Trans-California Seismic Refraction Profile Analysis

Magali Billen
U. C. Davis, Department of Geology
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Homework assignment focused on identifying seismic arrivals and determining layer thickness and velocity using real-world data from a published article.

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Junior/senior level,elective course in the theory and analysis of geophysical field methods.
Designed for a geophysics course.

Skills and concepts that students must have mastered

Students need to have been introduced to travel-time diagrams, including the form of travel-time curves for reflected, refracted and direct waves. Although the students are encouraged to use MATLAB for the plotting and analysis, the assignment can be done on graph paper.

How the activity is situated in the course

One in a series of homework assignments on seismic reflection and refraction methods.


Content/concepts goals for this activity

Interpreting seismic travel-time data for crustal-scale velocity and layer structure. Recognizing the relationship between parameters in the travel-time diagram and in the subsurface structure.

Higher order thinking skills goals for this activity

Synthesis of understanding of different travel-time relationships.
Interpretation of results in terms of earth structure.

Other skills goals for this activity

Application of previously derived equations to real data. It is expected that students will have to seek out the information needed to answer the interpretive question on the web or in books from lower division geology courses.

Description of the activity/assignment

Homework assignment asks the students to analyze data from a refraction profile across California. The data is presented in a table together with the abstract and map figure scanned from a 1970s article in which the data was published and analyzed. The assignment requires the student to plot the data, determine line-fits to the three arrivals, identify the arrivals as the direct, reflected or refracted arrival and then to determine the layer velocities. They are asked to sketch a cross section of the profile with the layer properties and to illustrate representative travel time paths. In addition, they are asked to consider the velocities and layer thickness and determine what boundary in the continental crust the refracted waves come from. Finally they are asked to compare their results with the results presented in the abstract for the journal article and discuss any differences/similarities.

Determining whether students have met the goals

Students have met the goals of the assignment if they correctly identify the arrivals, determine the layer velocities and the layer thickness. For the interpretation questions, the students need to demonstrate that they understand which ray paths in the surface related to which parts of the travel-time curve and they need to explain why they have made the conclusions based on the results of their analysis.

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Supporting references/URLs

The data set included in the homework assignment is from the article published in:

Cardier D. S., A. Qamar, and T. V. McEvilly, Trans-California Seismic Profile-Pahute Mesa to San Francisco Bay, Bulletin of the Seismological Society of America, v. 60, no. 6, pp 1829-1846, 1970.