Download Earthquake Occurrences in Different Tectonic Settings

Earthquake Occurrences in different tectonic settings
Earthquakes occur around the globe within the lithosphere. Most earthquakes are generated
from interactions between plate boundaries. Therefore, the lines of earthquakes help define
the lithospheric plates and three types of plate boundaries: divergent, convergent and
transform.
Divergent Boundaries-Mid-Ocean Ridge System
Divergent boundaries occur along spreading centers where plates are moving apart and new
crust is created by magma pushing up from the mantle. Perhaps the best known of the
divergent boundaries is the Mid-Atlantic Ridge. This submerged mountain range, which
extends from the Arctic Ocean to beyond the southern tip of Africa, is but one segment of the
global mid-ocean ridge system that encircles the Earth. The rate of spreading along the MidAtlantic Ridge averages about 2.5 centimeters per year. Earthquakes within the divergent
boundaries are shallow, aligned strictly along the axis of spreading. Earthquakes in divergent
environments tend to be smaller than magnitude 8.
Transform Boundaries-San Andreas Fault
Transform boundaries occur along two plates that are moving side by side. Earthquakes are
shallow and tend to generate earthquakes smaller than magnitude 8.5. The San Andreas Fault
in California is a nearby example of a transform boundary, separating the Pacific from the North
American plate.
Convergent Boundaries-Himalayas
At convergent boundaries, when two continental plates meet head-on, neither is subjected
because the continental rocks are relatively light, and like tow colliding icebergs, resist
downward motion. Earthquakes are found in several settings ranging from the very near
surface to several hundred kilometers deep. The Himalayan mountain range dramatically
reveals how the rust tends to buckle and be pushed upward or sideways. The collision of India
into Asia 50 million years ago caused the Eurasian plate to crumple up and override the Indian
plate. After the collision, the slow continuous convergence of the two plates over millions of
years pushed up the Himalayas to their present height. The Himalayas, towering as high as
8,8545m above sea level from the highest continental mountains in the world.
Convergent Boundaries-The Ring of Fire
Some convergent boundaries ae a collision of oceanic crust subjecting underneath continental
crust. As a result, volcanic arches and oceanic trenches are formed. The Ring of Fires is a zone
marking major activity of frequent earthquake and volcanic eruptions between oceanic and
continental plates. The “Ring of Fire” is an arc stretching from New Zealand, along the eastern
edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and
South America. It is composed over 75% of the world’s active and dormant volcanoes.
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Earthquake Occurrences in Different
Tectonic Settings
Questions:
1. How can the location of earthquakes support the Theory of Plate Tectonics?
2. Which type of boundary generates the most intense earthquakes?
3. Even though the Ring of Fire and the Himalayas were formed from convergent
boundaries, how does the process in their formation differ?
4. How did the convergent plate boundary called the Ring of Fire get its name?
5. Why does oceanic crust subject or sink underneath the continental crust?
6. Draw a diagram to illustrate each of the 4 boundaries described in the reading.