Download Earthquake California - Berkeley County Schools

Earthquake California: An investigative look at the forces behind plate tectonics.
Guiding Question: Will part of California eventually, over time break off into the Pacific Ocean? Explain.
Background Research: California
Before you read the article, think about the following:
 How fast are the plates moving?
 Where is the fault located?
 What direction are the plates moving? Is there any evidence about rocks to support your thinking?
The San Andreas Fault is the boundary between the Pacific Plate and the North American Plate. It slices
California in two sections from Cape Mendocino to the Mexican border. San Diego, Los Angeles and Big Sur
are on the Pacific Plate, while San Francisco, Sacramento and the Sierra Nevada are on the North American
Plate. Despite San Francisco’s legendary 1906 earthquake, the San Andreas Fault does not go through the
city, however communities like Desert Hot Springs, San Bernardino, Wrightwood, Palmdale, and Bodega Bay
lie squarely on the fault and are sitting ducks.
The plates are slowly moving at a few centimeters a year, which is about the same rate that your fingernails
grow. This is not a steady motion, it is the average motion. For years the plates will be locked with no
movement at all. Suddenly the built-up strain breaks the rock along the fault and the plates slip a few feet all at
once. The breaking rock sends out waves in all directions and it is the waves that we feel as earthquakes.
In many places like the Carrizo Plain (San Luis Obispo County) and the Olema Trough (Marin County), the
fault is easy to see as a series of scarps and pressure ridges. In other places, it is more subtle because the
fault hasn’t moved in many years and is covered with alluvium, or overgrown with brush. In San Bernardino
and Los Angeles Counties, many of the roads along the fault cut through great mountains of gouge, the
powdery, crumbled rock that has been pulverized by the moving plates.
The hallmark of the San Andreas Fault is the different rocks on either side of it. Being about 28 million years
old, rock from great distances have been juxtaposed against rocks from very different locations and origins.
The Salinian block of granite in central and northern California originated in Southern California, and some
even say northern Mexico.
My Notes:
University Research: Types of plate boundaries
 Read through the passage, and complete the CDT (Convergent, Divergent, Transform) Table
on the following page.
There are three major ways plates can interact with one another. They could diverge, meaning they can move
away from one another resulting in a divergent plate boundary, they can converge, meaning they move
towards one another resulting in a convergent plate boundary, or they can move parallel to one another,
resulting in a transform plate boundary. Each of these different interactions results in different consequences
for Earth’s continental crust.
The most common divergent boundaries
are mid-ocean ridges. Shallow
earthquakes and minor, basaltic lava flows
characterize divergent boundaries at midocean ridges. The seafloor at the ridges is
higher than the surrounding plain because the rocks are hot and thus less dense and more buoyant, riding
higher in the underlying mantle. As the rocks move away from the spreading center, they cool and become
denser and less buoyant. Typically, these types of plate boundaries only produce around 5% of all seismic
energy released in a given year and recently determined that they have a moderate amount of volcanic activity.
Convergent boundaries are the most geologically active, with different features depending on the type of crust
involved. Typically, 90% of all seismic energy released by Earthquakes is resulted from convergent plate
boundaries. These earthquakes tend to occur deeper in the crust than at other boundaries. There are different
types of convergent plate boundaries, which are explained below.
Oceanic meets continental are subduction zones, where dense oceanic crust is diving beneath more buoyant
continental crust. These boundaries are characterized by a very deep ocean trench next to a high continental
mountain range, large numbers of earthquakes and large numbers of volcanoes. Oceanic meets more oceanic
occur when two plates converge along a boundary where the crust on both sides is oceanic, a subduction zone
also occurs, but the result is slightly different. Since the densities of the two plates are similar, it is usually the
plate with the older oceanic crust that is subducted (goes under) because that crust is colder and denser.
Earthquakes progress from shallow to deep moving away from the trench like in the oceanic-continental
convergence, and volcanoes form an island arc. Continental meets continental occurs when two pieces of
continental crust converge, the result is a great pileup of continental material. Both pieces of crust are buoyant
and are not easily subducted, resulting in large mountain ranges.
Transform plate boundaries occur when 2 plates move horizontally past one another. This is a very rare
occurrence on continents and makes up only about 5% of all seismic energy released in any given year. Not
many volcanoes are found in this region due to the movement of the plates and most earthquakes that occur
are very shallow. A transform plate boundary is typically marked in some places by linear valleys along the
boundary where rock has been ground up by the sliding. In other places, transform boundaries are marked by
features like stream beds that have been split in half and the two halves have moved in opposite directions.
While completing the chart below, fill in what features you would find at these types of boundaries
Convergent
Divergent
Transform
USGS Research: Data
You are provided with data for 3 locations, Chili in South America (Pacific Ocean side of South America),
Reykjanes Ridge (In the Atlantic Ocean, North to Iceland), and California. All data shown indicates every
major earthquake in the region with a magnitude of 6.5 or greater from 1930 – 2014.
Location
Number of Earthquakes
Average Depth
Average Magnitude
Chili, South America
113
54 km
7.0
Reykjanes Ridge, Iceland
4
16 km
6.7
California, United States
13
7 km
6.8
Geological Survey (Map) Data
Figure 1 to the left shows the area of Chili studied for this data set in table 3. Each triangle
indicates an active volcano along the fault zone.
Figure 2 (below) shows the current active volcanoes in the California region. Each dark
triangle indicates an active volcano. Pay attention to the linear valley (Sierra Nevada
Mountains) along the location near the San Andreas Fault- it aligns with the volcanoes.
Figure 3 to the right indicates all tectonic plates and their names for reference. The locations of these plates have
changed over the years due to continental drift as a result of
earthquakes. 200-300 million years ago, the Earth’s surface
looked quite different, known as Pangea. All of the continents at
this time were combined, forming one super-continent.
Figure 4 to the left shows the
location of Iceland in the middle of
the Atlantic Ocean. Running
through the middle of the island is
the Reykjanes Ridge, which is part of
a mid ocean ridge. A mid ocean
ridge occurs when two oceanic
plates are at a divergent plate
boundary.
Figure 5 (above) is from the USGS, indicating the average depth of all earthquakes from 1975-1995.
Investigative Reporting from National Geographic
Rift Valley versus Mid-Ocean Ridges
A rift valley forms where the Earth’s crust, or outermost layer, is spreading or splitting apart. This kind
of valley is often narrow, with steep sides and a flat floor.
Rift valleys differ from river valleys and glacial valleys because they are created by tectonic activity and not by
the process of erosion.
Rift valleys are created by plate tectonics. Tectonic plates are the huge rocky slabs made up of the Earth's
crust and upper mantle. Where plates move apart, the Earth’s crust separates, or rifts. Rift valleys can lead to
the creation of entirely new continents, or deepen valleys in existing ones.
Many rift valleys have been found underwater, along the large ridges that run throughout the ocean.
These mid-ocean ridges are formed as tectonic plates move away from one another at divergent plate
boundaries. As the plates separate, molten rock from the Earth’s interior may well up and harden as it
contacts the sea, forming new oceanic crust at the bottom of the rift valley. In order for a rift valley to be
considered a mid-ocean ridge, it must be a divergent plate boundary at 2 oceanic plates.
This occurs along the northern crest of the Mid-Atlantic Ridge (Reykjanes Ridge), where the North American
plate and the Eurasian plate are splitting apart. The Mid-Atlantic Ridge rifts at an average of 2.5 centimeters (1
inch) per year. Over millions of years, the Mid-Atlantic Ridge has formed rift valleys as wide as 15 kilometers (9
miles).
In the Pacific Ocean, the East Pacific Rise has created rift valleys where the Pacific plate is separating from the
North American plate, Riviera plate, Cocos plate,
Nazca plate, and Antarctic plate. (The Pacific plate
is
the largest on Earth.) Like many underwater rift
valleys, the East Pacific Rise is dotted
with hydrothermal vents. The geologic activity
beneath the underwater rift valley creates these
vents, which spew super-heated water and
sometimes-toxic vent fluids into the ocean.
There are only two rift valleys on Earth
within continental crust, the Baikal Rift Valley and
the
East African Rift (Right). Tectonic activity splits
continental crust much in the same way it does along mid-ocean ridges. As the sides of a rift valley move
farther apart, the floor sinks lower.
The deepest continental rift valley on Earth is the Baikal Rift Valley in the Siberian region of northeastern
Russia. Lake Baikal, the deepest and oldest freshwater lake in the world, lies in the Baikal Rift Valley. Here, the
Amur plate is slowly tearing itself away from the Eurasian plate, and has been doing so for about 25 million
years. The deepest part of Lake Baikal is 1,187 meters (3,893 feet), and getting deeper every year. Beneath
this is a layer of soft sediment reaching several kilometers. The actual bottom of the rift extends about 10
kilometers (6.2 miles) deep.
 So, what is the difference between a rift valley and a mid-ocean
ridge? (This question will be on your quiz.)
Research Expectations
Your group is to furnish a report, answering the guiding question, “Will part of California eventually, over time
break off into the Pacific Ocean?” Your report must include only data derived from the previous 6 pages of
information including the background research, university research, USGS Data, Geological Survey Data, and
Investigative Reporting Data. *No other outside sources may be used.* All of your statements must be
supported by data included on those 4 pages. Speculation and opinion are not allowed. Your report must
follow the claim/evidence/justification model as indicated below.
Your Report
Guiding Question: Will part of California eventually, over time break off into the Pacific Ocean?
Our Claim: This is where your answer to the question goes after completion of lab.
Evidence:
Justification:
All data collected over the course of the lab
goes in this box. This data can include (but
not limited to)
Why your claim is correct in paragraph
form while reflecting on the data. You MUST
connect the evidence to your answer!

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Data from data tables (you may not
want the entire data table, but you
could average the data or make a
generalization)
Data from Maps (You can copy a
section of the map and highlight it
here)
Key pieces of data from the
readings
Background research about
California
The following KEY VOCABULARY must be
included:

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Convergent
Divergent
Transform
Mid-ocean ridge
Sea floor spreading
Volcanoes or Mountain Building
Plate Tectonics