Spectral Seismology Module
- Develop the vocabulary needed to describe a seismic signal in both the time and frequency domain.
- Use spectral information to formulate an analysis plan.
- Demonstrate the ability to identify body and surface waves on seismic record.
- Demonstrate the ability to differentiate between seismic and acoustic signals.
Context for Use
This entire module can be completed in one 3-hour lab period or three 50-minute lecture periods for introductory or intermediate level students. Activities A and B could be completed with upper level students in one 50-60 minute lecture period plus a homework assignment.
This module has been used in a special topics course focused on time series analysis at the University of Washington and tested with introductory Geology Students at Queens College - CUNY. We anticipate the module could be used in a variety of courses as either a stand-alone lesson on seismology and waveform analysis or as a qualitative introduction in a course that teaches this material from a quantitative standpoint. Module materials can be tailored to increase or decrease the background information depending on students' quantitative skills.
Description and Teaching Materials
Quick overview of the activities in this module
See the teaching materials files, provided below, for a step-by-step description for carrying out this module. A student handout, describing Activities A, B, and C, and instructor answer key are also provided.
- Activity A: Students are introduced to wave propagation, waveforms, earthquakes, seismometers, seismic waves and seismograms.
- Activity B: Students explore the constructive nature of seismic waves, are introduced to the Fast Fourier Transform (FFT), and filters.
- Activity C: The spectrogram.
Workflow of this module:
- Give students their handout when they arrive to class.
- Instructor gives brief PowerPoint presentation on wave propagation, describing waveforms, earthquakes, seismometers, seismic waves, and seismograms. The PowerPoint can be presented prior to the activity or you can present a few slides at a time as your students work through the activity.
- After the presentation, the students divide into teams, open Seismic Canvas and start working with Earthquake data (Activity A).
- Students then construct synthetic waveforms and then use their knowledge to analyze seismic data (Activity B). This can be assigned as homework.
- Students use the FFT and the spectrogram to explore the characteristics of an unfamiliar acoustic signal (Activity C).
Teaching Notes and Tips
In Activity A, students respond to "catalyst questions" to demonstrate the ability to correctly use the terms frequency, amplitude, and period, formulate qualitative descriptions and sketches of high and low frequency signals they observe on a hand held seismometer, examine a pre-computed seismogram and answer questions using key terminology, and access the IRIS data base and describe recent earthquakes using key terminology.
In Activity B, students build a synthetic waveform using a web tool and see how individual frequency components in the time domain can be plotted in the frequency domain, add additional frequency components to their waveform and see how this is expressed in the frequency domain, and import seismic data and apply filters to wave forms.The act of constructing a waveform of increasing complexity builds the conception of waveform data as the sum of discreet frequency components. In addition, figure captions require students to qualitatively describe the waveforms they created.
In Activity C, students import seismic data from the IRIS database, plot it in the time domain, and preform a Fast Fourier Transform (FFT) using seismic canvas. The FFT is used to make comparisons of frequency content between the different parts of the seismic arrival. Students also create spectrograms and make comparisons to data. Figure captions require the student to describe the relationship between data plotted in the time domain, as an FFT and as a spectrogram.
Notes, tips, and an answer key are provided in the following files:
- Instructor's PowerPoint (PowerPoint 2007 (.pptx) 32.3MB May24 17)
References and Resources
Learn more about Seismic Canvas, from IRIS.