ChiChi%20Earthquake,%20Taiwan,%20%2021%20September%201999

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ChiChi Earthquake, Taiwan, 21 September 1999
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Propagation _at_3 km/sec. Slip velocity less
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Building Damage

• wrong design
• wrong construction
• wrong location

• engineer
• contractor
• geologist

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Wrong Engineering

• Ground floor too weak
• Building not symmetrical
• Too close to next building
• Foundations not deep enough
• Accelerations too large (inappropriate seismology
  and geology input)

Conclusion Taiwanese Engineering is
Exceptionally good. 95 success. Most
buildings held!
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Construction problems in concrete structures

• Weak cement (should be strong)
• Brittle steel (should be ductile)
• Insufficient stirrups in columns
• Wrong positioning of steel
• Weak wall/column bonding

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Geology seismology

• Where are the faults?
• How often do they move?
• Liquefaction?
• Basin Resonance?
• Accelerations near fault? (Brune ripple)
• Focussing effects? (Heaton pulse)

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Lateral spreading Liquefaction in Wufeng
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Liquefaction-induced sand-venting through lateral
spreading fissures
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Accelerations near the surface rupture
2.5 km/sec
Brune ripple
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Toe collapse and hanging wall accelerations
How fast did the fault slip near the surface? How
did toe of thrust deform?
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Minor to moderate damage (MSKIntensity VIII)
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VIII
VII
VIII
VII
VIII
VII
1 km
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Conclusions on thrust emplacement 1. Slip was
relatively slow (velocities 1-2 m/sec) 2.
Accelerations were less than 0.5 g on the toe of
the thrust Brune ripple apparently not
applicable to thrust faults in western Taiwan
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50-m-WIDE ZONE OF ROTATION SHORTENING
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Conclusions

• Structures must not be built on faults
• Width of zone damage zone 50 m on hanging wall
  near bedrock
• Width of severe damage 1 km in sediments

Observation Many schools and bridges built near
or across faults!
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recommendations

• Need better acceleration data from fault zones
  (make fault zones parks)
• Instrument and map thrust faults to north
• Need to ensure that contractors understand the
  need for tied stirrups, and correct density. in
  concrete columns.
• Need to avoid regions of known liquefaction (make
  fissured zones into parks)

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High tech. reccommendation

• Inexpensive accelerometers could be included in
  every new building in Taiwan as a Black Box
  recorder like those used in aircraft.
• Cost could be less than 100 given Taiwanese
  ingenuity and experience!
• This would make contractors realize that they
  will have to answer for bad construction
  practices!