 to 7.9 earthquakes on the other hand are considered major and can inflict major damage to buildings across a radius of 250 kilometers from the epicenter around 10 to 20 such crates occur every year and finally at the other end of the scale are extreme earthquakes a magnitude 9 or higher since regular seismic monitoring began in the early 20th century only five earthquakes of this magnitude have ever been recorded [Music] foreign [Music]