Magnitude / Intensity Comparison Jump to Navigation Magnitude / Intensity Comparison Magnitude and Intensity measure different characteristics of earthquakes. Magnitude measures the energy released at the source of the earthquake. Magnitude is determined from measurements on seismographs. Intensity measures the strength of shaking produced by the earthquake at a certain location. Intensity is determined from effects on people, human structures, and the natural environment. Magnitude / Intensity Comparison The following table gives intensities that are typically observed at locations near the epicenter of earthquakes of different magnitudes. Magnitude Abbreviated Modified Mercalli Intensity Scale I. Not felt except by a very few under especially favorable conditions. II. Felt only by a few persons at rest, especially on upper floors of buildings. III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated. IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. V. Felt by nearly everyone; many awakened.

Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop. VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight. VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent. XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly. XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air. From The Severity of an Earthquake. How Are Earthquake Magnitudes Measured? How Are Earthquake Magnitudes Measured?

The Richter Scale Figure 1 - Charles Richter studying a seismogram. There are a number of ways to measure the magnitude of an earthquake. The first widely-used method, the Richter scale, was developed by Charles F. Richter in 1934. It used a formula based on amplitude of the largest wave recorded on a specific type of seismometer and the distance between the earthquake and the seismometer. That scale was specific to California earthquakes; other scales, based on wave amplitudes and total earthquake duration, were developed for use in other situations and they were designed to be consistent with Richter’s scale. The Moment Magnitude Scale Unfortunately, many scales, such as the Richter scale, do not provide accurate estimates for large magnitude earthquakes. Today the moment magnitude scale, abbreviated MW, is preferred because it works over a wider range of earthquake sizes and is applicable globally. The moment magnitude scale is based on the total moment release of the earthquake. Moment is a product of the distance a fault moved and the force required to move it. It is derived from modeling recordings of the earthquake at multiple stations. Moment magnitude estimates are about the same as Richter magnitudes for small to large earthquakes.

But only the moment magnitude scale is capable of measuring M8 (read ‘magnitude 8’) and greater events accurately. Magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by a seismograph goes up ten times. Using this scale, a magnitude 5 earthquake would result in ten times the level of ground shaking as a magnitude 4 earthquake (and 32 times as much energy would be released). To give you an idea how these numbers can add up, think of it in terms of the energy released by explosives: a magnitude 1 seismic wave releases as much energy as blowing up 6 ounces of TNT. A magnitude 8 earthquake releases as much energy as detonating 6 million tons of TNT. Pretty impressive, huh? Fortunately, most of the earthquakes that occur each year are magnitude 2.5 or less, too small to be felt by most people. Magnitude scales can be used to desribe earthquakes so small that they are expressed in negative numbers.

The scale also has no upper limit, so it can describe earthquakes of unimaginable and (so far) unexperienced intensity, such as magnitude 10.0 and beyond. Here's a table describing the magnitudes of earthquakes, their effects, and the estimated number of those earthquakes that occur each year. The Mercalli Scale Figure 2 - Giuseppe Mercalli Another way to measure the strength of an earthquake is to use the Mercalli scale. Invented by Giuseppe Mercalli in 1902, this scale uses the observations of the people who experienced the earthquake to estimate its intensity. The Mercalli scale isn't considered as scientific as the Richter scale, though. Some witnesses of the earthquake might exaggerate just how bad things were during the earthquake and you may not find two witnesses who agree on what happened; everybody will say something different. The amount of damage caused by the earthquake may not accurately record how strong it was either. Some things that affect the amount of damage that occurs are: the building designs, the distance from the epicenter, and the type of surface material (rock or dirt) the buildings rest on.

Different building designs hold up differently in an earthquake and the further you are from the earthquake, the less damage you'll usually see. Whether a building is built on solid rock or sand makes a big difference in how much damage it takes. Solid rock usually shakes less than sand, so a building built on top of solid rock shouldn't be as damaged as it might if it was sitting on a sandy lot. Mercalli Scale vs Richter Scale - Difference and Comparison | Diffen Mercalli Scale vs. Richter Scale Diffen › Science › Geology › Weather 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 two scales have different applications and measurement techniques. The Mercalli scale is linear and the Richter scale is logarithmic. i.e. a magnitude 5 earthquake is ten times as intense as a magnitude 4 earthquake.

Comparison chart Mercalli Scale versus Richter Scale comparison chart Mercalli Scale The effects caused by earthquake The energy released by the earthquake Measuring Tool Quantified from observation of effect on earth’s surface, human, objects and man-made structures Base-10 logarithmic scale obtained by calculating logarithm of the amplitude of waves. Scale I (not felt) to XII (total destruction) From 2.0 to 10.0+ (never recorded). A 3.0 earthquake is 10 times stronger than a 2.0 earthquake. Consistency Varies depending on distance from epicenter Varies at different distances from the epicenter, but one value is given for the earthquake as a whole. Contents: Mercalli Scale vs Richter Scale Richter Scale reading of 2011 Tōhoku earthquake (it was followed by a tsunami ) Measurement The Mercalli Intensity Scale measures the intensity of an earthquake by observing its effect on people, the environment and the earth’s surface. The Richter Scale measures the energy released by an earthquake using a seismograph. A base-10 logarithmic scale is obtained by calculating the logarithm of the amplitude of waves recorded by the seismograph.

Comparing the Scales Richter Scale Magnitude (approx. comparison) I Noticed only by sensitive people 2 to 3 Resembles vibrations caused by heavy traffic 3 to 4 Felt by people walking; rocking of free standing objects 4 Trees sway, some damage from falling objects 5 to 6 General alarm, cracking of walls 6 Chimneys fall and some damage to building 6 to 7 Ground crack, houses begin to collapse, pipes break 7 Ground badly cracked, many buildings destroyed. Some landslides 7 to 8 Few buildings remain standing, bridges destroyed. 8 Total destruction; objects thrown in air, shaking and distortion of ground 8 or greater This video explains how earthquakes are measured using the Richter and Mercalli intensity scales. Applications and Use The Mercalli Intensity Scale is only useful for measuring earthquakes in inhabited areas and is not considered particularly scientific, as the experiences of witnesses may vary and the damage caused may not accurately reflect an earthquake’s strength. It is, however, used to compare the damage caused by earthquakes in different areas.

2010 Canterbury Earthquake The Richter scale is used to measure the magnitude of most modern earthquakes and allows scientists to accurately compare the strength of earthquakes at different times and locations. History The Mercalli Intensity Scale was developed by Italian volcanologist Giuseppe Mercalli in 1884 and expanded to include 12 degrees of intensity in 1902 by Adolfo Cancani. It was modified again by Harry O. Wood and Frank Neumann in 1931. It is known today as the Modified Mercalli Intensity Scale. The Richter Magnitude Scale was developed in 1935 by Charles Richter. It was initially created to study a particular area in California, using the Wood-Anderson torsion seismograph, to compare the size of different earthquakes in the region. He later adapted the scale so that it could measure the size of earthquakes around the globe. References Measuring the Size of an Earthquake Jump to Navigation Measuring the Size of an Earthquake Seismic waves are the vibrations from earthquakes that travel through the Earth; they are recorded on instruments called seismographs. Seismographs record a zig-zag trace that shows the varying amplitude of ground oscillations beneath the instrument.

Sensitive seismographs, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world. The time, locations, and magnitude of an earthquake can be determined from the data recorded by seismograph stations. The Richter Scale The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.

At first, the Richter Scale could be applied only to the records from instruments of identical manufacture. Now, instruments are carefully calibrated with respect to each other. Thus, magnitude can be computed from the record of any calibrated seismograph. Earthquakes with magnitude of about 2.0 or less are usually called microearthquakes; they are not commonly felt by people and are generally recorded only on local seismographs. Events with magnitudes of about 4.5 or greater - there are several thousand such shocks annually - are strong enough to be recorded by sensitive seismographs all over the world. Great earthquakes, such as the 1964 Good Friday earthquake in Alaska, have magnitudes of 8.0 or higher. On the average, one earthquake of such size occurs somewhere in the world each year. The Richter Scale is not commonly used anymore, as it has been replaced by another scale called the moment magnitude scale which is a more accurate measure of the earthquake size. Magnitude Modern seismographic systems precisely amplify and record ground motion (typically at periods of between 0.1 and 100 seconds) as a function of time.

This amplification and recording as a function of time is the source of instrumental amplitude and arrival-time data on near and distant earthquakes. Although similar seismographs have existed since the 1890's, it was only in the 1930's that Charles F. Richter, a California seismologist, introduced the concept of earthquake magnitude. His original definition held only for California earthquakes occurring within 600 km of a particular type of seismograph (the Woods-Anderson torsion instrument). His basic idea was quite simple: by knowing the distance from a seismograph to an earthquake and observing the maximum signal amplitude recorded on the seismograph, an empirical quantitative ranking of the earthquake's inherent size or strength could be made. Most California earthquakes occur within the top 16 km of the crust; to a first approximation, corrections for variations in earthquake focal depth were, therefore, unnecessary. Richter's original magnitude scale (ML) was then extended to observations of earthquakes of any distance and of focal depths ranging between 0 and 700 km.

Because earthquakes excite both body waves, which travel into and through the Earth, and surface waves, which are constrained to follow the natural wave guide of the Earth's uppermost layers, two magnitude scales evolved - the mb and MS scales. The standard body-wave magnitude formula is mb = log10(A/T) + Q(D,h) , where A is the amplitude of ground motion (in microns); T is the corresponding period (in seconds); and Q(D,h) is a correction factor that is a function of distance, D (degrees), between epicenter and station and focal depth, h (in kilometers), of the earthquake. The standard surface-wave formula is MS = log10 (A/T) + 1.66 log10 (D) + 3.30 . There are many variations of these formulas that take into account effects of specific geographic regions, so that the final computed magnitude is reasonably consistent with Richter's original definition of ML. Negative magnitude values are permissible. A rough idea of frequency of occurrence of large earthquakes is given by the following table: MS 6.0 - 6.4 210 This table is based on data for a recent 47 year period.

Perhaps the rates of earthquake occurrence are highly variable and some other 47 year period could give quite different results. The original mb scale utilized compressional body P-wave amplitudes with periods of 4-5 s, but recent observations are generally of 1 s-period P waves. The MS scale has consistently used Rayleigh surface waves in the period range from 18 to 22 s. When initially developed, these magnitude scales were considered to be equivalent; in other words, earthquakes of all sizes were thought to radiate fixed proportions of energy at different periods. But it turns out that larger earthquakes, which have larger rupture surfaces, systematically radiate more long-period energy. Thus, for very large earthquakes, body-wave magnitudes badly underestimate true earthquake size; the maximum body-wave magnitudes are about 6.5 - 6.8. In fact, the surface-wave magnitudes underestimate the size of very large earthquakes; the maximum observed values are about 8.3 - 8.7. Some investigators have suggested that the 100 s mantle Love waves (a type of surface wave) should be used to estimate magnitude of great earthquakes.

However, even this approach ignores the fact that damage to structure is often caused by energy at shorter periods. Thus, modern seismologists are increasingly turning to two separate parameters to describe the physical effects of an earthquake: seismic moment and radiated energy. Fault Geometry and Seismic Moment, MO The orientation of the fault, direction of fault movement, and size of an earthquake can be described by the fault geometry and seismic moment. These parameters are determined from waveform analysis of the seismograms produced by an earthquake. The differing shapes and directions of motion of the waveforms recorded at different distances and azimuths from the earthquake are used to determine the fault geometry, and the wave amplitudes are used to compute moment. The seismic moment is related to fundamental parameters of the faulting process. MO = µSd , where µ is the shear strength of the faulted rock, S is the area of the fault, and <d> is the average displacement on the fault. Because fault geometry and observer azimuth are a part of the computation, moment is a more consistent measure of earthquake size than is magnitude, and more importantly, moment does not have an intrinsic upper bound.

These factors have led to the definition of a new magnitude scale MW, based on seismic moment, where MW = 2/3 log10(MO) - 10.7 . The two largest reported moments are 2.5 X 1030 dyn·cm (dyne·centimeters) for the 1960 Chile earthquake (MS 8.5; MW 9.6) and 7.5 X 1029 dyn·cm for the 1964 Alaska earthquake (MS 8.3; MW 9.2). MS approaches its maximum value at a moment between 1028 and 1029 dyn·cm. Energy, E The amount of energy radiated by an earthquake is a measure of the potential for damage to man-made structures. Theoretically, its computation requires summing the energy flux over a broad suite of frequencies generated by an earthquake as it ruptures a fault. Because of instrumental limitations, most estimates of energy have historically relied on the empirical relationship developed by Beno Gutenberg and Charles Richter: log10E = 11.8 + 1.5MS where energy, E, is expressed in ergs.

The drawback of this method is that MS is computed from an bandwidth between approximately 18 to 22 s. It is now known that the energy radiated by an earthquake is concentrated over a different bandwidth and at higher frequencies. With the worldwide deployment of modern digitally recording seismograph with broad bandwidth response, computerized methods are now able to make accurate and explicit estimates of energy on a routine basis for all major earthquakes. A magnitude based on energy radiated by an earthquake, Me, can now be defined, Me = 2/3 log10E - 2.9. For every increase in magnitude by 1 unit, the associated seismic energy increases by about 32 times. Although Mw and Me are both magnitudes, they describe different physical properites of the earthquake. Mw, computed from low-frequency seismic data, is a measure of the area ruptured by an earthquake. Me, computed from high frequency seismic data, is a measure of seismic potential for damage. Consequently, Mw and Me often do not have the same numerical value. Intensity The increase in the degree of surface shaking (intensity) for each unit increase of magnitude of a shallow crustal earthquake is unknown.

Intensity is based on an earthquake's local accelerations and how long these persist. Intensity and magnitude thus both depend on many variables that include exactly how rock breaks and how energy travels from an earthquake to a receiver. These factors make it difficult for engineers and others who use earthquake intensity and magnitude data to evaluate the error bounds that may exist for their particular applications. An example of how local soil conditions can greatly influence local intensity is given by catastrophic damage in Mexico City from the 1985, MS 8.1 Mexico earthquake centered some 300 km away. Resonances of the soil-filled basin under parts of Mexico City amplified ground motions for periods of 2 seconds by a factor of 75 times. This shaking led to selective damage to buildings 15 - 25 stories high (same resonant period), resulting in losses to buildings of about $4.0 billion and at least 8,000 fatalities. The occurrence of an earthquake is a complex physical process. When an earthquake occurs, much of the available local stress is used to power the earthquake fracture growth to produce heat rather than to generate seismic waves.

Of an earthquake system's total energy, perhaps 10 percent to less that 1 percent is ultimately radiated as seismic energy. So the degree to which an earthquake lowers the Earth's available potential energy is only fractionally observed as radiated seismic energy. Determining the Depth of an Earthquake Earthquakes can occur anywhere between the Earth's surface and about 700 kilometers below the surface. For scientific purposes, this earthquake depth range of 0 - 700 km is divided into three zones: shallow, intermediate, and deep. Shallow earthquakes are between 0 and 70 km deep; intermediate earthquakes, 70 - 300 km deep; and deep earthquakes, 300 - 700 km deep. In general, the term "deep-focus earthquakes" is applied to earthquakes deeper than 70 km. All earthquakes deeper than 70 km are localized within great slabs of shallow lithosphere that are sinking into the Earth's mantle. The evidence for deep-focus earthquakes was discovered in 1922 by H.H. Turner of Oxford, England. Previously, all earthquakes were considered to have shallow focal depths.

The existence of deep-focus earthquakes was confirmed in 1931 from studies of the seismograms of several earthquakes, which in turn led to the construction of travel-time curves for intermediate and deep earthquakes. The most obvious indication on a seismogram that a large earthquake has a deep focus is the small amplitude, or height, of the recorded surface waves and the uncomplicated character of the P and S waves. Although the surface-wave pattern does generally indicate that an earthquake is either shallow or may have some depth, the most accurate method of determining the focal depth of an earthquake is to read a depth phase recorded on the seismogram. The most characteristic depth phase is pP. This is the P wave that is reflected from the surface of the Earth at a point relatively near the epicenter. At distant seismograph stations, the pP follows the P wave by a time interval that changes slowly with distance but rapidly with depth. This time interval, pP-P (pP minus P), is used to compute depth-of-focus tables.

Using the time difference of pP-P as read from the seismogram and the distance between the epicenter and the seismograph station, the depth of the earthquake can be determined from published travel-time curves or depth tables. Another seismic wave used to determine focal depth is the sP phase - an S wave reflected as a P wave from the Earth's surface at a point near the epicenter. This wave is recorded after the pP by about one-half of the pP-P time interval. The depth of an earthquake can be determined from the sP phase in the same manner as the pP phase by using the appropriate travel-time curves or depth tables for sP. If the pP and sP waves can be identified on the seismogram, an accurate focal depth can be determined. by William Spence, Stuart A. Sipkin, and George L. Choy Earthquakes and Volcanoes What is the Richter Scale? (with pictures) Hobbies What is the Richter Scale? Originally Written By: Michael Anissimov Revised By: G.

Wiesen Last Modified Date: 21 December 2016 Copyright Protected: 10 hilariously insightful foreign words The Richter scale, officially called the "Richter Magnitude Scale ," is a numerical value used to measure the power of earthquakes . It is a logarithmic scale based on the amplitude of waves recorded by a seismograph . This means that each whole number increase on the scale corresponds to an absolute increase by a factor of ten. Earthquakes measured at less than about 2.0 on the Richter scale are not very serious, and can barely even be measured, much less felt. An earthquake is usually considered much more serious, and is felt by most people, once it hits about 5.0. What the Numbers Mean Each number of the Richter scale is equal to a ten-fold increase in the magnitude of an earthquake. In other words, an earthquake measuring 6.0 on this scale has a magnitude ten times greater than a 5.0 quake. One whole number increase also indicates that about 31 times more energy was released during a quake. It is theoretically possible to have an earthquake of 10.0 or stronger, although this has never been recorded.

Such a quake would be classified as Massive, and cause devastation across a very wide area. Ad Magnitude vs. Damage It is important to distinguish between the magnitude of an earthquake and damage it causes. Although higher numbers usually indicate more damage — and such earthquakes are often described in terms of damage — the Richter scale cannot be used as a direct measurement of the destructive force of a quake. Many factors contribute to the amount of destruction and loss of life caused by an earthquake, including the population of the area, the type of building construction, the type of earthquake, and how deep the quake is. A 5.0 magnitude quake hitting a densely populated area with old or poorly constructed buildings, for example, is likely to do more damage than a 7.0 earthquake that occurs in a remote region with few people or structures. How Earthquakes Are Recorded Seismographs record the magnitude of an earthquake. These devices detect waves traveling through the earth and portray them as a series of lines that move up and down. Greater movement in the earth creates more extreme differences — or amplitude — in the lines that are recorded, creating a visual representation of the earthquake's waves. The Richter scale is based on measuring the intensity of this difference.

Higher numbers come from more extreme recorded patterns. In most cases, the seismograph isn't actually at the epicenter of an earthquake, however; it's often at least some distance away from the place where the quake actually occurs. Based on this distance, the machine is specially calibrated so that scientists can determine what the magnitude that it recorded would have been if it was actually located at the center of the quake. Limitations News releases about an earthquake can be confusing, as evaluating the actual magnitude often takes time. A preliminary value is usually released to provide an approximation for the power of the quake, but this does not always match the official value released after the data is fully analyzed. The Richter Magnitude Scale was developed in 1935, and it does have some additional limitations. Earthquakes with a magnitude above about 8.0 cannot be measured very accurately using this scale. While there is no upper limit, measurements are not as precise because of how they are made. The scale uses the size of the largest waves recorded by a seismograph, which ignores the smaller but steadier waves created by a quake. These smaller types of waves are more likely to cause structural damage during an earthquake since they tend to occur for longer periods of time.

Alternative Scales To accurately record Great earthquakes, a system called the moment magnitude scale (MMS) is often used. This scale is based on all waves created in an earthquake, including those that may take almost two minutes to reach the device that records them. Although most current earthquakes are actually measured by this scale, they are still frequently described as registering some number on the Richter scale. Another way to measure earthquakes is with the Mercalli Intensity scale, which measures how the surface of the earth reacts to the movement. This scale has 12 levels, written in Roman numerals, and was created to be easier for the average person to understand. For example, an earthquake that rates a III on the Mercalli scale feels similar to the vibrations caused when a large truck passes by, and can be felt, but is not always recognized as an earthquake. A quake rated a VI is clearly felt, moves furniture around, and can even knock some plaster from walls, but does not cause major damage. A IX causes considerable damage, and may cause buildings to partially collapse; a XII, the highest rating, indicates a quake that throws items into the air and causes major destruction.

Ad Magnitude/Intensity | Pacific Northwest Seismic Network Magnitude/Intensity Magnitude/Intensity Perhaps no seismic subject is as irksome to seismologists as discussions of earthquake size. There often seems to be no end of confusion, misunderstanding, and over-interpretation of what are really pretty crude metrics. And when news announcers mention the "Richter Scale" seismologists the world over begin gnashing their teeth. Magnitude A familiar analogy to help understand earthquake size metrics is to think about a light bulb. One measure of the strength of a light bulb is how much energy it uses. A 100-watt bulb is brighter than a 50-watt bulb, but not nearly as bright as a 250-watt bulb. The wattage of a bulb tells you about the strength of the light source. In the same way, earthquakes magnitude is an objective measurement of the energy radiated by an earthquake. However, earthquake magnitude has no physical units, nor a meaningful 0. This is because we can't easily measure the energy the way we can with an electric circuit, so seismologists commonly use a relative measure.

It is easier to choose a particular earthquake recorded at a particular distance as a "standard" earthquake, call it a magnitude 1. An earthquake that causes ground motion at a seismic station (when corrected for distance) 10 times larger than the reference earthquake is M2. An earthquake causing motion at that distance 10 times larger than an M2 is an M3, and so on. To achieve this ten fold increase in ground motion require about 32 to 33 times the energy. When referring to the power or energy released in an earthquake this 32 mutiplier is used. An earthquake that releases about 33 times less energy and causes motion 10 times smaller than an M1 is an M0--and magnitudes can even go negative. This Live Science animation will help you visualize the expodential magnitude scale in terms of energy released. Intensity Earthquake intensity measures how strongly the earthquake impacts a specific location. In the light bulb analogy, it is the brightness with which you perceive the light at a place in a room. Can you read a fine-print book by the lamp? Pick up a needle? Perform delicate surgery?

Depends on the wattage of the bulb, and how far you are from it, right? If you mapped out the brightness in terms of what you could accomplish at the light level in a room, you'd have an intensity map. Well, you can make a map of earthquake impacts using the Modified Mercalli Intensity Scale (MMI), which derived from an earlier ten-degree Rossi-Forel scale , later revised by Italian vulcanologist Giuseppe Mercalli in 1884 and 1906 to quantify (somewhat) the earthquake effects. Further refinements for more modern construction were published in 1931 by the American seismologists Harry Wood and Frank Neumann. Measurements of instensity using the Modified Mercalli scale, are composed of 12 increasing levels that range from imperceptible shaking to catastrophic destruction, usually designated by Roman numerals, which stresses their semi-quantitative nature.

Whereas an earthquake will have one magnitude (well, as noted below, there are likely to be several different estimates of the magntitude of an earthquake depending on the type of estimate etc.), for each individual earthquake there will be a range of intensities depending in part on the magnitude of the source, but also the location of the site at which the intensity was observed. More about Magnitudes - The 3 Approaches If you've had some time to think a bit about the Earthquake/Light bulb analogy you probably have come up with some questions, like: But some bulbs are blue and some white and some yellow, what gives with that? And, flourescent fixtures put out really different quality light than incandescents, and are brighter for the same wattage, eh? And, what about a flash bulb from my camera which is incredibly bright...but just for a fraction of second? And, if my room is filled with steam or smoke, is the intensity still the same? These are all good points; it turns out that similarly for earthquakes the complexities and variability of earthquake rupture processes and of seismic waves as they travel through Earth (and evolving seismometer design and sensitivities) there are different methods for measuring the magnitude of an earthquake.

These may return a slightly different number when used to estimate the energy released in an earthquake. In overview, there are three approaches to using seismograph recordings to quantify earthquake sizes, with numerous flavors of each. One approach is to use some measure of peak amplitudes recorded on seismograms. A second is to use the duration of shaking recorded. A third is to try to match the actual waveform wiggle-for-wiggle with a mathematical model (a "synthetic seismogram"), and report the size of the modeled earthquake. 1. Amplitude based Magnitudes (Local, Body Wave, Surface Wave) The oldest and most famous magnitude measurement method, the Local Magnitude (it used to be referred to as the Richter magnitude), was developed by Dr. Charles Richter and Beno Gutenberg of Cal Tech in 1935. Written as ML, it remains the go-to method for measuring small- to medium-sized earthquakes within 600 km from the recording seismograph. Richter used seismograms recorded on a particular instrument, the Wood-Anderson torsion seismograph. Today, we use more modern instruments and account for their response to mimic what the historical Wood-Anderson seismograph would have produced.

Richter's motivation for creating the local magnitude scale was to measure the ratio of small- to medium-sized earthquakes. It was never intended to measure large or distant earthquakes. All amplitude-based magnitudes rely on a base-10 logarithm of the peak amplitude measured by a seismograph. This is because there are many factors of 10 difference between the smallest and largest amplitudes of observed ground motions. An earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger and corresponds to an energy release of 31.6 times greater than one that measures 4.0. Body wave magnitude is a similar concept, but applied usually to teleseisms -- earthquake more than 3000 km from the recording station -- and good for deep and shallow earthquakes. Surface wave magnitudes measure the surface waves that are generated by large regional to teleseismic earthquakes, and that travel long distances without losing much energy from absorption. In general local magnitudes "saturate" (lose resolution) for earthquakes exceeding M5.8 or so, body waves stay on scale to somewhat larger magnitudes, while surface wave magnitudes saturates at about M8 or so.

This is in general because of the frequencies of the seismic waves that each use. The higher-frequency methods (local, duration) can't see the difference between larger earthquakes, while the low frequency measures (surface waves, moment magnitude) characterize the long-wavelength energy that radiate from a bigger rupture surface. 2. Duration Magnitudes (coda magnitude) Another estimate of magnitudes is particularly useful when recordings "clip" and you can't measure the peak amplitude. This is called the coda magnitude, or duration magnitude, and is derived from the observation that the ratio of peak amplitude to the duration of shaking from an earthquake are related. PNSN often calculates the size of PNW earthquakes using the durations averaged from a number of seismograms to obtain "Md" estimates. In the past a seismic analyst picked the duration on each seismogram by eye independently, which was somewhat subjective and variable, as the background noise varies greatly. The modern method, made possible by faster computers, is to model the decaying amplitude of the seismogram in order to automatically and objectively define a duration. 3.

Waveform Modeling (moment magnitude) Modern digital seismic instrumentation, modern seismic theory, and most of all modern high-speed computers have permitted us to be able to model seismograms wiggle-for-wiggle. To do this, we use a standard model of the Earth and of the source to generate synthetic seismograms, and the computer adjusts the location, size, and orientation of the rupture to match the observed waveforms. The magnitude that is derived from waveform modeling is called the Moment magnitude, and it is in some ways the most precise estimate of earthquake size--and the only one applicable to great earthquakes M>8. Of great interest is that since we can observe the deformation of the Earth from such big earthquake ruptures, we have an independent estimate of the energy they released, so that we can (finally!) relate the magnitude to the energy released during rupture. It is worthwhile to note that all of these approaches have been calibrated and defined with respect to each other such that they all agree, on average, in the ranges in which they overlap. So for general purposes an M8 is an M8 is an M8, regardless of the method that generated it.

But also it is interesting that Richter's orignal local magnitude was the one that all the other techniques generally matched up with (since it was first) so, in a sense, the "Richter Scale" that news reporters often cite (to the chagrin of us seismologists) is really a pretty apt homage. Magnitude and Energy Below is a representation, from the Geological Society of America, of earthquake magnitudes and the equivalent energy release. (For the life of us, we don't know why the geologists used pounds of explosive as a proxy for energy instead of a real physical unit of energy, such as Joules! But the figure makes the point, anyway.) Notice the relationship is not linear? The change in the amount energy released from one magnitude to the next is greater as the earthquake magnitude increases. For example, the difference in amount of energy released from a magnitude 5 to a magnitude 10 is not double, it is 30 million times as much! Need some further practice relating Earthquake Magnitude to Energy?

No problem, the USGS calculates the difference between a 5.8 and 8.7 earthquake and has a calculator where you can input your own numbers to see how much bigger an earthquake can get with different magnitudes. Magnitude Vs. Intensity The chart below claims to compare Richter Scale magnitudes with intensities in a very generalized way--as if a "Richter magnitude" was somehow measuring the same thing as a "Mercalli intensity". Now that you know the basics of earthquake Magnitudes and earthquake Intensities, you know that this chart makes no sense. If you see it or a similar representation, you can be assured the provider of the information is unencumbered by knowledge of the basics. One Final Word - a Plea for Understanding Now that you know how many different approaches there are to measuring an earthquake, and how it depends on the traces that you use, and instrument types that you have available and how far they are from the earthquake, and how many there are.... Perhaps you'll understand why our magnitude estimates change with time immediately after an earthquake as we try to be both as fast and as accurate as possible. And why different organizations will post somewhat different magnitudes for the same earthquake.

A rule of thumb, perhaps is that in the early minutes (or tens of minutes) after an earthquake up to a half a magnitude unit of difference between estimates will generally be shrugged off by seismologists as reasonable scatter. But differences larger than that usually mean that there was a fairly serious problem...like the entirely wrong technique was used, or critical data were omitted. Contact Us What does the Mercalli scale measure? | Reference.com What does the Mercalli scale measure? A: Quick Answer The Mercalli scale is a seismic scale used to measure the intensity of an earthquake. The measurement is based on observations and experiences, and it is currently measured on a scale of 12 degrees of intensity, indicated by Roman numerals I through XII. Full Answer The original Mercalli scale was formulated in the late 1800s and early 1900s as a 10-degree scale. It was later modified several times, and its current form is known as the Modified Mercalli scale. The lower end of the scale is based on reports from people regarding the intensity of the effects they experienced, and the data is collected to form maps of intensity. The upper levels are generally based on observations of destruction caused by an earthquake, such as structural damage.

The Mercalli scale differs from the Richter scale, which measures the magnitude of earthquakes. The San Andreas Fault - VIII. "Magnitude" and "Intensity" What Do Earthquake "Magnitude" and "Intensity" Mean? Magnitude is a measure of the size of an earthquake. The Richter Scale, named after Charles F. Richter of the California Institute of Technology, is the best known scale for the measuring of magnitude (M) of earthquakes. The scale is logarithmic; a recording of 7, for example, signifies a disturbance with ground motion 10 times as large as a recording of 6. The energy released by an earthquake of M 7, however, is approximately 30 times that released by an earthquake of M 6; an earthquake of M 8 releases 900 times (30x30) the energy of an earthquake of M 6. An earthquake of magnitude 2 is the smallest earthquake normally felt by humans. Earthquakes with a Richter value of 5 or higher are potentially damaging.

Some of the world's largest recorded earthquakes--on January 31, 1906, off the coast of Colombia and Ecuador, and on March 2, 1933, off the east coast of Honshu, Japan--had magnitudes of 8.9 on this scale, which is open ended. As the Richter scale does not adequately differentiate between the largest earthquakes, a new "moment magnitude" scale is being used by seismologists to provide a better measure. On the moment magnitude scale, the San Francisco earthquake is estimated at magnitude 7.7 compared to an estimated Richter magnitude of 8.3. Strainmeter in a San Francisco tunnel monitors the nearby San Andreas fault. Full size image - 36k. Intensity is a measure of the strength of shaking experienced in an earthquake. The Modified Mercalli Scale represents the local effect or damage caused by an earthquake; the "intensity" reported at different points generally decreases away from the earthquake epicenter. The intensity range, from I - XII, is expressed in Roman numerals. For example, an earthquake of intensity II barely would be felt by people favorably situated, while intensity X would produce heavy damage, especially to unreinforced masonry.

Local geologic conditions strongly influence the intensity of an earthquake. Commonly, sites on soft ground or alluvium have intensities 2 to 3 units higher than sites on bedrock. The Mercalli Scale measures an earthquakes intensity measures intensity Introduction The Mercalli scale is commonly used by scientists after large earthquakes. Did you know there can be more than one intensity of an earthquake but only one magnitude? Intensity map of Chilean earthquake, USGS Intensity scale The intensity scale by Mercalli was the first earthquake scale invented. It measures the effects of the earthquake on people and buildings in different areas. Observations by people People fill out reports on what happened to them during an earthquake. They are asked if they were awakened by the earthquake, if furniture moved, was there damage to chimneys or to walls in their home. Questions reflect criteria for intensity Each of these questions are part of the criteria used to determine the intensity of the earthquake at their location. Engineers also examine structural damage to buildings and other man made structures. They file their reports with the earthquake center. Creating an intensity map The earthquake center uses the information from these observers to create an intensity map.

The map has circles radiating out from the epicenter of the earthquake with Roman numerals showing the intensity of the earthquake in different areas. Modified Mercalli scale The modified Mercalli scale used for these maps divides the intensity of the earthquake into twelve groups. Roman numerals I to XII are used to show the affects of the earthquake. Officials use intensity maps City officials and insurance companies use the intensity map after an earthquake to assess the damage to a town or region. They also use these maps to determine future housing regulations in an area. Insurance companies use projections to determine earthquake insurance. Major factors that affect the intensity of an earthquake. The greater the magnitude, the greater the intensity near the epicenter. A single earthquake can produce a range of intensities from I to XII. The intensity decreases as the distance from the epicenter increases until there is no affect felt by the earthquake. Earthquakes can have a range of intensities but only one magnitude. More Earthquake Links Normal Fault Find out why miners often find valuable ore in sites where normal faults have occurred. Megathrust Earthquake Find out why megathrust earthquakes will occur off the coasts of Alaska, Washington, Oregon and California in the future.

Earthquake Zones Find out where and why earthquakes occur and why there are earthquake zones. Moment Magnitude Scale Find out why the moment magnitude scale is used to measure great earthquakes 1964 Alaska Earthquake The Great Alaskan Earthquake find out why Good Friday saved many people's lives! The Mercalli Scale Did you know there can be twelve different intensities of an earthquake but only one magnitude? Find out why! What Causes Earthquakes. Find out what causes earthquakes and other fascinating facts about when our planet shakes, rattles, and rolls. Kids Fun Science The links on our Home Page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more. Richter Scale - How Earthquakes Work | HowStuffWorks How Earthquakes Work Prev Next Whenever a major earthquake is in the news, you'll probably hear about its Richter scale rating. You might also hear about its Mercalli Scale rating, though this isn't discussed as often. These two ratings describe the power of the earthquake from two different perspectives. The most common standard of measurement for an earthquake is the Richter scale, developed in 1935 by Charles F. Richter of the California Institute of Technology.

The Richter scale is used to rate the magnitude of an earthquake -- the amount of energy it released. This is calculated using information gathered by a seismograph . Up Next Famous Volcanoes Quiz The Richter scale is logarithmic, meaning that whole-number jumps indicate a tenfold increase. In this case, the increase is in wave amplitude. That is, the wave amplitude in a level 6 earthquake is 10 times greater than in a level 5 earthquake, and the amplitude increases 100 times between a level 7 earthquake and a level 9 earthquake. The amount of energy released increases 31.7 times between whole number values. As we previously noted, most earthquakes are extremely small. A majority of quakes register less than 3 on the Richter scale; these tremors, called microquakes, aren't even felt by humans. Only a tiny portion -- 15 or so of the 1.4 million quakes that register above 2.0 -- register at 7 or above, which the threshold for a quake being considered major [source: USGS ]. The biggest quake in recorded history was the 9.5 quake that struck Chile in 1960.

It killed nearly 1,900 people and caused about $4 billion in damage in 2010 dollars [source: USGS ]. Generally, you won't see much damage from earthquakes that register below 4 on the Richter scale. Richter ratings only give you a rough idea of the actual impact of an earthquake, though. As we've seen, an earthquake's destructive power varies depending on the composition of the ground in an area and the design and placement of man-made structures. The extent of damage is rated on the Mercalli scale. Mercalli ratings, which are given as Roman numerals, are based on largely subjective interpretations. A low intensity earthquake, one in which only some people feel the vibration and there is no significant property damage, is rated as a II. The highest rating, a XII, is applied to earthquakes in which structures are destroyed, the ground is cracked and other natural disasters, such as landslides or tsunamis , are initiated. Richter scale ratings are determined soon after an earthquake, once scientists can compare the data from different seismograph stations.

Mercalli ratings, on the other hand, can't be determined until investigators have had time to talk to many eyewitnesses to find out what occurred during the earthquake. Once they have a good idea of the range of damage, they use the Mercalli criteria to decide on an appropriate rating. Liquefaction In some areas, severe earthquake damage is the result of liquefaction of soil. In the right conditions, the violent shaking from an earthquake will make loosely packed sediments and soil behave like a liquid. When a building or house is built on this type of sediment, liquefaction will cause the structure to collapse more easily. Highly developed areas built on loose ground material can suffer severe damage from even a relatively mild earthquake. Liquefaction can also cause severe mudslides.

Question: The Richter scale measures the intensity of what?
Answer: Earthquakes