Geoscience Reference
In-Depth Information
of fire breaks include unimproved roads and fields. Natural fire breaks can
include rivers, streams, and roads.
Public Outreach—
Encouraging
homeowners to develop a defensible space of
30 feet around their home, cleaning out gutters, using fire resistant shin-
gles and siding, and planting fire resistant trees and shrubs are all ways that
residents can protect their homes. Using residents as partners in your pre-
paredness and mitigation efforts is good business practice for Emergency
Management.
Earthquakes
Description and History
The Earth's crust is made up of many sections, called tectonic plates. These plates
are consistently in motion due to the convective currents of the Earth, which is
caused by the heating cycles in the planet's mantle (the liquid layer beneath the
Earth's crust). At the deepest parts of the mantle, the temperatures get extremely
hot due to the proximity to the Earth's core. As these parts of the mantle get hot,
they rise through the Earth's mantle, where they cool and begin to sink toward the
Earth's core again. This cycle causes convective currents. These currents are what
cause the tectonic plates to move.
There are three different types of movements that occur with tectonic plates.
The energy released as these plates move is what triggers earthquakes.
Divergent Plate Movement (or Divergent Fault Lines)—Any earthquake from
this type of movement occurs when tectonic plates separate and drift apart.
In most cases, magma will rise up and fill the void created by the separation.
In some cases, a plate may slide downward to fill the gap. These types of plate
movements typically occur in the ocean. One prime example of this type of
plate movement is the Mid-Atlantic Ridge in the Atlantic Ocean. This diver-
gent fault line reaches through Iceland, and is thought to eventually cause the
country to split into at least two pieces.
Convergent Plate Movement (or Convergent Fault Line)—An earthquake
occurring from this type of movement occurs when tectonic plates collide.
During such a collision, a subduction zone can form, where the older plate
begins to slide under a younger plate, forming a trench. These trenches can be
many miles wide. The best example of convergent plate movement is on the
Indonesian Island of Sumatra with the Great Sumatran fault. This fault last
caused a large earthquake in December 2004 and caused devastation along
its northern end.
Transforming Plate Movement (or Transform Fault Line)—An earthquake
occurs at one of these fault lines when energy is released from two tectonic
plates rubbing past one another. The San Andreas Fault in California is an
