Global Biogeochemical Cycles4.docx

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Boston College
Earth & Environmental Sciences
EESC 1158
Donald James

Geoscience Part 3 Notes Probability and Statistics in Science and Public Policy Decisions - How do scientists and public policy makers use the concepts of probability and statistics in the decision making process? Earthquake Probabilities • Uniform California Earthquake Rupture Forecast (UCERF) – the first comprehensive framework for comparing earthquake likelihoods throughout all of California Probability of an Earthquake - What does it mean when a scientist says that, over some period of time, there is a 50% probability that a large earthquake will occur in a given area? - Probability: a measure of the likelihood that an event will occur  Is a number expressing the likelihood that a specific event will occur, expressed as the ratio of the number of actual occurrences to the number of possible occurrences - Associate a number between 0 and 1 with the probability that an event will occur - Number of actual occurrences/Number of possibility occurrences - P=0: Impossible for event to occur (rolling a 7 on single die) - P=1: Certain that the event will occur - P=0.5: Just as likely that it will occur as that it won’t occur - P-0.9999: Extremely likely (but not certain) that the event will occur Simple Example of Probability and Statistics of Small Number of Observations and Public Policy Decisions - Challenging problem in earthquake prediction is that we are often dealing with situations in which we have: o Avery short period of time over which we have observations, and we are trying to understand an Earth process that occurs over very long periods of time (millions of years) - Ex. Suppose that a critical fatality is being built, and is expected to operate for 60 years (site for disposing radioactive nuclear waste) - You are hired as a consultant for environmental activist group to evaluate whether or not a damaging quake is likely to occur near the nuclear waste facility o Problem – What do we do with spent nuclear fuel and high-level radioactive waste? o Solution – Put it in Nevada??  Yucca Mountain, Nevada – Proposed site for the nation’s first long- term geologic repository for spent nuclear fuel and high level radioactive waste  Half life of nuclear wastes: 10’s to 100’s of thousands of years, remains at hazardous levels for millions of years 1978: Us Department of Energy began studying Yucca Mountain – is it suitable for the nation’s waste? - These wastes are a result of a nuclear power generation and national defense programs - Currently: these radioactive waste products are stored at 131 sites around the nation - 2010 – ObamaAdmin.Arguing that the Yucca Mountain solution wasn’t going to work, cancelled the construction Ex. Suppose that there is an actual (but unknown) 50% probability that over a 60-year period of time, at least one damaging quake will occur in the study area - You only have 300 years of data o Divide the 300 year time period into five 60-year periods, and check to see whether there was or wasn’t at least one damaging quake in the are during each 60 year period o Can model this by flipping a coin  In the four cases, the seismologist would estimate that the true probability is between 40%-60%, not bad considering real probability is 50%  But in one case, the seismologist would estimate the true probability is only 2-%, and in another case the estimate would be 80%  So our seismologist might suggest that the area is much more active, or much less active  There is one case of an earthquake that occurred in another 60 year period that has one ambiguous report of damage, ambiguities are very subtle, if you add in that one quake you can raise your estimate of the probability to 40% Earthquake Prediction: The 1975 Haicheng, China Earthquake “Successful” prediction; claimed that… - Chinese officials concluded that there was sufficient evidence to issue an earthquake prediction on February 4, 1975 for a quake that would occur near the city of Haicheng - Magnitude 7.3, widespread damage and 1,328 people were killed Tectonic Setting of the Earthquake - Did not occur along a well defined plate boundary - Intraplate earthquake Failures of prediction in China - July 27, 1976 in Tangshan - No forewarning, 200,000 deaths, significant damage throughout the city and in surrounding areas - Magnitude 7.2 March 22, 1966 Xingtai - Premier Zhou En-lai (leader of Chinese communist party) had been told of stories reported by survivors regarding “precursors” to the Xingtai earthquake including: o Foreshocks o Fluctuations in ground water levels o Changes in animal behavior
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