Subduction Zone Geometry in Three Dimensions:The Lesser Antilles
Subduction Zone Geometry in Three Dimensions:The Lesser Antilles
This activity allows you to use data from US government repositories to explore relationships between earthquakes, volcanoes and plates at convergent margins, that is, where a large piece of ocean floor descends below another portion of the Earth’s crust in the process of subduction.
Materials needed (all except the pencil are attached and/or available from PAESTA Classroom):
Dataset of earthquakes occurring over a period of 6-12 months in the Lesser Antilles
Dataset of volcano locations in the Lesser Antilles
Blank map (top view, or map view) of the Lesser Antilles with plotting grid included
Blank cross-section (vertical slice) through the Lesser Antilles with plotting grid included
Pencil with eraser
The accompanying file Kuriledata.xls contains a sample suite of earthquake data for students to use if you choose not to have them seek these values by themselves.
Part 1.Earthquake location data
The United States Geological Survey compiles a catalog of all earthquakes in the world of approximately magnitude >4.2 and all United States earthquakes of approximately magnitude >2. This catalog is openly available in a variety of searchable formats from this link: There are two possible ways to obtain a dataset of earthquake locations for this activity. You will either receive a data file prepared by your teacher or you will receive instructions from your teacher about how to download a dataset from the USGS website. In either case, you will need at least data from a time period of at least 6 months. This region uses two different plotting files of earthquakes so the full instructions are included with this document.
Using the data catalog, each studentmust plot the earthquake locations from their dataset onto two different maps. They first plot latitudes and longitudes on a traditional plan-view map (sheet 1 in the data file), and then plot longitude vs. depth on a cross-section-view map (sheet 2 in the data file). Be aware that the Lesser Antilles are in the western hemisphere, so the longitude values are negative.
Examine your maps and describethe relationship between earthquake locations and depth below the surface of the Earth. Formulate a claim about your observations that explains why the earthquakes are where they are. Think carefully about the evidence needed to support or refute your claim. When you have completed this section of the activity, you may move on to part 2.
Specific questions to answer:
- Look at your cross-sectional map. Describe the patterns that you see and the relationship between longitude and depth for the earthquake locations.
- How can we infer the location of the plate boundary from these data?
- How can we infer the type of plate boundary in this location?
- What is happening at this plate boundary to cause the earthquakes?
- Can you use these observations together with some scientific reasoning to support your claim about why the earthquakes occur in the pattern you described above?
- By looking at the earthquake locations, how can we infer the direction that each plate is moving at this boundary?
Part 2.Volcano location data
In this section, begin by adding the locations of known volcanoes on the two maps of earthquake locations. On Grid #1, plot the locations (longitude, latitude) of the following volcanoes using a different symbol than the one you used for the earthquakes. On Grid #2, plot the location of Pelee and Qualibouvolcanoes using latitude as the X coordinate and zero for depth. The information about the location of these volcanoes comes from the Smithsonian Institute’s Global Volcanism Program,
Volcanoes:
Nevis Peak: Latitude: 17.15 Longitude: -62.58
Soufriere Hills: Latitude: 16.72 Longitude: -62.18
Morne aux Diables: Latitude: 15.612 Longitude: -61.43
Pelee: Latitude: 14.82 Longitude: -61.17
Qualibou: Latitude: 13.83 Longitude: -61.05
Use a different symbol than what was used for earthquake locations to plot each of these 5 volcanoes on your plan-view map. Next, plot the volcanoes on the cross-section-view map, using zero as the depth so that all the volcanoes are correctly located at the surface.
Once the maps are complete, observe the relationship between the earthquakes and volcanoes. Formulate a claim about your observations that explains why the volcanoes are where they are. Think carefully about the evidence needed to support or refute your claim.
Map 1. Map view / Plan view of the Lesser Antilles area for plotting earthquake and volcano locations. Land surface is colored brown, and ocean is colored blue.
Map 2. Cross-section view of the Lesser Antilles. Land surface is colored brown, and ocean is colored blue. The y-axis indicates the depth beneath the Earth’s surface in kilometers. Note that the ocean depth is exaggerated greatly in order to enable it to be shown on this map.
Directions for creating the earthquake catalog for the Lesser Antilles
(data are provided in LAntillesdata.xls)
Part 1: making the map view image
- Go to the USGS earthquake catalog rectangular area search page:
- Input top and bottom latitude for your area: (18, 13)
- Input left and right longitude for your area: (-67, -57)
- Starting Date: about 6 months ago
- Ending Date: today
- Leave all the other boxes alone
- Click “Search.” See below for a screen capture example.
- You will get a screenful of some columns of numbers. For plotting on your plan-view map, the most important columns are the ones labeled LAT and LON. These are latitude and longitude.
- On Grid #1, plot each (longitude, latitude) pair.
Part 2: making the cross-section view image
After you are done plotting longitude and latitude, we are going to do a narrower search to make a good cross-section. Directions for the cross-section map:
- Go to the USGS earthquake catalog rectangular area search page:
- Input top and bottom latitude for your area (49, 47).
- Input left and right longitude for your area (146, 156).
- Starting Date: about 3 years ago.
- Ending Date: today
- Leave all the other boxes alone.
- Click “Search” See below for a screen capture example.
- You will get a screenful of some columns of numbers. For plotting on your cross-section, the most important columns are the ones labeled LON and DEP. These are longitude and depth.
- On Grid #2, plot each (longitude, depth) pair.
Lesser Antilles Instructor Key
Subduction Zone Geometry in Three Dimensions: Using the USGS earthquake catalog to explore the relationship between earthquakes, volcanoes, and plates at convergent margins.
Plan view map
Cross-section map
Catalog file used to produce the plan-view map
Subduction Zone Geometry – Eliza Richardson (2013)
LAT LON DEP
17.69 -61.69 27
17.95 -65.97 7
17.03 -61.47 16
16.65 -61.17 10
17.93 -65.85 7
17.89 -65.20 22
13.41 -58.41 97
14.27 -60.31 7
17.92 -63.72 57
17.86 -65.85 3
17.87 -65.86 5
17.96 -66.87 4
14.99 -60.74 61
17.93 -66.87 14
15.09 -61.18 147
14.23 -60.97 119
17.94 -64.29 8
17.89 -63.91 10
18.00 -59.65 34
17.91 -66.78 5
17.64 -65.96 23
17.86 -66.65 5
17.94 -64.91 8
13.19 -57.89 10
16.05 -60.89 29
18.00 -65.98 14
17.94 -65.85 24
17.94 -64.98 184
17.13 -61.15 22
17.99 -66.46 12
17.41 -61.53 32
17.94 -64.97 34
Subduction Zone Geometry – Eliza Richardson (2013)
Catalog file used to produce the cross-section map
Subduction Zone Geometry – Eliza Richardson (2013)
LAT LON DEP
14.94 -61.13 158
14.05 -60.65 15
14.00 -60.46 29
13.26 -60.73 105
14.94 -60.33 124
14.52 -60.60 6
14.93 -60.59 19
14.01 -60.99 20
14.99 -60.59 68
13.84 -61.17 5
14.82 -61.39 172
14.68 -61.05 22
14.92 -60.62 21
14.82 -60.85 76
14.76 -61.24 166
13.86 -60.29 11
13.95 -60.94 16
13.26 -60.72 49
14.53 -61.14 118
14.38 -59.13 10
14.58 -60.40 85
14.52 -60.18 43
14.89 -60.87 63
13.03 -61.07 243
14.37 -60.53 27
14.69 -61.12 24
13.39 -60.56 33
14.98 -61.08 140
14.01 -60.89 13
13.37 -60.59 27
13.16 -59.10 3
13.08 -60.82 51
14.19 -60.99 19
14.62 -60.81 34
14.74 -59.90 142
14.85 -60.96 102
14.41 -59.40 26
14.59 -60.20 167
13.61 -60.92 19
14.22 -60.68 77
13.84 -60.46 13
13.05 -60.74 89
14.94 -60.20 35
14.79 -61.01 83
14.89 -59.93 57
14.84 -61.36 146
13.60 -61.03 27
13.68 -60.80 9
13.86 -60.44 16
13.82 -60.41 23
13.81 -60.67 25
13.79 -60.49 13
13.84 -60.44 26
14.03 -60.48 30
13.92 -60.45 21
13.86 -60.41 16
13.72 -60.44 30
13.77 -60.49 16
14.83 -61.07 155
13.93 -58.58 20
13.40 -58.78 19
14.26 -58.69 34
14.31 -58.70 33
14.16 -61.06 35
14.16 -59.19 24
13.95 -60.56 24
14.10 -60.93 19
13.91 -60.34 26
14.04 -60.10 70
14.84 -61.41 182
13.87 -60.31 27
13.87 -60.33 27
14.10 -59.40 31
14.27 -59.54 53
13.41 -58.41 97
14.27 -60.31 7
14.99 -60.74 61
14.23 -60.97 119
13.19 -57.89 10
Subduction Zone Geometry – Eliza Richardson (2013)