The main aim of Part B of this mid-term exercise is to answer a series of questions based on compilation of data that enable evaluation of the following hypothesis, posed as a question:
- Do all earthquakes on mid-ocean ridges and associated transform faults occur at shallow depth?
This page also provides links to the resources, previously utilized in Module 5 and in Phase I Group Activities, that help accomplish the task.
United States Geological Survey (USGS) (Links to an external site.) hosts a website with an interactive map that provides access to earthquake data. Its display is governed by menu icons that display a map of earthquakes, supplemented by a table of data that provides details of their magnitude, general location, timing, latitude, longitude, and depth. There is also a settings menu to choose the range of timing (past 7 days or 30 days) and magnitude (2.5+ or 4.5+), and navigation tools at the top of the map to select the region of interest and zoom in/zoom out.
This first series of questions requires you to identify earthquakes associated with specific features of the ocean floor, namely mid-ocean ridges and deep sea trenches associated with continental margins and island chains. It is recommended that you set parameters on the United States Geological Survey (USGS) (Links to an external site.) website to choose the settings that display earthquakes of magnitude M 2.5+ over the past 30 days rather than the default setting of the past 24 hours.
The default setting show plate boundaries as red lines and selecting terrain (rather than grayscale) under map layers in the settings sets a base map that shows major bathymetric features, which may be helpful in identifying earthquakes associated with mid-ocean ridges. Alternatively, the map of topographic features of the ocean floor used in the Ocean Bathymetry exercise can be found at the Satellite Geodesy operated by Scripps Institution of Oceanography (TopoMaps (Links to an external site.)).
Question 1: Identify five or more earthquakes that occurred on mid-ocean ridges or associated transform faults, including at least one example from each of the three major ocean basins, as follows:
- Earthquakes on the Mid-Atlantic Ridge and/or associated transform faults (i.e. within the Atlantic Ocean).
- Earthquakes on the East Pacific Rise, West Chile Rise, or Pacific-Antarctic Ridge and/or associated transform faults (i.e. within the Pacific Ocean)
- Earthquakes on the Southwest Indian Ridge, the Southeast Indian Ridge or the Mid-Indian Ridge and/or associated transform faults (i.e. within the Indian Ocean)
Provide details (magnitudes, locations, times, latitude/longitude, and depths) for all of the earthquakes you select.
A strong answer will choose a least five earthquakes that occurred on mid-ocean ridges or associated transform faults and report their details, specifically noting their depth.
Question 2: Summarize the depth characteristics of the earthquakes you identified associated with mid-ocean ridges and/or associated transform faults in the three different ocean basins (Atlantic, Pacific and Indian). Do the earthquake data for mid-ocean ridges and associated transform faults support or refute the hypothesis that all earthquakes in these tectonic settings occur at shallow depths?
A strong answer will describe the depth range of these earthquakes representative of mid-ocean ridges and associated transform faults in the three ocean basins and assess whether they are consistent with the hypothesis.
Question 3: Bonus Question (5 pt)
What aspects of the tectonic processes occurring at mid-ocean ridges provide a foundation for the hypothesis that all earthquakes in these settings should be shallow?
A strong answer will briefly describe why the tectonic processes at mid-ocean ridges are only likely to generate shallow earthquakes.