Earthquakes in Subduction Zones

Distance
(km)
Latitude
(° N)
Depth
(km)
10 46.0 50
20 47.2 40
30 45.5 80
50 48.0 100
60 47.0 110
80 49.0 100
100 47.5 10
120 49.0 145
120 48.5 60
130 46.2 140
160 48.8 230
200 47.8 280
220 49.0 280
230 48.2 300
240 46.5 320
250 47.5 310
270 49.0 380
310 45.2 420
320 48.0 440
320 47.8 430
340 48.2 460
350 46.5 520
360 47.5 540
360 45.0 550
380 47.0 530
400 48.0 580

Background:

Geophysicists discovered that when the locations of earthquakes near ocean trenches were plotted, an interesting pattern appeared. This pattern helped support theories regarding subduction of tectonic plates and deep focus earthquakes. Deep focus earthquakes are earthquakes that originate between 300 and 700 km below the earth's surface. They saw that the depth of earthquakes changes with increasing distance from an ocean trench. In this investigation, you will plot the locations of earthquakes in three dimensions so you can "see" a subducting plate at a convergent plate boundary.

Procedure:

  1. The chart shows earthquake foci arranged by distance from the trench, depth of the earthquake, and latitude.
  2. On the first graph, plot the earthquake's distance from the trench versus the earthquake's depth.
    1. Plot the earthquake distance from the trench on the x-axis.
    2. On the y-axis, plot the earthquake depth. Start numbering with zero km at the top of the graph.
  3. On the second graph, plot the earthquake's distance from the trench versus the earthquake's latitude.
    1. Plot the earthquake distance from the trench on the x-axis.
    2. On the y-axis, plot the earthquake latitude.
    3. Use three different symbols or colors when plotting the earthquakes.
      • SHALLOW earthquakes (0 to 70 km depth) - use one symbol or color.
      • MEDIUM DEPTH earthquakes (70 to 300 km) - use a different symbol or color.
      • DEEP FOCUS earthquakes (300-700 km) - use a third symbol or color.
  4. On both graphs, be sure to label each axis, specify the units used, create a descriptive title and provide a legend or key for the depth symbols or colors (if needed).

Analysis:

(answer in complete sentences)
  1. What is the relationship between an earthquake's distance from the trench and the depth of the earthquake?
     


  2. How does this relationship pertain to plate tectonics? Be specific and use the correct terminology.
     





 

Graph 1


 
 

Graph 2