Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out

Earth_Layered_Structure

VIEWS: 7 PAGES: 15

									Earth’s Layered Structure

  And Predicting Earthquakes
    Predicting Earthquakes
Can Earthquakes be predicted?
Short range predictions:
The goal is to provide info on location and
magnitude of a large earthquake
Scientists monitor; uplift, water levels,
pressures in wells and radon gas
emissions
So far, it has not been successful
      Long-term Predictions
Long range forecasts give the probability of a
certain magnitude earthquake occurring within
30 to 100 years
This data is used for updating building codes
Based on the idea that earthquakes are
repetitive
Scientists study historical record of quakes and
the seismic gap
Seismic gap is an area along a fault were there
has not been earthquake activity for a long time
Currently not able to make accurate predictions
  Earth’s Layered Structure
Composed of 3 major
zones defined by
chemical composition
Crust
Mantle
Core
                Crust
Thin rocky outer layer
Oceanic crust: ~7 Km thick, mostly basalt
and gabbro, density ~ 3.0 g/cm, younger
than 180 million years
Continental crust: 8-75 Km thick, average
of 40 Km, granitic rocks, density ~ 2.7
g/cm, some parts older than 4 billion years
Mmmm crust
               Mantle
Over 82% of Earth’s volume is contained
here
Rocky shell that extends to a depth of
2890 Km
Dominant mineral in upper mantle is
peridotite with a density of 3.4 g/cm
                  Core
Composed of Iron-Nickel alloy
At the center of the core the density is
almost 13 g/cm
Divided into inner and outer core
   Layers Defined by Physical
           Properties
Lithosphere: the crust and upper most
mantle, relatively ridged layer ~100 Km
thick
Asthenosphere: weak layer beneath the
lithosphere, pressure and temp lead to
small amount of melting, rocks easily
deformed
Layers by Physical Properties cont.
 Lower mantle: 2230 Km thick, more
 ridged than the upper mantle, due to high
 temps rocks are still capable of gradual
 flow
 Outer core: liquid, 2260 Km thick, flow of
 melted iron creates Earth’s magnetic field
 Inner core: 1220 Km radius, higher
 temperature and pressure than outer core,
 high pressure causes inner core to be
 solid
 Discovering Earth’s Layers
In 1909 a Croatian seismologist, Andrija
Mohorovicic, presented evidence for
layering
Discovered seismic waves travel much
faster once they reach a point of 50 Km in
depth
This is the boundary between the crust
and mantle
Known as the Mohorovicic discontinuity
Shortened to Moho.
Andrija Mohorovicic
      Other discontinuities
Between mantle and outer core was
discovered by observing P waves being
bent around the outer core
S waves couldn’t travel through outer core,
this told scientists it is liquid
Evidence of Earth’s composition
 Based on seismic data and drilling
 Other evidence from meteorites: scientists
 believe meteorites are made from the
 same material Earth is made of.
 Meteorites can be stony (like Earth’s crust)
 or Iron and Nickel rich (like Earth’s core?)

								
To top