Grade level: 9 and above, including college undergraduates
Performance Objective: Students will use strain model data with Google Earth to relate strain to crustal deformation and uplift.
Goal: To provide the student with first hand experience in developing and testing hypotheses
Background: Students who enage in these exercises should have a prior understanding of plate tectonics, earthquakes, and faults.
Equipment: Make sure Google Earth is installed on your machine and that KMZ files are set to open in Google Earth on the machine.
Click on the link to the Cities, Faults, and Topography dataset. Google Earth should start and the view should then zoom in on a particular part of the Earth.
What states are visible on the map after the view zooms in?
What country, in addition to the United States, is visible on the map?
Note that there is a scrollbar connected with the Places panel. Scroll down to the Strain Rate Model folder, if it is not visible in the Places panel. This folder contains additional folders - Cities, Faults, and Topography. Note that the square checkboxes act as toggles when they are clicked to make features on the map visible or invisible. Radio buttons, which are round, make one layer visible at a time from within a set.
Note that, as is indicated in the illustration of the Places pane to the right, when the link to the Cities, Faults, and Topography dataset is first clicked in a browser, and Google Earth launches, the Cities Now, Faults Now, and Topography Now layers all become visible. These represent the current configuration of the Earth's surface in the southern California area. The visibilities of the cities and faults are controlled by checkboxes, while the topography layers can be viewed one at a time through radio buttons.
The Plus (+) and minus (-) buttons to the left on the checkboxes expand and contract lists of items within folders. While a folder is in expand mode, the visibility of the items within the folder can be controlled through checkboxes or radio buttons.
In the Cities, Faults, and Topography dataset, the cities and faults connected with each of the six times reprented in the dataset are shown on the map as follows:
In the illustration to the right, points are shown representing the past positons of the location on the Earth's crust marked by Tehachapi, California are shown in the representative colors for each of these time frames. The time frames for the locations of faults are represented by the same colors, but only the current time frame is shown here.
The navigation controls can be used to choose the orientation of the map, the zoom level, and the tilt of the view. The compass controls the orientation of the map. Drag it in a circular direction to reorient the map. Click on the "N" to orient the map so that north is up.
The bar on the top controls the tilt. Double-click the box at the left end of the tilt slider to restore a straight down view of the map.
The bar on the right controls the zoom level.
|Above the Google Earth view window is a set of tools. The ruler tool, illustrated to the right, can measure distances between points on the map in the view window.||
|The units of measurement for the ruler can be chosen by using the pull-dowm menu in the ruler dialog box, shown to the right, that opens when the ruler is chosen. We will use kilometers in this exercise.||
Using the checkboxes in the Places pane, make sure that all the Cities folders are invisible. Expand the Cities Now and Cities 2,500,000 YBP (Cities 2,500,000 years before present) folders, in order to see the lists of cities in each. In both folders, make Santa Clarita and Santa Monica visible by using the appropriate checkboxes.
Click the Ruler to activate it and open the Ruler dialog box.
Measure the distance between the point marked by Santa Clarita 2,500,000 years ago (purple) to the point represented by Santa Monica 2,500,000 years ago (also purple) by clicking on one of these points on the map, and then the other. Make sure the units in the Ruler dialog box are set to kilometers, and write down the time frame along with the distance shown in the dailog box.
Do the same for Santa Clarita Now and Santa Monica Now, which are represented by red points and labels.
How has the distance between the points represented by these cities changed over time?
Now use the radio buttons to compare the topography for 2,500,000 YBP to the topography now in the vicinity of these cities.
Is your observation of the changes in the topography and elevation consistent with the change in the distance between the points represented by these two cities?
Using the checkboxes, make all cities invisible for all of the time frames.
For the Cities Now and Cities 2,500,000 YBP folders, make Sun City and Twentynine Palms visible.
Use the ruler to measure the distances that the points represented by these two cities moved.
Using the checkboxes, make all the faults visible for Now and for 2,500,000 YBP. Make the others invisible. Faults that are illustated as part of the topography layers will also remain visible on the map.
Note how the orientation of faults has changed over time, especially the ones that have a general east-west orientation. Have they rotated clockwise or counterclockwise?
Also observe how the topography has changed over time by using the radio buttons to look at the topography layers for each time frame.
How do your observations relate to the fact that Sun City and Twentynine Palms are on opposite sites of a plate boundary characterized by right-lateral motion?
How do the changes in orientation of the faults relate to the plate boundary?