SSBW - IRIS DMC Tutorial 5: Surface Wave Seismograms and Speeds

Mike Brudzinski, Miami University-Oxford

Initial Publication Date: August 18, 2021

Summary

In this interactive tutorial built for a learning management system, students 1) generate and interpret IRIS web service requests for metadata, earthquake information, and seismogram data (event, station, dataselect), 2) use SAC to visualize and interpret seismic arrival times and frequency content, 3) estimate seismic wave speeds from arrival times and source-to-receiver distances, 4) consider the causes of variations in seismic wave speeds due to variations in earth structure.

Seismology | College Upper (15-16)

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Context

Audience

The IRIS Seismology Skill Building Workshop (SSBW), which is a free, online, open-access, large-enrollment, 12-week summer workshop for upper level undergraduates.

Skills and concepts that students must have mastered

This assignment builds on prior experience using a Linux command line environment, IRIS web service requests, the SAC (Seismic Analysis Code) software, and an understanding of seismic wave frequency content, and how to pick seismic wave arrival times.

How the activity is situated in the course

This is assignment number 18 of 35 in the Seismology Skill Building Workshop (SSBW).

Goals

Content/concepts goals for this activity

Proficiency with IRIS Web Services, finding appropriate seismic stations, surface waves, SAC, frequency content, dispersion, filtering.

Higher order thinking skills goals for this activity

Retrieving relevant information from digital sources to accomplish tasks, using correct programming syntax, evaluating and describing computing output in the context of science concepts.

Other skills goals for this activity

Description and Teaching Materials

Students will:
1. Use the event web service to identify the largest earthquake near the center of the contiguous US
2. Use the station web service to identify a seismic station near the east coast of the US and a station at similar distance in the western US
3. Use the dataselect web service to retrieve SAC format seismograms from these stations
4. Identify the source to receiver distances using SAC
5. Pick P wave arrival times and use them to calculate speeds in the east and west directions
6. Filter the seismograms and pick multiple surface wave arrival times to account for dispersion
7. Calculate surface wave speeds in the east and west directions and interpret what the differences indicate about earth structure
8. Estimate the frequency of surface wave arrivals and how frequency is related to speed

Show Student Learning Outcomes

Student Learning Outcomes (with corresponding Question #s that address them):

Retrieve relevant information about geography and Earth structure from internet research or help pages (Q1, 2, 4, 27).
Identify which IRIS web services should be used to access data, metadata, events (Q2).
Use the URL Builder to generate a web service request for specific metadata or earthquake information (event, station) (Q3, 9, 10, 12).
Interpret web service output tables for data or earthquake information (Q3, 6, 7, 8, 10, 12).
Create and navigate directories on a Linux system (Q4).
Use wget and unzip on Linux to make web service requests and unpack data (Q4, 15, 16, 17).
Discern which command to use to return information about or within a text file (Q4, 5).
Correctly identify or specify the network, station, channel, and location codes for a given recording. For channel, this involves frequency, gain, and orientation attributes (Q9).
Calculate longitude, latitude, or distance from earthquake-station separation (Q11, 12, 19, 20)
Calculate a properly formatted date and time for arrivals and data requests using an earthquake origin and/or travel time (Q13).
Use the URL Builder to generate a web service request to retrieve seismogram data (dataselect) (Q14).
Use SAC commands LISTHDR and CHNHDR to review and change seismogram metadata (Q18, 19, 20, 22, 23, 29, 30, 31, 32, 39, 40)
Use SAC command PPK and WH to discern, pick, and save arrival time information (Q22, 23, 29, 30, 31, 32, 39, 40).
Calculate average seismic wave speed from epicentral distance and travel time (Q24, 25, 33, 34, 35, 36)
Calculate a percentage difference (Q26, 37)
Interpret Earth structure based on seismic wave speeds and frequencies (Q27, 38, 41)
Discern which type of filter to use based on the seismic wave of interest (Q28, 29)
Use SAC commands RMEAN and LP to remove the mean and filter a seismogram (Q29)

GIFT format file for SSBW IRIS DMC Tutorial 5 -- educator-only file

Teaching Notes and Tips

This assignment was constructed in the Moodle learning management system, and has been exported in the GIFT format. More information about the syntax of this format can be found here: https://docs.moodle.org/en/GIFT_format

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Assessment

This assignment is automatically graded by the learning management system. The number of questions of each type used are:
8 multiple choice questions
1 multiple answer question
22 numeric questions (earthquake info, pick times, distance, velocity, and percent calculation, period measurement)
10 short answer (auto-graded) questions

References and Resources

During the Seismology Skill Building Workshop, students are provided with a virtual Linux machine that was tailored to include the software specifically needed to complete the assignments. This software is all freely available on the internet, but interested parties are encouraged to contact the instructor for access to this tailored virtual machine.

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