GEOL 106 - LEC 12

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Geological Sciences and Geological Engineering
GEOL 106

Hazard City • Map reading exercise o Introduction o Basic map reading o Reading topographic maps o Plateu map o (nothing needs to be handed in) Hazard city • Be on earthquakes Carbon-14 Dating • So once the tree dies the amount of c14 in the tree decreases at a fixed rate o We measure the 14c/12c ration • Half-life – length of time for ½ of the radioactive element to decay • Carbon 14 starts to decade into 14n o Half lives … when at 0 no 14 .. 1 half and half … 2 more 14n .. 3 more 14 n less c14 o 1 half life for c14 = 5730 years o Note yr BP – means years before present o 14c dating ( and other radiometric “dating” methods) o can be used to determine when a fault last moved (if your seismometers haven’t already told you the answer) o is it active? o But .. it is a “subjective: determination to decide if a particular movement event was a “big” earthquake or just a small one o We can turn to other evidence of “big” quake activity that is less subjective NOW – after all of what we talked about, you can then create a full picture of the seismic risk for your area of interest • Write reports • Try to quantify it • Make risk maps Genral approach to risk analysis and risk management • Risk Analysis o 1. Understand the hazard(general) o 2. Determine the risk from the hazard for the region of interest (risk = phxsh) • Risk Management o 3. Determine ways to reduce ph and/or sh o 4. Do a “cost”-benefit analysis  determines what you can “afford” to do o 5. Implement mitigation techniques if warranted 3. determine ways to reduce ph and /or sh • 1. Apply land-use planning and zoning (reduce sh “) o a) use high – risk areas for low population use (eg. Parks;golf courses) o b) in oarticular don’t build in areas of soft soil or soils that might liquefy • 2. Apply stringent building codes(“) o a)choose appropriate building materials  good materials – wood, steel, reinforced concrete (all flexible which is good)  bad materials – heavy masonry, stucco, adobe, unreinforced concrete ( bad materials are un flexible and rigid)  ex. Earthquakes in 1988/1989 6.5-7 magnitude  loma prieta California (65 dead )good materials  Armenia 50,000dead (bad materials) o b) choose resistant building design  Examples, the worst damage occurs when the period of vibration. Of the ground and the building are the same  Ground periods – soft soil: several seconds.. solid rock :1 second  Building periods – Tail Blog : several seconds … Short blog: 1 second  Buildings have a natural period of vibration of N/10 seconds … N=number of stories  Example : the affect of building shape  Example of structural design: how to build a house to resist seismic waves: Bolt It. Bracket It. Brace It. Block It. Panel It. o c) legislate construction regulations  This ensures that builders actually do a) and
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