How can the magnitude of an earthquake be measured

Magnitude measures the former, while intensity measures the latter. Magnitude describes the overall size of an earthquake as an event in the earth. Magnitude represents the total energy the earthquake radiates, and is calculated using information on how large an area moves, the distance that one side of the fault moves past the other, and the rigidity of the rock.

The international standard for measuring earthquake magnitude is called the moment magnitude scale and was formulated by Caltech seismologist Hiroo Kanamori with alumnus Thomas Hanks.

Caltech's Charles Richter conceptualized magnitude. He developed a method to numerically report the relative sizes of earthquakes before earthquake magnitude could be measured directly. He described the first magnitude scale, which came to be known as the Richter scale, in a paper published in Intensity describes how strong the shaking is at a given location.

In the United States and many other locations, intensity values are described with Roman numerals from I barely perceptible to X widespread destruction , using the Modified Mercalli Intensity scale. This definition of intensity requires a subjective judgment by an observer. For instance, if the shaking is strong enough to awaken most people, then the intensity will be assigned a level of V. Today, scientists also can measure instrumental intensity directly, calculating and assigning intensities based on recorded ground shaking in different locations.

While an earthquake has just one magnitude, its levels of intensity decrease with distance from the epicenter. The waves get smaller as they travel away from the fault. Think of a lightbulb: It has one wattage, but the brightness that energy produces decreases with distance as the light spreads out.

Magnitude: Earthquake size is a quantitative measure of the size of the earthquake at its source. The Richter Magnitude Scale measures the amount of seismic energy released by an earthquake. When an earthquake occurs, its magnitude can be given a single numerical value on the Richter Magnitude Scale. However the intensity is variable over the area affected by the earthquake, with high intensities near the epicentre and lower values further away. These are allocated a value depending on the effects of the shaking according to the Modified Mercalli Intensity Scale.

In an example, Magnitude can be likened to the power of radio or television waves sent out from a broadcasting station. Intensity is how well you receive the signal, which can depend on your distance from the energy source, the local conditions, and the pathway the signal has to take to reach you. Privacy Statement Disclaimer and Copyright. Staff Search. Earthquakes Earthquakes at a Plate Boundary. New Zealands Largest Fault.

The earliest seismoscope was invented by the Chinese philosopher Chang Heng in A. This was a large urn on the outside of which were eight dragon heads facing the eight principal directions of the compass. Below each dragon head was a toad with its mouth opened toward the dragon. When an earthquake occurred, one or more of the eight dragon What was the duration of the earthquake?

Why don't you report the duration of each earthquake? How does the duration affect the magnitude? The duration of an earthquake is related to its magnitude but not in a perfectly strict sense. There are two ways to think about the duration of an earthquake. The first is the length of time it takes for the fault to rupture and the second is the length of time shaking is felt at any given point e. How can an earthquake have a negative magnitude?

Magnitude calculations are based on a logarithmic scale, so a ten-fold drop in amplitude decreases the magnitude by 1. If an amplitude of 20 millimetres as measured on a seismic signal corresponds to a magnitude 2 earthquake, then: 10 times less 2 millimetres corresponds to a magnitude of 1; times less 0.

What does it mean that the earthquake occurred at a depth of 0 km? What is the geoid, and what does it have to do with earthquake depth? An earthquake cannot physically occur at a depth of 0 km or -1km above the surface of the earth.

In order for an earthquake to occur, two blocks of crust must slip past one another, and it is impossible for this to happen at or above the surface of the earth. So why do we report that the earthquake occurred at a depth of 0 km or event as a How do seismologists locate an earthquake? When an earthquake occurs, one of the first questions is "where was it?

Unfortunately, Earth is not transparent and we can't just see or photograph the earthquake disturbance like meteorologists can photograph clouds.

When an earthquake occurs, it What is the difference between earthquake magnitude and earthquake intensity? What is the Modified Mercalli Intensity Scale?

Magnitude scales , like the moment magnitude, measure the size of the earthquake at its source. An earthquake has one magnitude. The magnitude does not depend on where the measurement is made. Often, several slightly different magnitudes are reported for an earthquake. This happens because the relation between the seismic measurements and the Moment magnitude, Richter scale - what are the different magnitude scales, and why are there so many?

Earthquake size, as measured by the Richter Scale is a well known, but not well understood, concept. The idea of a logarithmic earthquake magnitude scale was first developed by Charles Richter in the 's for measuring the size of earthquakes occurring in southern California using relatively high-frequency data from nearby seismograph stations How do you determine the magnitude for an earthquake that occurred prior to the creation of the magnitude scale?

For earthquakes that occurred between about when modern seismographs came into use and when Charles Richter developed the magnitude scale, people went back to the old records and compared the seismograms from those days with similar records for later earthquakes. For earthquakes prior to about , magnitudes have been estimated by Filter Total Items: 6. Lamb, Rynn M.