Name: ___________________________ Class: ________________ Date: ___________

 

Fault Extent Student Exercise

 

INSTRUCTIONS:

Plotting the Major California Faults

Faults are not always exposed at the Earth's surface, but are sometimes covered by buildings, trees, or soil and sediments that have been moved by rivers and landslides. To determine the locations of active faults, geologists travel around mapping rock "outcrops" (where rock is exposed at the surface) and recording the location of faults where they observe them. Locations on earth are usually recorded as latitudes and longitudes.

Remember: "Latitude" measures position from north to south. It is a positive number in the northern hemisphere. "Longitude" measures positions from east to west across the globe, and it is negative in the western hemisphere.

Your job is to take the coordinates recorded by the field geologist and plot them on a map to determine the location of active faults in California.

  1. To begin, use the information in the Major California Faults data table and plot the coordinates of the San Gregorio fault by placing a dot at the longitude and latitude of each of the 4 points. If a coordinate goes off the edge of your map, just ignore it.
  2. Connect the dots for the San Gregorio fault. Be sure to use a ruler or straight edge to make a straight line between each pair of dots. Label the lines with the words, "San Gregorio fault." Geologists usually use red lines for faults, but you can use your favorite color.
  3. Repeat this process for each of the other faults. You should end up with 8 lines, some of which connect to one another.

Plotting Typical Earthquakes

Even though big earthquakes cause the most damage, scientists monitor earthquakes of all sizes – even ones that are too small to feel. Learning about the patterns of the many small earthquakes helps them predict where the few big ones will occur. They use seismometers to determine the location where each earthquake starts. They call this location the epicenter, and they record its position in latitude, longitude, and depth below the surface.

Your job is to plot the location of these real earthquakes on the same map as the active faults.

  1. Using the information in the California Earthquakes data table, plot the coordinates of each earthquake epicenter by placing a dot at the latitude and longitude of each point.

 

What do you see?

Answer the following questions about what you see:

  1. Which direction do most of the faults go (north, south, east, west, etc…)? Do they all go the same direction? Why do you think this might be?
  1. Where do most of the earthquakes occur? Why? Are there exceptions? Why?
  1. Find the earthquake that occurred on April 18, 1906. What was its magnitude? Is this bigger or smaller than most of the earthquakes in this list? Mark its epicenter with a star, and write '1906' next to it. Which fault did this earthquake rupture?
  1. The 1906 earthquake started at the epicenter you marked with a star, but scientists observed fault offset (like the offset fences in the slide show) along a huge section of the California coast, from Cape Mendocino in the north to as far south as San Juan Bautista. What is the distance, in kilometers, from the earthquake epicenter to Cape Mendocino? What is the distance form the epicenter to San Juan Bautista? What is the total length that this fault ruptured? Draw a grey line along the entire rupture length and label it "1906 Earthquake rupture".
  1. Find the earthquake that occurred on May 3, 2002. On which fault did this earthquake occur? What was its magnitude? This earthquake was barely felt by anybody except students at the University of California at Berkeley. The earthquake occurred directly below the campus football stadium, which is cut by a major fault (the earthquake was in the middle of the night, so nobody was playing football at the time). The earthquake rupture was, coincidentally, about the same size as the football field (about 100 meters). The earthquake caused a patch of fault the size of a football field to slip. What is 100 meters in kilometers? On your map, how many inches across is a 100 meter long line? (this is sort of a trick question).
  1. Write one sentence comparing the size of the 1906 and 2002 earthquake rupture lengths.
  1. Based on the information about these two earthquakes, write a sentence explaining how earthquake magnitude is related to the length of the fault patch that ruptures in an earthquake.
  1. Can you tell anything about the magnitude of an earthquake from the location of its epicenter alone? Why or why not?

 

 

CALIFORNIA EARTHQUAKES

This list includes recorded earthquakes for the one week from July 13-19, 2005. Over 350 earthquakes greater than magnitude 1.0 were recorded during that period, so this is just a partial list. The list begins with two other interesting earthquakes from 1906 and 2002.

(From: http://quake.usgs.gov/recenteqs/latestfault_allframes.htm)

 

Date

Time

(Pacific)

Longitude

(°E)

Latitude

(°N)

Magnitude

April 18, 1906

5:12 AM

-122.5

37.7

7.8

May 3, 2002

11:44 PM

-122.2

37.9

2.0

July 13, 2005

2:38 AM

-121.7

37.4

1.4

July 13, 2005

4:55 AM

-118.1

36.2

3.1

July 13, 2005

9:26 AM

-121.0

35.7

2.4

July 13, 2005

2:34 PM

-121.6

36.9

2.0

July 13, 2005

2:36 PM

-121.8

37.7

1.3

July 13, 2005

2:54 PM

-122.1

37.8

1.5

July 13, 2005

4:53 PM

-116.4

32.3

2.3

July 13, 2005

5:09 PM

-125.0

40.4

3.1

July 13, 2005

7:15 PM

-116.1

34.7

3.1

July 13, 2005

7:24 PM

-121.9

37.8

1.8

July 13, 2005

7:32 PM

-116.1

34.7

3.1

July 13, 2005

7:57 PM

-119.2

35.0

1.6

July 14, 2005

7:38 AM

-121.1

36.5

1.4

July 14, 2005

12:21 PM

-122.1

37.3

2.0

July 14, 2005

8:09 PM

-121.6

36.9

1.5

July 15, 2005

8:19 AM

-124.4

40.3

2.9

July 15, 2005

10:56 AM

-118.8

34.8

1.1

July 15, 2005

1:00 PM

-121.6

36.9

2.1

July 15, 2005

5:08 PM

-119.0

34.9

2.0

July 15, 2005

9:58 PM

-116.3

34.8

3.8

July 15, 2005

11:46 PM

-116.3

34.8

3.5

July 16, 2005

10:44 AM

-121.6

36.1

1.7

July 16, 2005

10:56 AM

-121.7

37.3

1.4

July 16, 2005

2:28 PM

-123.2

38.6

1.2

July 17, 2005

12:10 AM

-120.4

35.9

2.6

July 17, 2005

1:41 AM

-122.6

37.7

1.7

July 17, 2005

10:43 AM

-121.1

36.5

1.9

July 17, 2005

6:22 PM

-116.6

33.5

2.7

July 18, 2005

4:42 AM

-121.6

37.2

1.7

July 18, 2005

4:48 PM

-120.6

36.1

2.7

July 18, 2005

10:02 PM

-118.5

34.3

1.5

July 19, 2005

12:45 AM

-118.6

34.5

2.2

July 19, 2005

3:29 PM

-122.5

37.5

1.9

 

 

MAJOR CALIFORNIA FAULTS

 

Fault Name

Longitude

(°E)

Latitude

(°N)

San Gregorio

-122.7

37.9

-122.3

37.0

-122.0

36.5

-121.4

35.8

San Andreas

-124.2

40.3

-123.7

39.0

-123.5

38.8

-122.7

37.9

-122.2

37.3

-121.8

37.0

-119.4

34.9

-116.2

33.8

-115.0

32.4

Rodgers Creek

-123.6

39.8

-123.0

38.8

-122.5

38.1

Hayward

-122.4

38.0

-121.7

37.3

Calaveras

-122.0

37.8

-121.5

37.0

Concord/Green Valley

-122.2

38.4

-121.9

37.9

Mt. Diablo Thrust

-121.9

37.9

-121.7

37.8

Greenville

-121.7

37.8

-121.7

37.6

 

DLESE Teaching Boxes | October 2005