GLG110 Geologic Disasters and the Environment

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GLG110 Geologic Disasters and the Environment
Today Chapter 5 Earthquakes, Contd
Instructor Professor Ramon Arrowsmith Email
ramon.arrowsmith_at_asu.edu Office PSF-640
480-965-3541
TA Tom Foltz Email Thomas.foltz_at_asu.edu Office
PSH-574
Course Website http//glg110.asu.edu
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Business of the Day

• Homework review
• Turn it in!
• http//quake.usgs.gov/kap/carrizo/
• Overheads and discussion
• Exam 1 review
• http//glg110.asu.edu/Exams/GLG110Exam1Review.html
  

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Todays earthquake topics

• Earthquake recurrence--homework
• Earthquake locations
• Earthquake hazards
• Earthquake risk and earthquake prediction
• Earthquake magnitudes and frequency

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Seismic waves and Earthquake locations
Seismic waves P waves (compressional and
faster) S waves (shearing, slower, and dont
travel through fluids) Surface waves (move along
earths surface, have complex motion, and cause
most damage)
Keller, 2002
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Northridge earthquake seismograms
Keller, 2002
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Earthquake location using P-S wave delay times
Can be done by computer rapidly with higher
precision due to multiple stations and some
knowledge of wave speed distribution in rocks.
Keller, 2002
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Lets look at the distribution of recent
earthquakes and their magnitudes
http//earthquake.usgs.gov/recenteqs/
http//wwwneic.cr.usgs.gov/neis/bulletin/bulletin.
html
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Earthquake Hazards Material amplification
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Earthquake hazards Mexico City 1985 earthquake
On the morning of September 19, 1985, 717 AM, a
very disastrous earthquake hit Mexico City. This
earthquake had the magnitude of 8.1. More than
100 buildings collapsed and over a 100,000
housing units were destroyed. It caused 4
billion in damage. It was so powerful, the shake
of the ground had shook tall buildings in Texas.
The earthquake had only lasted for about 3
minutes. This surprised many residents of Mexico
City because they couldn't believe that so much
damage could happen in only 3 minutes. This
earthquake had killed 20,000 people, injured over
40,000 people, and left 50,000 to 90,000
homeless. Fortunately, since the earthquake had
occurred so early in the morning, many people
were not at school or work yet.
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This residential and commercial building sank
more than three feet into the partially liquefied
soil. Photo credit Reinsurance Company, Munich
Germany. (http//www.geo.arizona.edu/K-12/azpepp/e
ducation/history/mexico/sphotos/dm2.html)
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Collapsed Floors Punctured by Load-Bearing
Column Severe resonance oscillations of the
buildings caused strain at the juncture between
columns and ceiling slabs. The vertical coluns
were punched through the heavy floors that
collapsed around them. Photograph credit
Reinsurance Company, Munich, Germany.
http//www.geo.arizona.edu/K-12/azpepp/education/
history/mexico/sphotos/dm4.html
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Generalized geologic map of Mexico city showing
ancient lake deposits where greatest damage
occurred.
Keller, 2002
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Plate tectonic setting for 1985 Mexico City
Earthquake Ocean-continent subduction
Keller, 2002
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Earthquake risk and earthquake prediction
Probabilistic, long term
Keller, 2002
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Earthquake risk and earthquake prediction Short
term

• Foreshocks
• Preseismic tilting
• Seismic gaps
• Anomalous animal behaviour?
• Electromagnetic signals

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Sequence of Earthquakes in Turkey in 20th
century can one earthquake set up another?
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Global
http//neic.usgs.gov/neis/eqlists/eqstats.html
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Earthquake occurrence
Lose them at the top because they are too small

• Inverse
• magnitude-
• frequency
• relationship

EQs
Magnitudes
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http//neic.usgs.gov/neis/eqlists/eqstats.html
On average, same number of big quakes more small
ones with better seismic networks.
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http//neic.usgs.gov/neis/eqlists/eqstats.html