Explore natural hazards in seismically active regions using geodetic, earthquake, and societal data.
Skills and concepts that students must have mastered
Other content useful knowledge:
What are the 4 basic classes of faults?
Do faults break all at once, or in many short segments?
How is stress stored between tectonic plates?
What happens when the crust is stretched?
How the activity is situated in the course
Content/concepts goals for this activity
- Identify and describe the types of data useful to investigate tectonic deformation and seismic hazard potential.
- Identify and describe the characteristics of tectonic deformation and seismic hazard potential for the student's chosen region.
- Use data collected from online data sources (including GPS data products from PBO) and elsewhere to quantify plate motion and deformation.
- Demonstrate her/his understanding of tectonic deformation and seismic potential by creating maps with relevant data and by developing oral/written report with results and discussion of findings.
Higher order thinking skills goals for this activity
- Formulating research question (hypothesis)
- Finding and analyzing data
- Interpreting maps, tables, and graphs
- Synthesizing ideas
Other skills goals for this activity
- Pattern and trends recognition
- Graphing and interpreting data
- Online mapping tools - ability to download data, interpret symbols on maps, create simple maps using Google Earth or hand-drawn maps
- Unit conversion
- Cause and effect: plate motion, deformation, earthquakes, faulting, etc impact the landscape and create distinct landforms
- Stability and change: sudden vs gradual change (plate motion vs fault movement from earthquakes)
- Construct and interpret scatter plots for bivariate measurement data to investigate patterns of association between two quantities
- Communication skills in writing and oral presentation
Description and Teaching Materials
- Current tectonic movement and deformation using GPS data
- Earthquake history (size, location, depth),
- Location and orientation of faults
- Land use and population density
- USGS shake potential maps
- (optional) Landforms (valleys, mountains, volcanoes, scarps, etc.)
- (optional) soil and sediment characteristics of the subsurface - basins vs bedrock
Students will work in teams of 2 to 4. Each team will research a different region so that the class can compare results of the different regions. Students choose a region that they are interested in, have vacationed, have wanted to visit, etc. Before finalizing their choice, students need to ensure that they have the different types of data for the region.
Introduction to the project
Students often learn the basics on how an earthquake is created, the different types of fault movement, and general information about tectonic plates and their movement. They might have learned that the land deforms and used high-precision GPS data to study plate motion and tectonic deformation. (see UNAVCO Educational Resources for classroom activities). During their study of earthquakes, they might have been exposed to the concept that earthquakes are more than a point but an area of movement along a fault - a length of the fault and a depth. Students often ask, if a portion of a fault slips, how does this impact the rest of the fault? Does this make another portion of the fault more susceptible to an earthquake?
This project provides students the opportunity to explore this question further. By investigating the relationship between tectonic deformation, plate motion, faults, earthquakes, and population data, students choose a seismically active region with a fault (or faults) to investigate the seismic risk of their region of study.
Defining a region
Students can choose segment of a known fault like the San Andreas, or they could look at a GPS/strain rate map and look for a sudden change of GPS velocities in a place that interests them, or they could look at an earthquake map, or the USGS fault map, or at a recent/historic earthquake in the news. Looking at the fault database can help with determining the region based on fault segments. Possible faults/fault zones/seismic zones include:
- One of the many faults adjacent to the San Andreas fault - San Simeon fault, Ortigalita, Calaveras, Hayward, Greenville, Santa Ynez, Sierra Madre, Garlock, San Jacinto etc.
- The Wasatch Front, UT - most slip occurs on the Wasatch fault, but the area is more complex than it appears at first glance, with relative rotation playing a significant role in observed GPS velocities.
- Central Nevada Seismic Belt - actually contains multiple faults, and slip on individual faults is not well known. A more holistic view could be explored.
- Owens Valley fault zone, eastern CA
- Cascadia or Aleutian subduction zone - because these subduction zones are offshore, there are no GPS instruments near the actual fault, so relative plate motion should be used to estimate convergence rates. Because they are such large-scale structures, spherical geometry becomes important and convergence rates are not constant along subduction zones. Also note that slab geometry, age, and topography all affect fault interactions in subduction zones.
- Seattle fault zone or Southern Whidbey Island fault zone - two smaller fault zones around Seattle
In California, regions make more sense if they are shaped the width of the state, and include about 50 km of the San Andreas fault. If students are interested in southern California, they should consider including a segment of the San Jacinto fault. Near San Francisco region, the Hayward fault should be included. In northern California, the triple junction would be included.
In Nevada/Utah/Colorado , to get the best tectonic deformation picture, students would choose a region that extends from east (western Colorado) to west (eastern California).
In Oregon and Washington , again, regions that are shaped to include a portion of the subduction zone and the width of the state. Note, there are volcanoes; GPS stations very near the volcano will show tectonic and volcanic movement. (Which could be a different but interesting exploration for a student)
Checking the region for data
Students perform online searches to determine basic seismicity (earthquake data) and deformation (using GPS) to choose a region that has earthquakes and shows some movement (as seen with the GPS vectors on a map) - and to check that there is data. Useful tools for this:
- UNAVCO GPS Velocities Maps (more info)
- IRIS Earthquake Browser
- The Global Strain Rate Map a quick way to see if the area is tectonically active - students would choose an areas where there is color on this map: (from http://gsrm.unavco.org/model/)
Making a forecast (not a prediction)
Based on the earthquake and GPS data for the region, students make a forecast as to overall hazard of the region and what areas within the region would have higher hazards than others.
Assembling the data
Students can use hand-drawn maps, Google Earth, and/or ESRI Arc-GIS online (its free up to 1000 points of data per data type) to pull the data together onto a single map. Encouraging students to use layers so that they can compare and contrast patterns between two different types of data at a time will allow them to build their story. To lessen cognitive load (to avoid overload), suggest to students to look at one then two types of data at a time, make observations, take notes of the patterns and trends, ask questions,interpret the data, develop potential conclusions, etc. Then add in the one set of data at a time.
Students should compile what data they can find:
- GPS velocities - Multiple map viewing tools show the velocity vectors at GPS stations. Stick with one GPS data source (either PBO or UNR).
- GPS time series csv files for stations within ~100 km of study area - these are useful to look at for earthquakes or anomalies in the data.
- Calculations and plots can be done in Excel
- Table/maps of historic earthquakes
- Table/map of prehistoric, large earthquakes (plotting magnitude vs. interval will not be linear as the student might expect)
- Fault database for fault characteristics, etc.
- Fault slip rates
- Shakemaps for given magnitudes
- (optional) DEM kmz images of scarps if available
- Maps to identify nearby towns, local geography
Some on-line data resources include:
Current tectonic movement and deformation using GPS data:
- UNAVCO GPS Velocities Maps (more info) : combined with UNAVCO PBO network maps (click on a circle then the link for more information about a GPS station)
- University of Nevada- Nevada Geodetic Laboratory (this site uses a different reference frame)
- Data Archive Interface - Look at PBO network, view time series plots, and download data as .csv:
- The Global Strain Rate Map from http://gsrm.unavco.org/model/)
Earthquake history (size, location, depth):
- IRIS Earthquake browser
- USGS - there are Google Earth files (kmz and Kmls) available from USGS
- (advanced) ANSS catalog
- USGS fault and fold database and fault slip rates
- USGS interactive fault map (more info)
- USGS shakeMaps
- Google Maps
- National Map Viewer - a great source of topographic and land-use data as well as air photos and satellite data.
- http://volcanoes.usgs.gov/hazards/ 'Volcanoes'
- Soil and sediment characteristics of the subsurface: Map Database for Surficial Materials
- Land use and population density
- Landforms (valleys, mountains, volcanoes, scarps, etc.)
- Seismic hazard maps
- Tsunami inundation maps:
Analyzing and interpreting the data
For your region of study, create a description of the seismic hazard potential then discuss the potential impact on the people who live in the region.
The student report should include the following:
- Describe the geologic setting of your study area:
- What kind of fault(s) are there?
- Describe the kind of data sources available. (Some faults are better instrumented than others.)
- Geodetic measurements of slip:
- Describe how fast are GPS stations moving on either side of the fault or fault zone.
- Describe the transitions in velocities across the fault: gradual, abrupt, etc.
- Identify GPS stations from a map view then create an x-y plot of velocity vs. cross-fault distance (distance from the fault; using the fault's location as zero). In some places like the Aleutians, students would have to look at relative plate velocities. (If a large region is used, spherical plate geometry becomes more important.)
- Or open the PBO GPS velocity file in a spreadsheet program; for for each GPS station, use the columns with dN/dt and dE/dt to calculate horizontal velocity (use either a graphical method or pythagorean equation to calculate the vector math), then create the x-y plot as described above.
- Historical earthquake magnitudes:
- By looking at paleoseismic history and historic earthquakes, estimate a range of earthquake magnitudes that could occur on the segment of the fault in your region. (Create a table with date, location, and magnitude)
- Slip rate:
- Describe the slip rate for the segment of the fault(s) within your region (mm/year). (from the USGS Quaternary Fault and Fold database - usually given as a range; values are generally less than GPS rates.)
- How does this slip rate compare to the GPS velocity differences across the fault?
- Definition of slip rate from USGS Earthquake glossary: The slip rate is how fast the two sides of a fault are slipping relative to one another, as determined from geodetic measurements, from offset man-made structures, or from offset geologic features whose age can be estimated. - however the reality is that the numbers for paleoseismic measurements don't quite equal geodetic. Propose some reasons why these might be different, remembering that an earthquake is a rupture area including the surface rupture length and depth.
- Maximum slip displacement (expected offset):
- Calculate the maximum displacement (MD) (slip that occurs during earthquakes, also called offset) for different Magnitudes that could be expected for the fault(s) in your region using the magnitude-rupture displacement scaling relations equation.
- Use this magnitude-rupture displacement scaling relations equation:
M = a + b*log10(MD)M=moment magnitudea=6.69±.04b=0.74±.07MD=maximum displacement
antilog[(M-a)/b] = MD
- And, if possible, find the offset directly from the fault database or other references.
- How does the USGS fault database for your fault segment compare to your calculation?
- Now that you know the expected offsets from an earthquake for different magnitudes, use the slip rate to calculate the time needed to load to that offset.
- What would the time be given an alternate slip rate?
- How often would an earthquake of a given magnitude occur given the slip rate you found for the fault? This can also be thought of as the Time needed to reload the fault (until another earthquake occurs), or the Earthquake frequency (recurrence rate)
- Reload time (years) = Maximum slip displacement / slip rate
- Using paleohistory and measured history of earthquakes : Describe the frequency rate of earthquakes at different magnitudes (1 earthquake per x years) (this might be shown as a table) for your region. How does the literature compare to your calculation?
- Describe what else would you need to to know to get a better estimate of earthquake return (recurrence) time/ seismic hazard/ risk:
- By identifying information you don't have helps determine the uncertainties involved.
- What other factors might affect the earthquake return time? (Possible discussion of fault interactions, pore fluid changes, and more exotic processes like glaciation, dynamic triggering, etc.)
- Another scaling relation is the Magnitude-Surface Rupture Length (since magnitude or offset aren't less often available than segment length).
- Calculate the Surface Rupture Length using the equation below.
- Using this surface rupture length, what would be the maximum depth possible of the fault? How does this compare to the fault database?
M = a + b*log10(SRL)a=5.08±.1b=1.16±.07SRL=surface rupture length (km)M=moment magnitude
- Based on earthquake frequency and magnitudes in your study area (scales of 10,000s, 1000s, or hundreds of years), describe the seismic hazard (low, medium, or high)?
- Provide a justification for your choice.
- What would be the societal effects of earthquakes in your study area; what kind of damage could be expected?
- Look at Shakemaps for your area and examples of similarly sized earthquakes in the news, fault location, geology (hard rock vs sediment), population, etc.
- Comment on the amount of potential damage and area affected to address the potential impact in the earthquake. Risk can vary greatly based on population density, building codes, and local geology, so any discussion will be open-ended.
- What's this all mean?
Teaching Notes and Tips
Locations for projects
- While place-based choices would be ideal to provide student connection to the investigation, some areas of the country are more seismically active than others.
- United States: Good data are available for the western United States, Alaska, and the basin and range region of Nevada into Utah.
- International locations are possible, but publicly available, open-source data sets like PBO GPS data or USGS fault data are not generally available. other GPS datasets are available. Try the University of Nevada- Nevada Geodetic Laboratory ). The student may find slip rate and paleoseismic history in published papers, but pulling together the required data requires some time and luck.
- Plate motion is close to 'zero', such as mid-continental United States:
- The PBO GPS dataset in NAM-08 (North American Reference frame) sets the motion of the mid-continent to close to zero so that the movement along the edges of the plate are more obvious. Swithcing to another reference frame won't necessarily help as the velocity differences between GPS stations most of the mid-continent are also close to zero.
- Have students choose a different location- Check the global strain rate map, GPS velocity maps, and earthquake browser to pick another area.
- International locations, they might be frustrated with
- No GPS data available within their study area: Try the University of Nevada- Nevada Geodetic Laboratory ; if there still isn't GPS data, then unfortunately they would need to either choose a different area with GPS data or not use GPS data at all.
Working in Teams
- In introductory undergraduate classes, students work in teams to work on this project. Team members help and collaborate with each other to map the data, analyze the patterns and visual distributions on the maps that they observe, and developing their conclusions about seismic potential.
- Depending on the class make up, assigning teams might be more success to that students with different strengths and challenges are paired together. Different group roles that the students assign to facilitate active participation and to draw on their strengths, may include: Scribe, Group Leader, Artist - Mapper, Data plotter, Discussion director, etc. Each student though should be part of the data analysis, interpretation, and results discussions.
- Students in more advanced (majors level) courses could work more independently, perhaps choosing regions with fault segments adjacent to each other, using group time to brainstorm, compare approaches, analyzes, and conclusions before submitting the project for grading (whether peer or instructor graded).
Common difficulties (with potential solutions) encountered by students during similar projects (From Linda Reinen's Watershed Analysis
Student teams give oral presentations to teach the class about their region.
After the student teams present, a post-presentation class discussion to compare and contrast the results from the different regions is an important synthesis step. Taking time to discuss the steps they went through to perform the research helps with meta-cognitive retention of the process.
You can also devise exam questions based on the project results. E.g., a brief discussion of regional variations in regional tectonics.
References and Resources
Next Generation Science Standards, Appendix G – Crosscutting Concepts (pdf)
Resources for students are embedded in the Description and Teaching Materials section.