Teaching activity - The Modified Mercalli intensity scale
This resource for level 5 students illustrates how to interpret representations using an earthquake measuring scale.
About this resource
In this resource, students compare different versions of the same scale, providing an opportunity to strengthen their capability to make sense of representations in the context of science.
Teaching activity: The Modified Mercalli intensity scale
Mātauranga Māori
According to tradition, earthquakes are caused by the god Rūaumoko, son of Ranginui, the sky father, and Papatūānuku, the earth mother. See Te Ara: Earthquakes in Māori tradition for more.
Learning focus
Students compare at least two different versions of the modified Mercalli scale and discuss how and why this particular scale might have been constructed.
Learning activity
The Modified Mercalli intensity scale on the GeoNet page explains that the version used in New Zealand has been adapted for New Zealand conditions.
Numerous “international” versions of the scale can be found with a quick internet search, most of which also show minor variations from each other. Choose at least one of these to be compared with the New Zealand specific version.
After reading the information on GeoNet ask students:
- Is the scale qualitative (descriptive) or quantitative (based on numbers)? (This might cause some debate because the scale descriptors are subsequently converted to numbers, which is a typical feature of qualitative scales used by scientists when communicating with each other.)
- What does the scale describe and why will it vary from place to place? (It measures the felt intensity of the earthquake, and this varies according to distance from the epicentre, nature of the ground in an area, etc.)
Now get students to compare the GeoNet version with another version:
- Ask students to list at least three specific ways in which the GeoNet version has been modified by New Zealanders’ experiences of earthquakes. (For example, few international examples mention that animals can show alarm – why might that be?)
- Ask who might want to use this scale – and why is it important that there is one agreed version to use in New Zealand? (For example, an insurance company might want to base decisions about earthquake risks to buildings on historical effects in an area, or in similar areas. They can’t just make up a scale to suit their own purposes because other people have to be persuaded that their assessment is fair.)
Now discuss who might be allowed to make changes such as these, and why this scale would not work if anyone could write it how they wanted. (This is an opportunity to introduce the processes scientists use to build consensus around a model such as this scale. For example, journal articles and conferences where changes are proposed and discussed, the role of professional bodies in arbitrating disputes, etc.)
Scientists represent their ideas in a variety of ways, including models, graphs, charts, diagrams, written texts – and the measurement scales they use. Students need to understand that scientific scales have been deliberately constructed for specific purposes, and can be refined over time as they are used for these purposes. However, this does not mean that “anything goes” – understanding how critique and consensus building are used to impart authority to such scales is an important aspect of building science literacy. Understanding and using the literacy practices of science supports students to think in new ways.
What are we looking for?
Can students discuss the constructed nature of the Modified Mercalli intensity scale?
Do they appreciate that the scale descriptors have been developed over time by the consensus-building processes that also apply to science claims more generally?
If students are interested in the actual development of the Mercalli scale over time, a very short history of its development can be found on Wikipedia:
Other similar scales include the Beaufort scale for wind speed, which is briefly outlined on Weather Online:
The Science Learning Hub - Pokapū Akoranga Pūtaiao also has an activity in which students study damage descriptions from earthquakes and allocate a Modified Mercalli intensity (MMI) number:
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