Lab 4.2

* This data lab is under construction and has not yet been published. We anticipate releasing this edition of the plate tectonics data lab before December 1, 2025 *

Lab 4.2 – Earthquakes and Plate Boundaries

Fundamental concept: Recognize the relationship between bathymetry and earthquakes and connect real-world relationships to background knowledge.
Estimated time to complete: 20 minutes
Data skills preparation: Lab 1.2 geography, Lab 2.3 – Bubble Charts
Materials needed: Computer

Earthquakes, or the sudden shaking of the ground that occurs when rocks beneath the surface break and slide past one another, are one of the most common geological phenomena on Earth. In fact, thousands of earthquakes occur each year! Most earthquakes are small and go unnoticed by people, but some earthquakes cause severe shaking which can cause loss of life and property.

Earthquakes can occur for many reasons, including volcanic activity and landslides amongst other phenomena, but the most common cause for earthquakes is the movement of rocks relative to one another along broken surfaces in rock called faults. You have likely noticed that earthquakes are commonly clustered along plate boundaries. This is because faults are commonly clustered along plate boundaries. Movement along a fault causes a release of seismic energy in waves that radiate out in every direction from the location of the earthquake, gradually dissipating with distance. The amount of energy released, called the magnitude of the earthquake, depends on how much movement there is along a fault, and generally speaking, the greater the magnitude, the greater the shaking! The energy waves produced by an earthquake move outward in every direction from the location of the earthquake. An excellent analogy is to think of the waves that form on the surface of a glass of water if disturbed by a falling drop of water. They ripple outward, with the ripples getting wider and wider, yet as they widen, less energy is present at any given location.

When you hear about earthquakes on news, you often hear the term epicenter, which is the location (such as a town) that is above the earthquake location at depth, which is called the hypocenter, or focus. Scientists are more interested in the hypocenter, which is always at some depth, ranging from a few kilometers to hundreds of kilometers. This is because earthquake depth can tell us about the geologic processes responsible for producing the earthquake, and because earthquake depth influences the severity of shaking and how people in nearby areas will experience the earthquake. This can help emergency response officials respond quickly and efficiently in the aftermath of an earthquake.

A map of South America showing locations of earthquakes along the western coast. The earthquakes range from shallow to deep. A second diagram shows a cross-section across the subduction zone with earthquake locations in both plates.

Earthquakes in South America are largely focused along a convergent plate boundary that parallels the West Coast. Here, the Pacific Plate is being subducted beneath the South American plate. Earthquake hypocenters are plotted on the map, revealing a pattern of gradually increasing depth with distance East of the subduction zone. Data along the profile line on the map, A – A’, is plotted on the right hand side of the figure. The earthquake hypocenters are concentrated in the subducting plate, revealing the plate’s location within the Earth’s mantle!

How to use the widget:

If you hover over the map and scroll with your mouse, the map will zoom in or out.
You may also use the zoom features on the left to zoom in/out of the area in a more controlled method.
You can move the map around by clicking and dragging it.
To overlay the age of the seafloor and the locations of tectonic plate boundaries, earthquakes and volcanoes, toggle these layers on by [de-]selecting the boxes beside the layer name.
Use the measurement tool (arrow button) to measure the distance between two locations of your choosing. Select the measurement tool, click a location on the map, and then click the second location to measure the distance. Select the “X” button to remove all measurements and to stop measuring additional distances.

**** INSERT MODIFIED WIDGET FROM LINK BELOW ****

https://datalab.marine.rutgers.edu/explorations/notebook3/lab3_tectonics1.htm

Quick Check Orientation Questions

For this part of the exercise we will turn on the earthquake layers in the widget below. Begin with only the layer “All Earthquakes, 0+, 30 days” clicked on. It shows the locations of all of the earthquakes that occurred globally over 30 days and is typical of what we see during most 30-day intervals.

Quick Check Questions – Part 2

For the next question, turn on the layer that shows plate boundaries and compare it to the earthquake locations. You may use the + and – buttons to zoom in and out to look at more details. At the bottom of the map on the widget you will notice a series of links that allows you to zoom in on various locations. Click on the various locations to get a better look. Once you have clicked, be sure not to zoom in or out so that you are looking at the correct area. To move to a different area, just click on the name of the new area.