Environmental Geology lecture outline - Earthquake engineering.
"A bad earthquake at once destroys our oldest associations: the earth, the very emblem of solidity, has moved beneath our feet like a thin crust over a fluid: one second of time has created in the mind a strange idea of insecurity, which hours of reflection would not have produced. .... it is a bitter and humiliating things to see works, which have cost man so much time and labour, overthrown in one moment. " Darwin 1845, on his experience of an earthquake in Concepcion, South America
Given difficulty or even inability to predict earthquakes an alternate approach is simply to learn to live with them. Most critical in such an approach is to build structures so that they can survive an earthquake.
Example of design criteria (the engineering goal):
Image showing sand that was liquefied during the Loma Prieta earthquake in California, and which 'boiled' up to the surface, demonstrating the ability of wet sediment to be mobilized during an earthquake. From USGS site: http://gallery.usgs.gov/photos/mQHs38Vjj1_82
Aerial view of Van Norman dam, which has internal liquefaction aiding mass wasting, and near dam failure during 1971 San Fernando earthquake. Many people down stream were evacuated. Photo from USGS website: http://pubs.usgs.gov/gip/earthq4/severitygip.html
Diagram showing the different ground movement responses to the Loma Prieta Earthquake of 3 stations close to each other. The amplitude of the seismic trace is a function of the earthquake size, of the distance from the earthquake center, and of the type of substrate. In these responses the earthquake size is constant (since all traces are for the same earthquake, and the distance from the earthquake center is not greatly different. Most of the difference is because of the substrate. Water and clay rich sediments can amplify siesmic waves tenfold or more. Image from USGS site: http://earthquake.usgs.gov/regional/nca/qmap/
USGS map showing liquefaction potential for part of Oakland from a 7.1 earthquake on the Hayward fault, part of the San Andreas plate boundary. Map from USGS site: http://pubs.usgs.gov/fs/2003/fs028-03/
Importance of building material and flexibility, and the concept of cyclic loading.
Importance of building shape:
Severe damage from the Mexico City earthquake in 1985. Photo courtesy of USGS: http://libraryphoto.cr.usgs.gov/cgi-bin/show_picture.cgi?ID=ID.%20Celebi,%20M.%2040ct
Approaches in increasing safety of building:
Types of building failure typical during an earthquake:
The response can be very complex and is due to materials used, design elements and shapes.
Collapse of Oakland freeway during Loma Prieta earthquake resulting in loss of life (41 lives). Note how columns failed allowing the top tier to collapse on to the lower tier. The reinforcing internal rods were inadequate and base column shear occurred as part of the response. Image from USGS site: http://earthquake.usgs.gov/earthquakes/states/events/1989_10_18.php
Damage to a column (buckling) during the 1994 Northridge earthquake in California that caused over $2 billion worth of damage. Note the strong vertical reinforcement, but minimal orizontal reinforcement. Image source and more information at USGS site - http://pubs.usgs.gov/of/1996/ofr-96-0263/execsum.htm
Another structure damaged during the Northridge earthquake. The failure was asmmetric here, as the interior was weaker than the exterior walls, leading to inward collapse. Image source and more information at : http://pubs.usgs.gov/of/1996/ofr-96-0263/execsum.htm
The San Francisco Courth House was retrofitted with a base isolation system to reduce building shaking from earthquake waves. The basic idea is of decoupling the building and the ground so that during the earthquake the ground can move independently of the building. Images from USGS website: http://pubs.usgs.gov/fs/2005/3052/
What to do for domestic abodes?
For large pipelines 2 approaches are: a) shutoff valves connected to accelerometers, b) flexible sections pipeline crosses fault.
Picture of where the Alaska oil pipeline crosses the Denali fault, and where the fault ruptured and moved in 2002 during an earthquake, but the pipeline survived. More details and image sources at the USGS site - http://pubs.usgs.gov/fs/2003/fs014-03/pipeline.html .
Cost? 5% of original without, 50-100% as retrofit.
Critical facilities (some review)?
Legal codification of earthquake engineering?
In class seismic hazard assessment exercise:
Split up, self-organize into groups of 4 to 5 people to complete the exercise. Each group will be given a section of Omaha to cover
The scenario is a Richter magnitude 6.8 has occurred just S of Omaha. Remember that such an occurrence is unlikely, although not impossible.
Consider the assigned area and think of the following questions for 5-10 minutes or so:
Write out a list of conclusions on the sheet provided, and pick a spokesperson to present them.
Try to be realistic, and not over dramatize. The idea is to scientifically evaluate to the best of your ability given what you have learned so far.
Areas to consider:
H.D. Maher Jr., 3/9/98
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