Data and Graphs: Analyzing Plate Tectonics Evidence
Learn
Scientists use data from many sources to understand plate tectonics. In this lesson, you will learn to read and interpret scientific data presentations commonly used in earth science research.
Types of Data in Plate Tectonics Research
1. Earthquake Data
Seismologists measure earthquakes using the Richter scale (magnitude) and record their depth and location. This data reveals plate boundary locations and types:
- Shallow earthquakes (0-70 km) occur at all boundary types
- Deep earthquakes (70-700 km) only occur at subduction zones
- Earthquake frequency maps outline plate boundaries
2. GPS Measurements
Global Positioning System (GPS) stations measure plate movement with millimeter precision. Scientists track:
- Direction of plate movement
- Rate of movement (typically 2-10 cm per year)
- Changes in movement over time
3. Seafloor Age Data
Magnetic stripes in oceanic crust reveal the age of the seafloor. Key patterns:
- Youngest rocks are found at mid-ocean ridges
- Rock age increases symmetrically away from ridges
- This pattern supports seafloor spreading theory
4. Volcanic Activity Records
Volcanic eruption data helps identify:
- Active plate boundaries (Ring of Fire)
- Hotspot locations (like Hawaii)
- Patterns in eruption frequency and intensity
Reading Scientific Graphs
When analyzing any scientific graph, follow these steps:
- Read the title - What is being measured?
- Identify axes - What variables are shown? What are the units?
- Look for patterns - Is there a trend? Are there clusters?
- Note scale - Are the intervals regular? Is it linear or logarithmic?
- Consider meaning - What does this data tell us about Earth?
Examples
Example 1: Earthquake Depth Data Table
Study this data table showing earthquake depths at different plate boundaries:
| Boundary Type | Location Example | Shallow (0-70 km) | Intermediate (70-300 km) | Deep (300-700 km) |
|---|---|---|---|---|
| Divergent | Mid-Atlantic Ridge | 85% | 15% | 0% |
| Transform | San Andreas Fault | 100% | 0% | 0% |
| Convergent (subduction) | Japan Trench | 45% | 35% | 20% |
Analysis: Only subduction zones have deep earthquakes because the descending plate carries earthquake-producing rock deep into the mantle. Transform boundaries have only shallow quakes because plates slide past each other at the surface.
Example 2: Plate Movement Rate Graph
Consider this data showing the Pacific Plate's movement rate over 50 years:
| Year | Movement (cm/year) |
|---|---|
| 1970 | 7.2 |
| 1980 | 7.1 |
| 1990 | 7.3 |
| 2000 | 7.0 |
| 2010 | 7.2 |
| 2020 | 7.1 |
Analysis: The Pacific Plate moves at a relatively constant rate of about 7 cm per year. Small variations are within measurement uncertainty. This consistency supports the theory that mantle convection provides steady driving force for plate motion.
Example 3: Interpreting a Seafloor Age Map
Seafloor age maps use colors to show rock ages:
- Red/orange = youngest (0-20 million years old)
- Yellow/green = intermediate (20-80 million years old)
- Blue/purple = oldest (80-180 million years old)
Key observation: The youngest seafloor forms symmetric stripes along mid-ocean ridges, providing evidence that new crust forms at divergent boundaries and spreads outward.
Practice
Use your data analysis skills to answer these questions.
1. A scientist measures that a GPS station in California moved 15 cm over 3 years. What is the average rate of plate movement in cm/year?
2. Looking at the earthquake depth data table, why do you think transform boundaries only have shallow earthquakes?
3. The following data shows earthquake counts at different locations in one year:
- Location A: 450 earthquakes
- Location B: 12 earthquakes
- Location C: 380 earthquakes
Which locations are most likely near plate boundaries? Explain your reasoning.
4. If seafloor near a mid-ocean ridge is 0 million years old and seafloor 350 km away is 10 million years old, calculate the rate of seafloor spreading in km per million years.
5. A student claims that deep earthquakes prove plates are moving faster at subduction zones than at transform faults. Is this reasoning correct? Why or why not?
6. The table shows volcanic eruptions per decade along different plate boundaries:
| Boundary | Eruptions/Decade |
|---|---|
| Ring of Fire (convergent) | 75 |
| Mid-Atlantic Ridge (divergent) | 45 |
| San Andreas Fault (transform) | 0 |
Explain why transform boundaries have no volcanic activity based on what you know about plate motion.
7. Scientists measured that Japan moved 2.4 meters toward North America during a major earthquake in 2011. How does this sudden movement compare to typical annual plate motion of about 8 cm/year?
8. A graph shows that Hawaii is moving northwest at 7 cm/year, while a hotspot beneath it stays stationary. If a new volcanic island began forming today, how far from the current Big Island would it be in 1 million years?
9. Examine this earthquake depth distribution:
- Location X: 95% shallow, 5% intermediate, 0% deep
- Location Y: 40% shallow, 40% intermediate, 20% deep
Identify the most likely boundary type at each location. Support your answer with evidence from the data.
10. Why is it important for scientists to collect plate movement data from multiple GPS stations rather than just one? What could a single station miss?
Check Your Understanding
Reflect on these questions to assess your learning.
- Can you read and interpret a data table showing earthquake depths?
- Can you calculate rates of plate movement from distance and time data?
- Can you explain what patterns in seafloor age tell us about plate tectonics?
- Can you use data to support claims about plate boundary types?
Next Steps
- Practice interpreting graphs from scientific articles about earthquakes
- Look up real GPS data for a plate near your location
- Continue to the next lesson on writing scientific explanations using CER format