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USA Today reported that Parkfield, California, is dubbed the world's earthquake capital because it sits on top of the notorious San Andreas fault. Since \(1857,\) Parkfield has had a major earthquake on the average of once every 22 years. (a) Explain why a Poisson probability distribution would be a good choice for \(r=\) number of earthquakes in a given time interval. (b) Compute the probability of at least one major earthquake in the next 22 years. Round \(\lambda\) to the nearest hundredth, and use a calculator. (c) Compute the probability that there will be no major earthquake in the next 22 years. Round \(\lambda\) to the nearest hundredth, and use a calculator. (d) Compute the probability of at least one major earthquake in the next 50 years. Round \(\lambda\) to the nearest hundredth, and use a calculator. (e) Compute the probability of no major earthquakes in the next 50 years. Round \(\lambda\) to the nearest hundredth, and use a calculator.

Short Answer

Expert verified
(a) Poisson distribution is suitable due to random, independent events. (b) At least one earthquake in 22 years: ~0.63. (c) No earthquake in 22 years: ~0.37. (d) At least one earthquake in 50 years: ~0.90. (e) No earthquakes in 50 years: ~0.10.

Step by step solution

01

Justification for Poisson Distribution

A Poisson distribution is suitable for modeling the number of rare events within a fixed interval of time or space, such as earthquakes in Parkfield, because it is based on events that occur independently. Since earthquakes occur randomly and independently, with a fixed average rate known over the years (mean rate is once every 22 years), it fits the Poisson model well.
02

Define Average Rate and Compute for 22 Years (Part b)

Given the average occurrence rate of 1 major earthquake every 22 years, we define the parameter \(\lambda\) as \(1\) for a 22-year period. To find the probability of at least one major earthquake in 22 years, use the formula for complement: \(P(r \geq 1) = 1 - P(r = 0)\), where \(P(r = 0) = \frac{\lambda^0 e^{-\lambda}}{0!} = e^{-1}\).
03

Compute Probability for At Least One Earthquake in 22 Years

Substitute \(\lambda = 1\) into the formula: \[P(r \geq 1) = 1 - e^{-1} \approx 1 - 0.3679 = 0.6321\] Thus, the probability is approximately \(0.63\).
04

Compute Probability for No Earthquake in 22 Years (Part c)

With \(\lambda = 1\) for 22 years, compute the probability of no earthquakes using: \[P(r = 0) = e^{-1} \approx 0.3679\] Thus, the probability of no earthquakes is approximately \(0.37\).
05

Define Average Rate for 50 Years and Compute (Part d)

For a 50-year period, \(\lambda\) is calculated as:\[\lambda = \frac{50}{22} \approx 2.27 \]The probability of at least one major earthquake in 50 years is found by: \(P(r \geq 1) = 1 - P(r = 0)\).
06

Compute Probability for At Least One Earthquake in 50 Years

Substitute \(\lambda = 2.27\) into the formula: \[P(r \geq 1) = 1 - e^{-2.27} \approx 1 - 0.103 = 0.897\] Thus, the probability is approximately \(0.90\).
07

Compute Probability for No Earthquake in 50 Years (Part e)

With \(\lambda = 2.27\) for 50 years, compute the probability of no earthquakes using: \[P(r = 0) = e^{-2.27} \approx 0.103\] Thus, the probability of no earthquakes is approximately \(0.10\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Earthquake Probability
When we talk about earthquake probability in Parkfield, California, we are trying to predict how likely it is for an earthquake to occur within a certain time frame. This involves understanding factors such as historical patterns and geological conditions. Since Parkfield sits on the San Andreas fault, it experiences earthquakes regularly. By analyzing the frequency of these events, we can estimate future occurrences.
The Poisson distribution is particularly useful in this case because it allows us to model the probability of a given number of earthquakes over a fixed time interval. Earthquakes in Parkfield have occurred on average every 22 years, and the distribution helps capture the random nature of these occurrences.
For example, to find the probability of at least one earthquake in the next 22 years, we use the Poisson probability of zero earthquakes occurring and subtract it from one. This calculation uses the parameter \(\lambda\) which, in this context, represents the average number of earthquakes expected during the time period. By doing so, we harness the power of statistical tools to make informed predictions.
Mathematical Modeling
Mathematical modeling is a vital tool used to understand real-world phenomena by representing them with mathematical concepts and equations. In the case of Parkfield's earthquake probabilities, we use the Poisson distribution to create a model of possible earthquake occurrences.
The equations used here are not just numbers on paper; they help us visualize and analyze events' likelihood, severity, and timing. In modeling earthquakes, we assume that events happen independently and follow a constant average rate, making the Poisson distribution a good fit. This model starts with defining the correct \(\lambda\). For a 22-year period, \(\lambda = 1\) since one earthquake is expected, whereas for a 50-year period, we calculate it based on the proportion of past data, resulting in \(\lambda \approx 2.27\).
The Poisson probability mass function gives us probabilities for different numbers of earthquakes occurring and enables scientific decision-making about earthquake preparedness. Mathematical modeling, hence, transforms complex empirical observations into comprehensible insights that communities and scientists can use to predict and prepare.
Statistical Analysis
In statistical analysis, we use data to draw conclusions and make decisions based on evidence. With earthquake predictions, we rely on statistical methods to understand the likelihood of seismic events. The Poisson distribution is a cornerstone of this analysis when dealing with rare events like earthquakes.
First, it's crucial to ensure our model accurately represents the situation. By validating historical data - like Parkfield’s 22-year average for an earthquake - we ascertain that the Poisson distribution suits our analysis. With the parameter \(\lambda\) set, we calculate precise probabilities. For instance, using \(\lambda = 2.27\) for 50 years, it allows us to find that the probability of at least one earthquake is roughly \(0.90\), while the probability of no earthquakes is about \(0.10\).
Such analysis assists authorities in planning infrastructure, emergency routes, and safety drills. It transforms abstract probabilities into actionable strategies. Statistical analysis does not only help understand past events but also prepares us for potential future scenarios, safeguarding lives and minimizing risk.

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