Linking Earthquakes and Geologic Time by Paleoseismology
Summary
In teaching general education Earth Science lecture, to make connections between separate topics I have created a paleoseismology activity that requires students to apply principles of relative geologic time to the record of prehistoric earthquakes. This activity is derived from Kerry Sieh's investigation of the San Andreas earthquake record at Pallet Creek, northeast of Los Angeles, using the simplified cross-section published by Susan Hough in her book Earthshaking Science (2002).
This activity has students apply relative geologic time principles (superposition and cross-cutting relationships) to a sedimentary record that records earthquake events to work out their timing and spacing (even spacing or bunched).
Context
Audience
General Education Earth Science lecture course (mostly non-majors, but our majors also take it) in the section dealing with physical geology. It could be used in an introductory physical geology class or in a lab too.
Skills and concepts that students must have mastered
The concepts of relative geologic time (superposition, original horizontality, cross-cutting relationships, inclusions).
Basic concepts of faulting and earthquakes.
How the activity is situated in the course
Geologic Time is covered about two weeks before I start Earthquakes. This activity occurs toward the end of my coverage of earthquakes when I'm beginning my discussion of earthquake forecasting/frequency.
Goals
Content/concepts goals for this activity
Reinforce learning of Relative Geologic Time Principles and their application to a societally relevant example (earthquake history) in "shallow time".
Interpret Earthquake recurrence along San Andreas Fault.
Hands-on, Minds-on approach to Learning
Higher order thinking skills goals for this activity
Integration of concepts from separate areas of physical geology
Other skills goals for this activity
Description and Teaching Materials
Hough's figure from Earthshaking Science (2002) shows a set of vertical ruptures caused by earthquakes in the Pallet Creek valley and horizontal peat beds. Students are first asked to decide what tools or principles would help work out the sequence of events. Some students want to immediately interpret the answer, but I tell them if you don't have a method first, then you can't get a reasonable answer. After thinking on their own, as a group, they gradually coalesce around the idea that superposition shows the fill of sedimentary layers in the valley and their order. Then cross-cutting relationships shows how much fill had occurred when each rupture happened. The top of the rupture marks the land surface at the time of the earthquake as the rupture couldn't leave a record in the air. They then can work out the sequence of the ruptures. The peat beds have radiocarbon dates; these can be placed into the rupture sequence by superposition and the students can evaluate earthquake numerical age and whether the earthquakes are evenly spaced or bunched.
Paleoseismology student exercise (Acrobat (PDF) 1.3MB Dec20 24)
Instructor notes for Paleoseismology Exercise (Microsoft Word 2007 (.docx) 35kB Jan7 25)
Pallet Creek diagram.tif (TIFF 1.3MB Jan3 25)
Teaching Notes and Tips
Susan Hough (2002) simplified the original information developed by Kerry Sieh and colleagues. Some information used in the activity is derived from Sieh and LeVay (1999).
The activity has generally taken 35-40 minutes, although since Covid, it seems to take longer.
See Instructor Notes for further information.
Assessment
While students generally seem to work through the activity well, I have had trouble coming up with successful assessments for the subsequent exam. I have tried short answer questions and multiple choice questions with a tendency for greater emphasis on the process or method rather than the particular answer.
References and Resources
Hough, S.E., 2002, Earthshaking Science: Princeton University Press, Princeton, 238 p.
Sieh, K.E. and LeVay, S., 1999, The Earth in Turmoil: W.H. Freeman, New York, 324 p.