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| Seismograph
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| Earthquake
Magnitude |
Moment
Magnitude is the measure of total energy released by an earthquake.
Moment
magnitude is the measurement and term generally preferred by scientists
and
seismologists to the Richter scale because it is more precise.
It is not based on instrumental recordings of an earth quake, but on
the area of
the fault that ruptured in the quake. It is calculated in part
by multiplying the area of the fault's rupture surface by the distance
the
earth moves along the fault.
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| Recent
Seismic Activity |
USGS
A map showing the recent earthquake activity worldwide
IRIS
Worldwide data with seismograms from the Wilbur II seismic stations.
CRSEIZE
Imaging the seismogenic zone along the Middle America Trench, Costa Rica
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Education
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Literature
& eBooks
Children's Classic Literature by Twain, Bronte, Fitzgerald, Hawthorne,
Thoreau and more.
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Earthquakes and Geology in Costa Rica
All
of us have felt the earthquakes that occur occasionally in Costa Rica.
Depending
on your level of understanding of the geologic processes which caused
these
earthquakes, you may have been a little frightened, or you may have
thought
it was a little fun and exciting. To a geologist, these little
earthquakes
are a good sign, Mother Earth letting go of her forces a little at a
time. § continued below
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| Costa Rica Geology |
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| Plate Tectonics |
The oceanic Cocos Plate and the continental Caribbean Plate are
converging
(moving toward each other) at the rate of about 80mm/year.
Continental
plates are made up of rock materials that are less dense (lighter) than
oceanic
plates. At the margin of the collision, the continent "floats" and the
oceanic
crust "sinks", causing a deep trench along the boundary, which is
slightly
offshore and parallel to our coast.
As the oceanic plate sinks (subducts), it continues to move inland deep
underground,
until it sinks deep enough to melt into magmas and lavas. The
string
of volcanoes trending through central Costa Rica are the heat and
pressure
relief valves of this melted oceanic rock. Between the offshore
trench
and the onshore volcanoes lies a zone of continental rocks sliding over
oceanic
rocks deep underground. This zone is not smooth, and the
roughness
of the zone causes large chunks of earth to collide, push against each
other,
and sometimes break. On the surface, we feel the tremors and vibrations
of
these many underground collisions as earthquakes. §
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| Homework
Help |
Global
Geology
earth science and expat homeschooling in Costa Rica.
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| Volcanoes
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Please, please remember that the Red Cross (Cruz Roja) is NOT a
government
organization. It depends on donations from the public and volunteers.
Their
services are among the most trusted on the planet, and many people
don't
even think about that until they are in desperate need of their help.
Donate
whatever and whenever you can!
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Predicting Large Earthquakes
The Nicoya Seismic Gap is an area which has not experienced a large
earthquake
in over 50 years. Large earthquakes, of magnitude 7 or higher,
have
occurred in this gap in 1853, 1900 and 1950. Scientists
from
all over the world have been studying the geology of this special area
for
years, and most are predicting that this area is well overdue for a
large
earthquake to relieve the stresses and strains of the earth that is
moving
beneath us. Marino Protti, Director of OVISCORI (Observatorio
Volcanológico
y Sismológico de Costa Rica) has stated that "the Nicoya gap
has the potential to generate an earthquake with moment magnitude above
7.5".
Magnitude
comparisons
are on a logarithmic scale, so a magnitude 6 earthquake would be 10
times
more destructive than a magnitude 5. Then a magnitude 7 would be
100
times more destructive, and a magnitude 8 would be 1000 times more
destructive.
So what has been predicted by OVISCORI, a 7.5, is the type of
earthquake
that leaves very few buildings standing and causes fissures in the
ground.
It would be something like the energy released by 100 hydrogen bombs,
or about 500 times more destructive than what we typically feel during
the recent !! §
| Costa Rica Geology |
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| Middle America Trench and the Nicoya
Seismic Zone |
An Early Warning System in Costa Rica
In the early to mid 1990's, the Ocean Drilling Program of Texas A&M
University
conducted an extensive study of the Middle American Trench, just
offshore
of the Nicoya Peninsula. Their findings spurred several other worldwide
agencies
to study the Nicoya Seismic Gap as a possible testing site for an
earthquake
early warning system. Over the last decade, OVSICORI,
together with
cooperating agencies from around the world, has implemented a system of
GPS
receivers to measure the earth's movement, and a system of seismic
receivers
to measure and record tremors and earthquakes on the Nicoya Peninsula.
Since radio waves travel faster than seismic waves, the theory behind
the
early warning system is that when a large earthquake occurs, radio
transmissions can give San Jose about 30 seconds of warning before the
earthquake waves demolish the city. San Jose is the major
metropolitan center, where the greatest loss of life and property
can be expected.
On the Nicoya Peninsula, however, there will be no prior warning.
The
Costa Rican government is also implementing an emergency response
procedure
to deal with the aftermath of large natural disasters, such as the
predicted
large earthquake. What can we do? Hope for more small earthquakes
on
the Nicoya peninsula, like the ones in January, to relieve the
underground
stresses that have been building up for years. §
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