How seismologist can determine the difference in the arrival times between the P wave and S wave?
S waves are slower than P waves by a known amount. Therefore, the farther a seismic recording station is from the earthquake epicenter the greater will be the difference in time of arrival between the P and S wave.
What is the difference between the arrival time of P and S waves?
The different waves each travel at different speeds and therefore arrive at a seismic station at different times. P waves travel the fastest, so they arrive first. S waves, which travel at about half the speed of P waves, arrive later.
Why do P and S waves arrive at different times?
The direct P wave arrives first because its path is through the higher speed, dense rocks deeper in the earth. The PP (one bounce) and PPP (two bounces) waves travel more slowly than the direct P because they pass through shallower, lower velocity rocks. The different S waves arrive after the P waves.
How do you identify P and S waves on a seismograph?
The P wave will be the first wiggle that is bigger than the rest of the little ones (the microseisms). Because P waves are the fastest seismic waves, they will usually be the first ones that your seismograph records. The next set of seismic waves on your seismogram will be the S waves.
How do you identify S waves?
S wave (“direct” S arrival) is identified by approximate time position in the seismogram, large relative amplitude, and lower frequency than the preceding P arrivals.
How do you find S and P waves?
Measure the distance between the first P wave and the first S wave. In this case, the first P and S waves are 24 seconds apart. Find the point for 24 seconds on the left side of the chart below and mark that point. According to the chart, this earthquake’s epicenter was 215 kilometers away.
How fast do P waves travel?
Typical values for P wave velocity in earthquakes are in the range 5 to 8 km/s. The precise speed varies according to the region of the Earth’s interior, from less than 6 km/s in the Earth’s crust to 13.5 km/s in the lower mantle, and 11 km/s through the inner core.
What is the interval between the P wave and S wave?
S waves are indicated by an abrupt change in wave amplitude. In the seismogram below, we see that the S wave arrived at about 34 sec after the P wave arrived. This time difference is called the S-P interval and is the lag time between the P and S wave.
How do you read a SP interval?
Measuring the S-P interval You have to measure the interval to the closest second and then use a graph to convert the S-P interval to the epicentral distance. On the sample seismogram at the right the vertical lines are spaced at 2 second intervals and the S-P time interval is about 36 seconds.
Why didn’t the P waves arrive in each city at the same time?
Answer Expert Verified P-waves of primary waves originate from the epicenter. Since each city has a different distance from the epicenter, the p-waves will arrive at different times.
Which point is closest to the epicenter?
The point within the earth where the actual movement takes place is called the focus. As shown in Figure 1, the point on the surface directly above the focus is called the epicenter….
|P-wave arrival time||12:08-45 MST|
|S-wave arrival time||12:10-15 MST|
What happens to the time difference between primary and secondary waves as the distance traveled gets longer?
What happens to the times difference between primary and secondary waves as the distance traveled gets longer? The time differences become bigger. Suppose a primary and secondary wave both travel a distance of 4,000 km before they are picked up by a seismograph.
Why is three the minimum number of stations necessary to locate an epicenter?
The actual location of the earthquake’s epicenter will be on the perimeter of a circle drawn around the recording station. The radius of this circle is the epicentral distance. With two stations the epicenter could only be located as a point on a line. Three stations are needed in order to “triangulate” the location.
What is the minimum number of seismographs needed to locate an epicenter?
To find an earthquake epicenter you need at least three seismographs. Find the distance from each seismograph to the earthquake epicenter. The interception of the three circles is the epicenter.
What are the three different seismographs?
To overcome this problem, modern seismograph stations have three separate instruments to record horizontal waves – (1) one to record the north-south waves, (2) another to record east-west waves, and (3) a vertical one in which a weight resting on a spring tends to stand still and record vertical ground motions.
What are the steps to finding the epicenter of an earthquake?
Introduction: Steps to Locating the Epicenter of an Earthquake
- Measure the time that elapses between the arrival of the P (primary) wave and the arrival of the S (secondary) wave to the seismic stations.
- Using the S-P time, determine the epicentral distance of each station to the earthquake using a travel time curve.
Which types of earthquake waves will most probably be detected in zones A and B?
Which types of earthquake waves will most probably be detected in zones A and B? (1) zone A: P-waves, only; zone B: S-waves, only (3) zone A: S-waves, only; zone B: P-waves, only (2) zone A: P-waves, only; zone B: no P- or S-waves (4) zone A: S-waves, only; zone B: no P- or S-waves Page 3 5.
What is the approximate distance to the epicenter if the difference in the arrival times of the P wave and S wave is 5.5 min?
The S wave arrives 5.5 minutes after the P wave, so the epicenter is approximately_______ miles away.
What causes seismic waves to travel in curved paths?
The waves are refracted as they travel through the Earth due to a change in density of the medium. This causes the waves to travel in curved paths. When the waves cross the boundary between two different layers, there is a sudden change in direction due to refraction.
What happens when seismic waves travel deeper into crust?
Seismic stations located at increasing distances from the earthquake epicenter will record seismic waves that have traveled through increasing depths in the Earth. Molten areas within the Earth slow down P waves and stop S waves because their shearing motion cannot be transmitted through a liquid.
Why do you need to subtract the arrival times of the P and S waves?
The time between the arrival of the p-wave and s-wave becomes greater and greater as the distance from the epicenter increases because p-waves have a faster velocity than s-waves, meaning p-waves arrive at a station or location first, before s-waves, so as the distance from the epicenter increases, the distance that …
What is the approximate distance to the epicenter of the difference in the arrival times of the P wave and S wave is 5.5 min?
Which point in Figure 1 is the epicenter of the earthquake?
As shown in Figure 1, the point on the surface directly above the focus is called the epicenter. An earthquake epicenter can be located from records made of earthquake waves on devices called seismographs….
|Recording Station||Calculated Distance (miles)?|
|Salt Lake City:||miles|
What is the distance between the epicenter and the station for the earthquake recorded?
What happens to lag time the further you are from the epicenter?
Which of the statements best describes the relationship between lag time and distance from epicenter? The longer the lag time, the closer the distance. The shorter the lag time, the farther the distance. There is no relationship.