# Describe the relationship between time lag and distance from epicenter

### Calculating the Epicenter of Earthquakes - Maple Programming Help

Calculating the Epicenter of Earthquakes Main Concept Seismology is the study of earthquakes, their To determine the distance of an earthquake epicenter: 2. Calculate the difference between the arrival time of the P-wave and the S-wave . E-mail Address (Optional). What is? This question helps us to combat spam. A. Determining Time Lag: A seismograph records earthquake activity by plotting Please describe the relationship between distance from the epicenter and P. Figure 1 - Our typical seismogram from before, this time marked for this exercise ( from Finding the Distance to the Epicenter and the Earthquake's Magnitude.

One type of seismograph is a visible recording machine, shown in Figure 2. A pen draws a pattern of the waves on paper that is attached to a revolving drum.

The wave record from a seismograph is known as a seismogram - see Figure 3. A typical seismogram of an earthquake has three prominent wave patterns.

### How Do I Locate That Earthquake's Epicenter?

The first waves to arrive are the P-waves also called "primary" or "push-pull". They are followed by the S-waves also called "secondary," "shear," or "shake".

Finally, the L-waves "long" or "Love" arrive. This investigation contains the seismograms from three different stations for an earthquake. See how accurately you can locate the epicenter of this quake.

Earthquake epicenter and focus Figure 2: As the P and S waves travel out from an earthquake the P waves get progressively farther ahead of the S waves. 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. The distance of a seismic station from an earthquake is easily determined from the S-P interval, the time difference between the time of arrival of the first P wave and the first S wave.

To determine the location of an earthquake the distance of the earthquake must be determined from at least three seismic recording stations.

Circles with the appropriate radius are then drawn around each station.

- Epicenter Triangulation HomePacket

The intersection of three circles uniquely identifies the earthquake epicenter. Earthquake Magnitudes Richter magnitude: The Richter magnitude is a measure of the amplitude of ground movement.

Because the amplitude recorded on seismograms will decrease with increasing distance from the earthquake the distance must first be determined so that it can be corrected for.

### What is the relationship between lag time and distance from an earthquake's epicenter

The Richter magnitude of an earthquake can be easily determined from the S-P interval combined with the maximum motion recorded on the seismogram. The Richter magnitude is recorded on a logarithmic scale on which an increase of one represents a ten times increase in amplitude. For example, a magnitude 5 earthquake produces ten times greater ground motion than a magnitude 4 earthquake. Moment magnitudes measure the amount of stress energy released in an earthquake.

They are calculated after determining the fault throw distance the fault movedthe area broken on the fault depth and lengthand the rigidity of the fault rocks the springiness of the rocks. Moment magnitude is also recorded on a logarithmic scale on which an increase of one represents a 32 times increase in the stress energy released.

In order to better understand the long term behavior of a given fault it is necessary to go back to written records of earthquakes that occurred before seismic recording began. An intensity of I not felt to XII total damage is designated according to the amount of damage cited in historic records. Complicating factors include differences in building design weaker vs. To determine the Richter magnitude of an earthquake, seismologists need to know the distance to the earthquake and the amplitude of the surface wave at the recording site.

The distance of the seismic recording station from the earthquake epicenter is determined from the time difference between the first arrival of the P-wave and the S-wave.

This is known as the S-P interval. The recorded surface wave amplitude, measuring how many millimeters the ground moves at the seismic station, will depend on the distance from the earthquake epicenter and the magnitude of the Earthquake.

Since each block is worth 10 seconds on the first graph, we must find the one vertical line that lies between the P and S curves that is exactly 9 blocks long.

That one vertical line indicates that the Lower Station is about km from the epicenter. The second graph is included for times shorter than 60 seconds.

As these waves travel through the Earth, they will change speed according to the type of rock that they are travelling through. For very short time lags, under 60 secondsthe following formula can be used to calculate the distance to the epicenter.

## Online Help

Using the formula, see if you can determine the distance of the two seismograph stations from the earthquake epicenter. Please describe the relationship between time lag and distance from the epicenter.

Use data from this sheet to substantiate your answer. Please describe the relationship between distance from the epicenter and P wave arrival time. Using the math formula above, we can easily determine that this seismograph station is a distance of km from the epicenter. Does this tell us exactly where the earthquake epicenter was located?

## What is the relationship between time lag and distance from the epicenter?

All we know at this point is that the epicenter is located somewhere along a circle of points exactly km from the single seismograph station. To accurately pinpoint the location of an earthquake epicenter, we need seismograph data from a minimum of three locations. Using data from three seismograph stations to locate an earthquake epicenter is a process known as triangulation. The following exercise will give you an opportunity to practice the process of triangulation to locate some earthquake epicenters.

Below are seismograph readings for two separate earthquakes. For each seismograph reading, determine the time lag. Using the process of triangulation, follow the instructions on the following page and use the map to locate the epicenters of five earthquakes.