Download What is an earthquake?

yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

2009–18 Oklahoma earthquake swarms wikipedia, lookup

Reflection seismology wikipedia, lookup

Earthquake prediction wikipedia, lookup

Earthscope wikipedia, lookup

Seismic retrofit wikipedia, lookup

1880 Luzon earthquakes wikipedia, lookup

Earthquake wikipedia, lookup

Surface wave inversion wikipedia, lookup

Seismometer wikipedia, lookup

Earthquake casualty estimation wikipedia, lookup

Chapter 16
What is an earthquake?
• Shaking of the ground caused by
the sudden release of energy
stored in the rocks.
• When rocks are stressed, potential
energy is stored in them.
• Rocks can behave plastically upto
a certain limit (elastic limit), after
which they fail and release the
• Energy waves produced by an
earthquake are called Seismic
• The generation of an earthquake is
explained by Elastic Rebound Theory.
• According to this theory, the sudden
release of progressively stored strain in
rocks causes movement along a fault
and an earthquake is generated.
Causes of earthquakes
Movement along a fault
Volcanic eruptions
Plate movement
Earthquake terminology
• Focus: the point inside the earth
where seismic waves first
• Epicenter: the point on ground
surface directly above the focus. It
may be any geographic locality.
Seismic waves
• 2 types
–Body waves: traveling inside the
–Surface waves: travel on the
earth’s surface.
• Body waves:
–P-waves (primary)
–S-waves (secondary)
• P-wave: is the fastest (4-7 km/sec)
and is the first to arrive at a
recording station.
• P-wave: compressional or
longitudinal wave in which rocks
vibrate back and forth parallel to
the direction of wave propagation.
• S-wave: slower (2-5 km/sec) and
arrives after the P-wave at a
recording station.
• It’s a transverse wave in which the
rock vibrates perpendicular to the
direction of wave propagation.
• Surface waves:
–slowest waves generated by an
–They take longer to pass and
cause more property damage.
EQ measurement
• The instrument used to measure
an EQ is called a seismometer.
• Seismograph: paper or electronic record of
an EQ.
World seismograph stations
Locating EQ Epicenter
• Travel time of the seismic waves
from the focus to the seismograph
station is used to determine the EQ
• P and S waves gradually separate
because they travel at different
• The P-S interval is compared with a
standard travel-time curve.
• Data from one station can be used
to determine only distance to the
station and not the direction.
• At least three stations are required
to determine the location of the
Measuring the size of an EQ
• Two ways of determining the EQ
Measuring the size of an EQ
• EQ Intensity: it is a measure of
how an area has been damaged by
the EQ.
• Modified Mercalli Scale is used to
measure intensity.
• EQ magnitude: it’s a measure of
the amount of energy released by
an EQ.
• EQ magnitude is reported on the
Richter scale.
• It is done by measuring the height
(amplitude) of a specific wave.
• ML = log10A(mm) + (Distance
correction factor)
Magnitude (log Scale)
Possible Effects
Normally only detected by instruments
Only faintly felt
Faint tremor causing little damage
Structural damage
Distinct shaking, less well-constructed
buildings collapse
Most buildings destroyed
Major structures destroyed
Ground seems to shake-catastrophic
Effects of EQ
• Primary effects: occur immediately
from ground shaking
• Secondary effects: damage caused
Effects of EQ
–Liquefaction: wet, saturated soil
changes from solid to liquid as a
result of shaking.
Global distribution of EQ
• 3 belts;
–Circum-Pacific belt
–Mediterranean-Himalayan belt
–Continental interior
Mitigating EQ effects
Avoiding EQ prone zones
Foundation design
Structural modifications
Building codes
Predicting EQ
• Rock monitoring: rock properties
begin to change before its failure.
• Water levels: increase or decrease.
• Radon emission: increases before
an EQ.
Predicting EQ
• Seismic gap: regular pattern of EQ
• Animal behavior: snakes, dogs.
Assignment 2
Rivers, groundwater, lakes
Ohio EPA
Great lakes, lake erie
Relative proportions
Maximum Contaminant Level
Primary contaminants