Trans-California Seismic Profile Analysis

Magali Billen

U. C. Davis, Department of Geology

Upper division, elective course in the theory and analysis of exploration geophysics methods.
Designed for a geophysics course

Students need to have been introduced to travel-time diagrams, the the travel-time curves from 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.

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

Interpreting seismic travel-time data for crustal-scale velocity and layer structure.

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

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.

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 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. The final question asks the student to consider the velocities and layer thickness and determine what boundary in the continental crust the refracted waves come from.

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 question, the response needs to explain why they have made the conclusions based on the results of their analysis.

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.