Instructions: First print copies the Lag-time questions and Real-time questions. You may also choose to copy this part of the voyage (text and images). Read the text, examine the images, and write answers to the questions on your copies. When you are satisfied with your answers, submit them online.
Don't forget to check out the course web site where you can obtain preparatory information before each class and summaries that are posted after the class meets. Click here to bring up a new browser window with the course site. You can also use this site to display the text and images part of the voyage on a second window so that you don't have to print anything.
Figure 1. This map shows earthquakes that occurred on Earth in a 20-year period, between 1975 and 1995. Earthquakes occur beneath the Earth's surface, at depths of several kilometers (km) to hundreds of km. For this map view, earthquake epicenters are projected upward onto the Earth's surface. Earthquake depths are shown by color-coding (in km): brown = 0-33 km depth; yellow = 33-71 km depth; green = 71-151 km depth; blue = 151-301 km depth; magenta = 301-501 km depth; red = 501-800 km depth.
Figure 2. This map shows earthquakes that occurred in the western part of the United States and the northwestern part of Mexico during the same 20-year period. As in Figure 1, earthquakes are projected onto the Earth's surface and color-coding shows their depths.
Now let's go to a bulletin of near-real-time earthquakes, to see where earthquakes have occurred during the past day or two. Click here to go to the U.S. Geological Survey's National Earthquake Information Center (USGS-NEIC). This page includes both a list of earthquakes and a map with those earthquakes' locations. Choose an earthquake from either the list or the map and click on that earthquake to get more information.
We all know that earthquakes are a fact of life in California and the San Francisco Bay Area. The Association of Bay Area Governments (ABAG) has an informative web site that includes maps of earthquake intensity based on the geologic materials at different locations and on the proximity of these locations to various Bay Area faults.
Figure 3. This map shows the expected intensity of earthquake shaking in the Bay Area, based on the type of underlying geologic material (for example: stable bedrock, fractured bedrock, consolidated sediment, unconsolidated sand or mud).
Figure 4. This map shows the expected intensity of earthquake shaking in San Francisco, based on the type of underlying geologic material. If you want to see a detailed map of another Bay Area city, click here to go to the ABAG site. In the left box, click on the city of interest; in the right box, click on materials; then click "view map".
Earthquakes are strong evidence that pieces of Earth shift around with respect to other pieces. In the 1950s and 60s, geoscientists examined many types of evidence as they tried to figure out a theory to systematically explain this mobility. We will examine some other types of evidence in class. One additional example is illustrated below.
Figure 5. This map shows seafloor ages in color-coding. Red colors = 0-10 million years (my); brown colors = 10-40 my; yellow colors = 40-70 my; green colors = 70-120 my; light-blue colors = 120-150 my; dark-blue colors = 150-180 my. Ages refer to the time when basaltic lava flowed from volcanoes to form the seafloor. Usually, the basaltic crust is covered by younger sediments that rain down to the seafloor through the overlying water column. Cores can be drilled through the sediment cover to obtain samples of the underlying lava, which is then dated by chemical methods.