Albuquerque Seismological Laboratory
Ideas for Activities Using Live Seismograms from the LISS Website
This document provides some general ideas for educational activities which can utilize the helicorder-style seismogram plots (heliplots) on the LISS website. Some of the activities are quite basic and can probably be adapted to primary or middle school levels, while the more advanced exercises may be appropriate for undergraduate university level courses.
Exercise 1: Earthquakes, the media, geography
When a large earthquake is observed in some part of the world:
- Assign groups to search the newspapers for the next few days for reports of the earthquake (one can access newspapers all over the world via the WWW).
- If news reports are/aren't found discuss:
- Why was (wasn't) an earthquake in that part of the world reported?
- Does the US have economic or political ties to that area?
- Do US news agencies cover all parts of the world with the same thoroughness and accuracy?
- Assign groups to search the WWW for reports about the earthquake.
- Discuss the following (use Atlases, web searches, etc. to find the answers):
- What kind of damage may have happened in that area?
- How densely is the area populated?
- What kind of construction is typical for that area (modern, stone huts, thatched roof huts, etc.). What is the relation of the types of construction to the local geography, climate, etc.? How likely is earthquake damage to that type of construction?
- Have other big quakes hit the same area before?
- Are earthquakes typical for this area?
- You may want to look at a map that shows thousands of earthquakes from a period of several years to understand where earthquakes occur and how this relates to plate tectonics.
Exercise 2: Energy, attenuation
All of the heliplots on the LISS website have a magnification of 3000. This means that the waves drawn on the paper are 3000 times larger than the actual waves which passed under the seismometer. The magnification is only true when working from the postscript version of the plots. However, a typical computer screen displays the heliplots at about the same size as the printed postscript version.
- Note that recordings at some stations (the ones closer to the earthquake) are larger than others.
- Can you tell where (roughly) a new earthquake is by the relative size of the traces at the different stations?
- You may want to measure the largest amplitude portion of each seismogram and post these measurements on a world map.
- You can print the heliplots on paper and post the heliplots themselves on a world map (perhaps with a string connecting the plot to the station location).
- Discuss the relationship between magnitude (the measure of an earthquake's size--not distance dependent) versus an earthquake's intensity (how much shaking a quake produced -- which depends on where you are relative to the quake).
- Why does an earthquake produce less shaking further away?
- What happens to the energy radiated by an earthquake?
Exercise 3: Earthquake location lab
- Select heliplots where the P and S phases are visible and the station is within 100 degrees of the epicenter (the P and S phases are separated by less than 700 s).
- Mark the P and S times and compute the time difference (in seconds). This will require:
- determining scale of plot, in seconds/mm (typically done by measuring the length in mm of a 10 minute (600 second) interval marked on the plot)
- measuring the P to S interval, in mm
- convert P to S interval from mm to seconds, using conversion derived in step "a"
- Consult an S-P table or graph to determine epicentral distance, based on the observed S-P time interval (one can also use a plot of travel time curves and measure the S-P interval).
- Determine scale of globe. Using a piece of string, measure a 90 degree epicentral distance on the globe (e.g. measure from the north pole to the equator) to obtain a conversion factor for degrees-of-epicentral distance per mm.
- "Triangulate" for the earthquake location. For each station analyzed:
- consult station location table, and mark station location on globe
- create a string-and-chalk compass so that a circle can be drawn around the station, where the radius of the circle corresponds to the observed earthquake-to-station distance for that station. Do this by tying a loop in the end of the string and hold a piece of chalk in the loop. Hold the end of the string at the station location and measure out the appropriate amount of string so that the chalk can be used to mark a circle on the globe's surface.
- Items for discussion after the earthquake location exercise:
- How well did the three (or more) arcs drawn around the station intersect? What caused the errors? Some possibilities: mis-identified the S phase; lack of precision in measuring P to S interval due to small size of plot; used an inappropriate S-P distance table (the table provided is only valid for shallow source depths).
- Why do seismologists use universal time?
- Why can't you simply draw the circles around the stations on a flat (paper) map? You might want to go to the globe and draw a circle around a station at either a far south or far north latitude. See what landmarks the circle intersects then try to draw the same circle on a flat map. This is also an excellent opportunity to demonstrate the distortion of area created by Mercator style projections. For example, on the globe draw two circles of the same size, one centered on Iceland, one centered on Ecuador. Now see how these circles will be distorted if they were transferred to a flat map (the circle around Iceland will have to be much larger than the one around Ecuador).
- How do seismologists tell P waves from S waves!?
- Some concepts covered in this exercise:
- conversion of units
- increasing time between P and S arrivals as a function of distance
- the definition of epicentral distance (this requires thinking about how a plane intersects a sphere)
- distortion of maps
Exercise 4: Frequency content of seismograms
Compare the standard 24-hour, low frequency, heliplot for station ANMO with the special 12 hour, high frequency, heliplot for ANMO (at this time we only provide a high-frequency plot for ANMO).
- Find a large teleseism on the low frequency ANMO heliplot.
- Can this same earthquake be seen on the high frequency heliplot?
- Why do the distant earthquakes contain less high frequency energy than nearby earthquakes?
- Find earthquakes on the high frequency ANMO heliplot.
- You may want to consult the "Examples" page to see what western USA earthquakes look like on the ANMO high frequency plot.
- Can this same earthquake be seen on the ANMO low frequency plot?
- Sometimes the high frequency ANMO heliplot is quiet for hours, then it looks "noisier" for hours. This pattern repeats regularly. Why? Can you see this pattern on the heliplots for other stations?
- In between earthquakes some stations record nearly flat seismograms while others have a continuous background vibration.
- What is the period of this vibration?
- Do the stations with the largest background "noise" levels have something in common? Are they all near oceans or cities, for example?
Exercise 5: Surface waves
Find the surface waves on several heliplots from a large, distant, earthquake. The surface waves arrive later in the seismogram and are usually the largest amplitude arrivals.
- When you find a large surface wave arrival can you see the period (the peak-to-peak distance) of the surface wave change between the first arriving part of the surface wave and the tail-end of the surface wave? Which part of the surface wave arrives first, the lower or higher frequencies?
- Do the surface waves from the same earthquake recorded at different stations look the same or different? Do the differences seem to be related to whether the surface waves travel across ocean basins or continents?
- You may want to use a string stretched across a globe from the earthquake location to the station location to find the path that a surface wave takes (compare this to a straight line drawn between the same earthquake and station on a flat map).