EQ 2 Mitigation and Summary

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Geological Sciences
GEOL 2390
William M.Last

Earthquakes Continued... MITIGATION • lateral spread/flow failure: avoidance, zoning, excavation (if small) • général liquéfaction/bearing strength loss: engineering designs: ◦ drainage, grouting, artificial compaction, deep foundation ■ expensive!! ■ small area only Summary EQ Hazards Mitigation 1. community preparation/education 2. land use management 3. EG engineering/design -- retrofitting, reinforced concrete, etc. 4. EQ prediction/EQ control 1. Community Preparation • Mexico City 1985 : perception of EQ hazard very low: no preparation 2. Land use management • simplest, most direct way of reducing losses - simply don't live, build in eq prone ar- eas • options if aware of risk: ◦ refusal of rebuilding/renovation permits construction of critical structures ■ classic example: Bodega Bay Nuclear Plant 3. EQ Engineering/design • most deaths caused by collapse of man-made structure • technologically possible construct building to withstand operate-strong (6-7) eq but 50% more expensive ◦ result - most EQ prone areas under coded ◦ San Fernando 1971: 90% of buildings collapsed exceeded building code ◦ Caracas 1967: much new construction in previous 10 yr (i.e. modern build- ings) ■ most rigid code ater Calif ■ total collapse 5 high rise ■ major structural damage 500 other 30 story buildings ◦ biggest upgrading problem ■ 30% of population lives/works in high risk zone ■ $$$ • general: ◦ sufficient spacing ◦ no ornamentation ◦ rectangular vs. complex ◦ steel reinforced concrete 4. EQ Prediction/Control • only within past decade • last 5 years major advances but still elusive appraoaches 1. long-term analysis seismicity/recurrence rates • ID seismicity gaps ◦ plot historical seismic activity on spatial basis ◦ much used before 60s but with advent of plate tectonics ◦ two possibilities ◦ slow release of strain (creep) ◦ strain accumulating (release in major quake) • ◦ i.e. gap may be the most hazardous • • gaps: nothing about how large, how often statistical analysis of historical records: develop
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