Page 65 - Laboratory Manual in Physical Geology

ACTIVITY ACTIVITY

2.6 Using Earthquakes to 2.7 San Andreas Transform-
Identify Plate Boundaries Boundary Plate Motions

THINK | How are plate boundaries identified? THINK | How are plate boundaries identified?
About It How and at what rates does plate About It How and at what rates does plate
tectonics affect Earth’s surface? tectonics affect Earth’s surface?
OBJECTIVE Apply earthquake data from South OBJECTIVE Analyze maps of geology and GPS-
America to define plate boundaries, identify plates, based plate motion vectors data to determine

construct a cross section of a subduction zone, absolute and relative plate motions along the San
and infer how volcanoes may be related to plate Andreas Fault to transform boundaries.
subduction.
INTRODUCTION California’s San Andreas Fault is
INTRODUCTION Earthquakes occur at depths of a boundary between the Pacific and North American

0–700 km inside Earth. Most occur along the mobile lithospheric plates. Movement along the plate
boundaries between plates (inter-plate earthquakes), boundary can be characterized and measured using
which enables geologists to map the plate boundaries geologic maps that show how rock units have been
as linear zones of abundant earthquake activity. offset (cut by the fault and separated in distance)
Earthquakes occur with less frequency within the by plate movement along the fault. GPS (Global
rigid plates themselves (intra-plate earthquakes). The Positioning System) data reveals strain (deformation)
exact location where rocks break and displace (slip patterns caused by absolute motions of the plates.
past one another) to make an earthquake is called the
focus of the earthquake. Shallow focus earthquakes PROCEDURES
(0–69 km deep) are the most common kind of 1. Before you begin , read about the GPS time series
earthquakes and occur at all three main kinds of plate below. Also, this is what you will need to do the
boundaries (divergent, convergent, and transform: activity:
FIGURE 2.2 ). Intermediate (70–299 km deep) and deep ____ calculator, ruler

focus earthquakes (300–700 km deep) occur mostly ____ Activity 2.7 Worksheets (pp. 66 – 67 ) and pencil
in Wadati-Benioff zones of earthquake activity 2. Answer every question on the worksheet in a
associated with plate subduction at convergent plate way that makes sense to you and be prepared to
boundaries ( FIGURE 2.2 ).
compare your work and inferences with others.
PROCEDURES
1. This is what you will need to do the activity:
____ red pencil or pen
____ ruler ACTIVITY
____ Activity 2.6 Worksheets (pp. 64 – 65 ) and pencil
2.8 Hot Spots and Plate Motions
2. Answer every question on the worksheet in a
way that makes sense to you and be prepared to
compare your work and inferences with others. THINK | What are hot spots, and how do they
About It help us explain plate tectonics?

OBJECTIVE Determine rates and directions of plate

motions as they have moved over hot spots.
PROCEDURES

Evaluating Plate Tectonics and 1. Before you begin , read about plate tectonics and
hot spots below. Also, this is what you will need
Hot Spots to do the activity:
The Plate Tectonics Model is widely applied by geo- ____ calculator, ruler
scientists to help explain many regional and global ____ Activity 2.8 Worksheets (pp. 68 – 69 ) and pencil
features of the geosphere. Another regional feature
2. Answer every question on the worksheet in a
of Earth is hot spots, centers of volcanic activity that
way that makes sense to you and be prepared to
persist in a stationary location for tens-of-millions of
compare your work and inferences with others.
years. Geologists think they are either a) the result of

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