Activity 3: Determining Earthquake-Induced Landslide Potential

Purpose
In this activity, students will use a geologic map of the La Crescenta area and slope inclination data, which are derived from the topographic map and their topographic model, to determine the possibility of earthquake-induced landslides in the region.

Materials
Each group of students will need:

• Geologic map of the Sierra Madre Fault Zone (Student Packet page 8),
• Topographic map (Student Packet page 7) and student-made topographic model,
• Table: Geologic environments likely to produce earthquake-induced landslides in the Los Angeles region (Student Packet page 6) (adapted from USGS Professional Paper 1360), and
• Table: Standard size classes of sediment.

Procedure

1. Provide students with copies of the materials listed above. Briefly explain to students what kind of information each of the materials (tables, model, maps) contains. For example, explain to students that a geologic map shows what materials are exposed at the surface.
2. Have students study the geologic map and the two tables. Ask students to locate the geologic environments listed in the table on the map.
3. Discuss the sediment-size table with the class. Explain that the table shows how geologists classify large and small sediments. Consider bringing in samples of the smallest sediments and creating mock pebbles, cobbles, and boulders out of wadded newspaper or paper-filled trash bags.
4. Have students use the tables, geologic map, and topographical model to answer the following questions about slope, geologic materials, and the risk of earthquake-induced landslide: Where is the landslide hazard the lowest? Where is the hazard the highest? What kinds of landslides are likely to occur in this region?
5. Have students mark the topographic map "Highest Landslide Risk," etc., as they answer these questions in Step 4. 6. Present students with the following scenario: It's February 1998. There's been an earthquake along the Sierra Madre Fault, magnitude 7.0 on the Richter scale. Have students find the Sierra Madre Fault on the geologic map. Then ask them to identify the locations where earthquake-induced landslides are likely to occur.
6. To connect this extended map interpretation activity to the Focus Question, ask students, "Based on the information in the geologic environments table, what can you predict about the potential for earthquake-induced landslides in the La Crescenta area?"

Extension

• Students could predict what would happen in the La Crescenta region if an earthquake occurred right after a heavy rain.
• Students could develop a susceptibility map and use it to answer the Focus Question in their final presentations.

Topographic map of model area (Activity 2). Create your own landslide hazard map. Use this topographic map to mark locations where you believe landslide risk is high or low.