Earthquakes What if you knew the epicenter was 572 km from Vancouver Earthquakes What if you ALSO know that it is 884 km from Prince Rupert Earthquakes Finally you also know that the epicenter is ID: 628459
Download Presentation The PPT/PDF document "Interior Processes Locating earthquakes" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Interior Processes
Locating earthquakes
EarthquakesSlide2
What if you knew the epicenter was
572
km from Vancouver?
EarthquakesSlide3
What if you ALSO know that it is
884
km from Prince Rupert?
EarthquakesSlide4
Finally, you also know that the epicenter is
637
km from Victoria.
Where is the exact location of the epicenter?
EarthquakesSlide5
Locating the epicentre
Information from
3 different
seismograph stations is needed to locate an epicentre.
This is
triangulation: 3 circles are drawn on a map and where the 3 circles intersect is where the earthquake epicentre is located.
Rocks & MineralsSlide6
EarthquakesSlide7
Locating the epicenter
In order to find the distance between any seismograph station and the epicenter, we make use of the
difference in arrival times
between the P and S waves.Slide8
What do you notice about this seismogram?
Since P waves travel
faster
than S waves, the first zigzags on the seismogram represents
the
arrival of P waves
The S waves arrive
second
and then surface waves arrive
last
EarthquakesSlide9
We can make use of this time lag to determine how
far
the seismograph station is from the epicenter.Slide10
Analogy
EarthquakesSlide11
Determining the
distance to an epicentre:
Earthquakes
The
further
away a detecting station is from the earthquake’s
epicenter,
the
larger
the gap between P and S waves arrival
times.
The
relationship between
P and
S waves travel
times and
epicentre is
shown on a
Travel-Time Graph
(p. 275)
.
If
the
difference in arrival
times is known, the distance to the epicentre can be
found.Slide12
Here’s a sample problem
:
P waves arrive at a seismic station
4
:30 (
4
minutes
30 seconds
)
before the S
waves from the
same earthquake
.
How
far from the
epicenter is
the seismic station?Slide13
Here’s what you know:
P
& S
waves arrive
at a seismic station 4 minutes
and 30
seconds (4:30)
apart.
Here’s
what you need to do to find the distance to the epicenter:
Take
a sheet of paper and line
up the
left edge with the vertical
axis (
time). Be sure that most of the
paper is
hanging down below the graph.
This is
important.
2) Make a small, thin, and
accurate
mark
on the paper at 0 time. Make another
small, thin, and
accurate
, mark at 4:30
(4 minutes, 30 seconds).
Your 2 marks are now 4:30 apart!Slide14
3) Now
slide your paper to the right
until one of your marks is
exactly
on the S wave line and the other
is
exactly
on the P wave line. It is
very important to be sure your
paper is straight (vertical).
4) Now
look to see where
the bottom of
your paper crosses the
lower (
epicenter distance) axis. In
this case,
it crosses at
exactly 3000 km.
When
P & S waves arrive 4
minutes and
30 seconds apart it means
that the
seismic station is exactly
3000 km
from the epicenter of the quake
.Slide15
Practice:
This is a seismogram from a seismograph located in Vancouver. How far away is the earthquake epicenter?
Earthquakes