Explaining Seismic Hazard Probabilities
Students will compose a memo to one of a group of audiences, explaining the Modified Mercalli Intensity scale, its relation to seismic hazards, and the concept of probability, in time and space, of earthquake occurence and seismic hazard. They will include a specific example in their memo and accompany the memo with appropriate maps and graphs.
Types of Seismic Hazard, their relationship to distance from fault and earthquake epicenter, topography and soil condition
Modified Mercalli Intensity Scale (and comparison to other measurements of earthquake strength)
Recurrence interval and probability, as applied to earthquakes and seismic hazards
Higher Order Thinking Skills:
Writing for different audiences
Explaining numbers (in this case, Modified Mercalli intensities, earthquake probabilities, peak ground acceleration, and seismic hazard)
Evaluating material written for different audiences
Reading and interpreting maps
Context for Use
Although a stand-alone exercise, it is also intended as an introduction to a larger project, in which students use census data and hazard maps in GIS to determine populations at risk.
This exercise is adaptable to a variety of settings. It can be started during a class period or lab session and completed as a homework assignment (either for individuals or groups). It could also be started and completed during a longer lab period.
In the course, this activity is part of a unit on earthquakes and seismic hazards, related to discussions of tectonic plate boundaries.
Before starting this activity, students will find it useful to have done some preliminary reading on ways of measuring earthquakes, on the Modified Mercalli Scale (in particular), and on the types of seismic hazards (fault rupture, shaking, liquefaction, landslides, etc.). Such information is readily available in environmental geology and natural hazards texts and on-line. Some suggestions are given below.
The most difficult concepts to understand (and therefore to explain in writing) are those centered around probability and recurrence. In a course where quantitative skills and concepts are introduced and mastered sequentially, you might want students already to be comfortable explaining data mapped on logarithmic scales (compared to linear scale), basic map reading (including distance measurements), and some basic statistics (measures of central tendency and variance).
The examples in this activity refer specifically to the Wasatch Front in Utah. This activity can be adapted using materials from other seismically active areas, such as New Madrid (Memphis, TN and St. Louis, MO), California (SF Bay Area, LA area and others), the Pacific Northwest (e.g. Seattle), and others, including areas overseas, such as Italy, Greece and New Aealand (as information permits). GIS-based maps and data may not be available for all overseas sites.
Description and Teaching Materials
The handouts include references to USGS and other sites with basic information. These sites are listed in the "Resources" section of this page, along with basic references on writing with numbers and natural hazards.
Teaching Notes and Tips
References and Resources
(last updated in 2004, accessed June 2, 2006)This is a short general interest USGS publication describing earthquake magnitude (Richter magnitude) and intensity (Modified Mercalli Intensity Scale).
This is a one-page general comparison of the Modified Mercalli Intensity (and damage) expected by earthquakes of different Richter magnitudes.
(from William Spence, Stuart A. Sipkin, and George L. Choy
Earthquakes and Volcanoes, Volume 21, Number 1, 1989; url accessed on June 2, 2006)
This is a more technical description of different kinds of magnitude calculations.