ChiChi Earthquake, Taiwan, 21 September 1999

km/sec. Slip velocity less

Building Damage wrong design wrong construction wrong location engineer contractor geologist

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!

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

Geology & seismology Where are the faults? How often do they move? Liquefaction? Basin Resonance? Accelerations near fault? (Brune ripple) Focussing effects? (Heaton pulse) Important effects in the 1999 Chichi Earthquake

Lateral spreading Liquefaction in Wufeng

Liquefaction-induced sand-venting through lateral spreading fissures

Ground fissuring MSK VIII-IX Lateral spreading and Foundation settlement Channel fracturing & collapse

Accelerations near the surface rupture 2.5 km/sec Brune ripple

Toe collapse and hanging wall accelerations How fast did the fault slip near the surface? How did toe of thrust deform?

Footwall Hanging Wall Collapsed toe of thrust Masonry posts still standing =Intensity VII (<0.4 g) rolled but not thrown

Minor to moderate damage (MSKIntensity VIII)

Masonry wall collapse Masonry pillar “shaken not stirred!” Toe footwall MSK Intensity VIII

1 km

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

50-m-WIDE ZONE OF ROTATION & SHORTENING

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!

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)

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!