Please help with this as I can not understand it at all. Imagine you've been shown a seismogram from an earthquake on which you can see the first arrival of P waves, followed some time later by the first arrival of S waves. You work out that the S wave arrived 5 minutes after the first P wave. Use this information to estimate the epicentral angle, explaining how you arrived at your answer

Question

Please help with this as I can not understand it at all. Imagine you've been shown a seismogram from an earthquake on which you can see the first arrival of P waves, followed some time later by the first arrival of S waves. You work out that the S wave arrived 5 minutes after the first P wave. Use this information to estimate the epicentral angle, explaining how you arrived at your answer

Answer 1

To estimate the epicentral angle, we need to understand the relationship between the arrival times of P waves and S waves and their respective distances from the earthquake epicenter.

Here's how you can arrive at the answer:

1. Understand the basics: P waves are faster and arrive before S waves. The time difference between their arrivals is related to the distance from the earthquake epicenter.

2. Consult the seismic wave travel time curve or chart: This chart shows the relationship between the distance from the earthquake epicenter and the time interval between the arrival of P and S waves. You can find these charts in seismology textbooks or online resources.

3. Use the given information: In this case, we know that the S wave arrived 5 minutes after the first P wave. Note this time difference, as it will be crucial for estimating the epicentral angle.

4. Estimate the distance: Determine the distance from the seismograph station or location where the earthquake was recorded to the earthquake epicenter. This can be done by referring to the travel time curve chart for the known time difference.

5. Find the corresponding epicentral angle: Once you have the estimated distance, refer to a seismic wave travel time curve or chart that also provides the relationship between the distance and the epicentral angle. Use this chart to find the approximate epicentral angle based on the estimated distance.

6. Note any limitations: Remember that this is an estimation, and other factors like the velocity of seismic waves in different layers of the Earth's interior may affect the accuracy. The estimation assumes a simplified Earth model.

By following these steps and using seismic wave travel time charts, you can estimate the epicentral angle based on the time difference between the arrivals of P and S waves.

Answer 2

This answer isn't really helpful. Can somebody give a general explanation as to how you can work out the epicentral angle? I've got the same question and have been provided with a graph of p wave and s wave travel time. I'm assuming you find the place on the graph where the difference between the s and p waves is 5 mins, but do you measure the epicentral angle from the p wave curve or the s wave curve?

Answer 3

Ignore what I just said!! The answer just popped into my head after about half an hour of staring blankly at my book. (I'm assuming this is OU S105) I think what you have to do is find the point where the S wave and P wave are 5 mins apart (you should be able to measure what 5 mins equals in mm from the y axis of the graph you've been given). Read the graph down between the two points on the S and P curves to read the epicentral angle.