# How are magnitude and intensity different (yet related)?

## Description

In this activity, students explore the relationship between an earthquake's magnitude and intensity. Students calculate the energy released during a weight drop (magnitude) and use an accelerometer (iPhone, QCN, or other) to investigate what happens to this energy as the source is moved further and further from the sensor (intensity). Students next examine USGS ShakeMaps to explore other factors besides and event size and the distance form the source to the receiver that can effect the intensity (e.g. geologic structures etc).

60 minutes

### Objective

• Students will be able to explain the information expressed in a three-component seismogram... particularly directions of motion, peak absolute amplitude and accelerations.
• Students will be able to explain how the magnitude of an earthquake, like their weight drop, is tied to the physical properties of the fault, and b) that
• Students will be able to explain several factors that contribute to the intensity of shaking at a particular location

### 5E Phase:

Explore/Explain. Students should already have experience with earthuqakes.

### Materials (per group):

• Accelerometer and computer (or iPods, USB, or other)
• Meter stick
• Tape
• Chair or water bottle

## Instructional Sequence

Open - Ask, how hard does the ground shake during an earthquake?  Have students model their perception of ground shaking kinesthetically with their notebook or text book.

Prior Knowledge - How could we test to see how accurate the students' modeling is?  Introduce sensors and three-component data to students.  Have volunteers model their shaking again and record  the acceleration of their modeling.

Explore/Explain - Compare student generated values to the actual values from the shake table example and from the Kobe earthquake (examples included in powerpoint).  Ask if the ground would shake like this everywhere during an earthquake?  How could we test this?  Preform weight drop experiment details in student handout and have student graph their results.

Reflect - Reflection on the results of the student experiment as a class...

• How much energy was released when you jumped or dropped the water bottle?
• Does this energy change depending on where you drop it horizontally?
• How would graph look different if we increased the mass, the height or both?
• What did you notice changing as you moved the drop location? (Energy transported by a wave is directly proportional to the square of the amplitude of the wave.)
• Where did the energy go? (Attenuation)
• Show record section (collection of seismograms from one event distributed by distance) from recent event noting different amplitudes yet same magnitude.

Apply - Examine a ShakeMap for an event (e.g. page 5 of student handout). Ask why, if distance is a factor that affects intensity,  isn’t the shaking around an area consistent and spherical?

Have students drop a mass from the same height above two different surfaces (e.g. floor and table) with the same distance between source and sensor. How do the records compare?  How might an understanding of this effect in the real world be valuable?