Lecture 10A / Earthquakes
Download
Report
Transcript Lecture 10A / Earthquakes
Earthquakes
GLG 101 - Physical Geology
Bob Leighty
These notes and web links are your primary “lecture” content in this class.
Additionally, various articles are assigned each week to supplement this “lecture”
information. I believe you’ll have enough information to reference without having
to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes.
You’ll find they are loaded with imagery and streamlined text that highlight the
most essential terms and concepts. The notes provide a framework for learning
and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have
included numerous hyperlinks to external web sites (like the Wikipedia, USGS,
NASA, etc.). Follow the links and scan them for relevant info. The information
from linked web sites is meant to supplement and reinforce the lecture notes –
you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content
more independently than in a traditional class. As always, I will help guide you
through this learning adventure. Remember, email Dr. Bob if you have any
questions about today’s lecture ([email protected]).
Leave no questions behind!
Explore and have fun!
Earthquakes
What’s Shakin’?
National Earthquake Information Center (NEIC)
World seismicity 1990-2000
Earthquakes
Earthquakes: why do we care?
Destructive (in lives & property)
Mexico City (1985)
Earthquakes
Earthquakes: why do we care?
Some types of building sites are better than others
> Bedrock is better than soft sediment
Earthquakes
Earthquakes: why do we care?
We can learn about the Earth's interior & tectonic plates
Earthquakes
What is an earthquake?
Elastic rebound theory - Stress builds up until rocks
deform elastically and then break, releasing energy
Quake = A sudden release of stored energy causing
vibrations (seismic waves) in rock
The size of a quake the amount of built-up stress
Earthquakes
Where do earthquakes occur?
Originate within the brittle part of the lithosphere
Mostly occur at plate boundaries (~95%)
Earthquakes
Where do earthquakes occur?
Focus - The actual location within the Earth where the
earthquake originates
Epicenter - The point on the Earth's surface above the focus
Earthquakes
Seismic Waves
Body Waves
P-waves
P-wave = primary wave or compressional wave
Fastest (4 to 7 km/sec)
Can move through solids & liquids
Earthquakes
Seismic Waves
Body Waves
S-waves
S-wave = secondary wave or shear wave
Slower (2 to 5 km/sec)
Can move only through solids
Earthquakes
Locating Earthquakes
Seismometer - Detects and records vibrations (earthquakes,
nuclear blasts, etc.)
Earthquakes
Locating Earthquakes
Seismogram - Record of vibrations (paper, electronic)
Earthquakes
Locating Earthquakes
surface
P
lag time
S
Earthquakes
Locating Earthquakes
To get the distance to an earthquake epicenter, we need:
1) the difference in arrival times (lag time) between P & S waves
2) data from 3 different seismic stations
Earthquakes
Earthquake Intensity
Magnitude
Richter Scale = measures earthquake intensity (energy) from
ground shaking
Determined by measuring amplitude (height) of the S-wave on
seismogram
Richter scale is logarithmic (each interval x10)
Seismic Moment Scale - A better estimate of earthquake energy,
now the standard
Earthquakes
Controls on Earthquake Damage
Distance from focus / depth of earthquake
Soft sediment vs. dense bedrock
Duration of earthquake
Population density
Building design and construction
Earthquakes
Destructive Effects
Ground Rupture
Earthquakes
Destructive Effects
Ground Rupture
Earthquakes
Destructive Effects
Liquefaction
Liquifaction - Soft sediment can amplify vibrations (watersaturated sediment can liquefy & turn to goop)
Earthquakes
Destructive Effects
Fire
Broken gas lines, water pipes, etc.
ex - San Francisco, CA (1906):
90% of EQ damage caused by fire
ex - Yokohama, Japan (1923):
576,262 houses burned,
143,000 people killed
Earthquakes
Destructive Effects
Tsunami
Tsunami - Caused by the sudden displacement of water
NOT a tidal wave
Earthquakes
Destructive Effects
Tsunami
Fast, but low in open ocean
Big & bad near shore (average up to 30 m high)
Earthquakes
Destructive Effects
Tsunami
Earthquakes
Destructive Effects
Tsunami
http://www.ess.washington.edu/tsunami/index.html
http://www.volcanolive.com/tsunami10.html
http://serc.carleton.edu/NAGTWorkshops/visualization/collections/tsunami.html
Earthquakes
Destructive Effects
Tsunami
Earthquakes
WWW Links in this Lecture
> NEIC - http://earthquake.usgs.gov/regional/neic/
> Tectonic plates - http://en.wikipedia.org/wiki/Tectonic_plates
> Elastic Rebound Theory - http://en.wikipedia.org/wiki/Elastic_rebound_theory
> Earthquake - http://en.wikipedia.org/wiki/Earthquake
> Lithosphere - http://en.wikipedia.org/wiki/Lithosphere
> Epicenter - http://en.wikipedia.org/wiki/Epicenter
> Seismic waves - http://en.wikipedia.org/wiki/Seismic_wave
> P-wave - http://en.wikipedia.org/wiki/P_wave
> S-wave - http://en.wikipedia.org/wiki/S_wave
> Seismometer - http://en.wikipedia.org/wiki/Seismometer
> Seismogram - http://en.wikipedia.org/wiki/Seismogram
> Richter Scale - http://en.wikipedia.org/wiki/Richter_magnitude_scale
> Liquifaction - http://en.wikipedia.org/wiki/Earthquake_liquefaction
> Tsunami - http://en.wikipedia.org/wiki/Tsunami
> http://www.ess.washington.edu/tsunami/index.html
> http://www.volcanolive.com/tsunami10.html
> http://serc.carleton.edu/NAGTWorkshops/visualization/collections/tsunami.html