###### Asked in Earthquakes

Earthquakes

# What two seismic wave types are used to determine the distance of the seismic station from an earthquake?

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## Related Questions

###### Asked in Earthquakes

### How do you know where the epicenter of the earthquake is?

Where the most Movement is in the Earthquake.
Seismic arrays are sensitive enough that even at great distance
seismic waves are picked up; using these large arrays of station
recordings and associated distance algorithms a precise location of
the shock can be deduced. the more concentrated the array around
the immediate quake location and the magnitude of the earthquake
improve accuracy of event locations.
Additional Information:
You would use a seismograph to determine the magnitude of an
earthquake and the distance to the earthquake. You can then use
three seismographs that measured the same earthquake to triangulate
determine the epicenter.

###### Asked in Earthquakes, Plate Tectonics

### How do you figure out the distance of an epicenter?

The distance of an epicenter from a seismograph station can
determined by the time it takes for the seismic waves to reach each
station. You need at least 3 seismic stations to record the event
to determine this. The time taken for each seismic station to
resisted the event will be different as they are different
distances from the epicenter. The distance to the epicenter can
then be calculated for each station and a epicenter can be
determined by a triangulation from all stations that have
registered the event.

###### Asked in Algebra, Geometry, Earthquakes

### How do you use circles to find the epicenter of an earthquake?

Scientists can calculate the distance that an earthquake occurs
from a seismometer station by looking at the record of the seismic
waves and measuring the difference in time between the arrival of P
and S-waves.
This gives them a distance but not a direction. So they plot
this distance on a map by drawing a circle round the seismometer
station. The radius of this circle is equal to the distance to the
epicentre.
If this is done for one other seismometer station that has
recorded the earthquake then the circles will intersect in two
places. If you add in a 3rd station and so a third circle they will
all intersect in one place - the epicentre of the earthquake.
In reality this process is automated by computer and lots of
readings from lots of stations are used.

###### Asked in Science, Earth Sciences, Earthquakes

### What is an epicentral distance?

"Epicenter" usually refers to a point on the Earth's surface
directly above the "focus" of an earthquake. When a quake occurs, a
seismic monitoring station can determine how far away it was from
the shock wave pattern -- that is called the "epicentral distance"
-- but not the exact direction. But with three or more monitoring
stations' epicentral distances, one can draw intersecting circles
to pinpoint the exact location.

###### Asked in Science, Internet, Physics, Waves Vibrations and Oscillations

### Why are longitudinal waves called primary waves?

Longitudinal waves that are produced by earthquake are called
primary waves because they are detected by seismometers before the
other types of seismic waves due to their higher velocity which
means they travel from the epicentre of an earthquake to the
seismic station more quickly than the other types of seismic
waves.

###### Asked in Earthquakes, Geology, Earth Sciences

### Which earthquake waves are the first to be recorded on a seismometer and are the fastest?

P-waves which are a compression or pressure wave are the fastest
seismic waves. As they are the fastest they will reach the seismic
station before any of the other seismic waves and be recorded
first.
Seismologists can use the difference between the arrival times
of different seismic waves to calculate the distance and ultimately
the location of the earthquakes epicentre.
For information on this, please see the related question.

###### Asked in Geophysics, Earthquakes

### What is the number of seismic stations need to find the epicenter of an earthquake?

Technically you just need one, but the more there are, the
easier it is to locate the epicenter of the earthquake.
The reason for this is that based on the timing of each of the
three seismic waves that reach the station, the station can
calculate a radius all around the station. So picture a circle with
what the radius is around the station, another station will do the
same thing, and there HAS TO BE an intersection of these circles
somewhere, so that narrows down the location of the epicenter.
Hope this makes sense.

###### Asked in Earthquakes

### Why is three the minimum number of stations necessary to locate an epicenter?

A single seismic station can tell you the distance to an
earthquakes epicentre but will give you no information on it's
location.
Seismic vibrations take time to travel to a seismic station and
when you have two seismic stations you can narrow down the location
of the earthquake's epicentre to two possible locations.
Add in a reading from a third station and you can nail down the
exact location because if you draw 3 circles one round each station
with the size of each circle proportional to the distance of the
station form the epicenter, they will intersect at one location on
the planet and that location is the epicenter.

###### Asked in Earthquakes

### How is the fact that P-waves travel faster that S-waves used to determine the distance of an earthquake epicenter from an seismograph station?

Using the difference in their arrival times and an estimate of
their velocity of propagation you can calculate the distance of the
earthquake epicentre from the seismometer recording station. If you
do this from three or more different seismometer stations you can
triangulate it's position.
For more information please see the related question.

###### Asked in Earthquakes

### How are the Richter scale and a seismograph used?

A seismograph (modern term seismometer) is an instrument that
measures the movement of the ground surface. During an earthquake,
seismic waves move or propagate away from the earthquakes epicentre
and cause the ground to move
A seismometer measures the acceleration at the grounds surface
as seismic waves pass by. They also record the frequency and
wavelength of the various waves along with their amplitude.
The Richter scale provides an estimate of the energy released by
an earthquake based on the amplitude of the seismic waves detected
at a seismometer station and a correction based on the distance of
the earthquakes epicentre from the station (as seismic waves lose
their energy as they propagate through the earth so if this
correction was not made, then different seismometer stations at
different distances would give differing Richter magnitudes for the
same earthquake).
The Richter scale itself is a logarithmic mathematical formula
which is calibrated so that a ten fold increase in amplitude
relates to a single hole number increase on the scale (e.g. an
earthquake with a Richter magnitude of 5 has seismic waves with a
maximum amplitude 10 times larger than those for a magnitude 4). It
has a number of practical limitations, in that it is poor at
recording earthquakes with magnitudes greater than 7 and at
distances greater than 650 km for a seismometer.
The equation for calculating the Richter magnitude (MR) is shown
below:
MR = (Log10A) - (Log10A0)
Where
A = maximum zero to peak amplitude of seismic wave (mm)
recorded.
A0 = Empirical function derived from the distance from
seismometer station to earthquake epicentre
Log10A0 From 0 to 200 km distance:
Log10A0 = 0.15 - 1.6 log(distance in km)
Between 200 and 600 km distance by:
Log10A0 = 3.38 - 3.0 log(distance in km)

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