1. LOCATING AN EPICENTER X

2. Earthquakes occur in many distance places, and many of them occur under oceans. However, a seismologist with suitable equipment does not have to be near one to determine its location, depth, and magnitude. The violent movement within the earth that we call earthquakes dissipate some of their energy in the form of waves (called seismic waves) radiated in every direction form the points within the earth where the rock material has actually moved. Such a point of movement is called the focus of an earthquake. Sensitive instruments called seismometer detect these waves, and other instruments, called seismographs, record the time of arrival and the intensity of these wave patterns. With three such records (called seismograms), a seismologist can rather easily locate the epicenter, the point on the earth's surface directly above the focus of the earthquake, and determine the magnitude of the earthquake.

3. seismic waves
the energy waves given off by an earthquake.

4. focus
the place where an earthquake originates.

5. seismometer
instrument that detect seismic waves.

6. seismograph
an instrument used to detect and record seismic waves.

7. epicenter
the point on the earth's surface directly above the focus of the earthquake.

8. How many seismograms are needed to determine the epicenter of an earthquake?3

9. How to read the ESRT

10. Travel Time

11. 4 minutes 7 minutes 20 seconds p-wave p-wave
How long does it take a P wave to travel 2000 km?
2) How long does it take a S-wave to travel 2000 km?
3) Which wave is faster?
4) Which wave will reach a seismic station first?
4 minutes
7 minutes 20 seconds
p-wave
p-wave 11

12. 11 minutes 20 seconds 20 minutes 40 seconds
5) How long does it take a P-wave to travel 8000 km?
6) How long does it take a S-wave to travel 8000 km?
11 minutes 20 seconds
20 minutes 40 seconds 12

13. Difference in Travel Time

14. 7) For an earthquake that is 2000 km away, calculate the difference in travel time between the P-wave and S-wave. Show your work.
7 min 20 sec
- 4 min 00 sec
3 min 20 sec

15. 8) For an earthquake that is 8000 km away, calculate the difference in travel time between the P-wave and S-wave. Show your work.
20 min 40 sec
- 11 min 20 sec
9 min 20 sec

16. 9) As the distance between the earthquake epicenter and the seismic station increases, what happens to the time difference between the arrival of the P-wave and S-wave?
As the distance increases, the time difference increases.

17. difference increases
as distance increases..

18. Time Math (A) 1. 10:09:50 - 10:08:25 2. 09:45:10 - 09:25:10 3.
- 10:08:25 2.
09:45:10
- 09:25:10 3.
03:15:33
- 03:14:43 4.
07:22:55
- 07:21:55 5.
04:15:57
- 04:14:30 6.
01:24:43
- 01:22:05 7.
02:05:17
- 01:55:34 8.
08:17:05
- 07:30:05 9.
06:57:32
- 05:58:33
10.
8:17:28
- 7:45:36
11.
12:59:59
- 11:04:21
12.
05:02:03
- 04:59:59
13.
04:28:53
- 03:52:41
14.
07:49:36
- 04:03:51
15.
09:15:24
- 02:16:25
16.
11:25:14
- 01:02:19
20:00
:50
01:25
1:00
2:38
9:43
1:27
47:00
58:59
31:52
1:55:38
2:04
3:45:45
36:12
6:58:59
10:22:55

19. Time Math (B) ****** TO BE GRADED ******1.
02:50:45
- 02:50:31 2.
04:21:22
- 04:18:22 3.
08:28:37
- 08:22:53 4.
10:58:21
- 10:29:21 5.
07:41:31
- 07:32:48 6.
01:54:23
- 01:42:25 7.
11:09:21
- 10:42:52 8.
09:04:28
- 08:12:28 9.
02:49:24
- 01:50:25
10.
04:12:11
- 03:55:30
11.
08:55:58
- 06:09:19
12.
08:02:03
- 07:59:59
13.
04:26:50
- 03:53:44
14.
08:55:49
- 01:27:50
15.
10:15:33
- 03:16:21
16.
12:34:42
- 02:07:30
3:00
:14
5:44
29:00
11:58
26:29
8:43
52:00
58:59
16:41
2:46:39
2:04
7:27:59
33:06
6:59:12
10:27:12

20. If you know the difference between the arrival time of the p-wave and the arrival time of the s-wave, you can use the graph to determine the distance to the epicenter.

21. difference increases as distance increases..21

22. Distance to the Epicenter
5 STEPS
#1) Calculate the difference between the arrival time of the p-wave and the arrival time of the s-wave.

23. 1 – Complete ‘S – P column’.
2 – Check your answers.
STATION
P ARRIVAL TIME
S ARRIVAL TIME
S-P
DISTANCE A
14:05:25
14:08:00 B
14:13:15
14:22:20 C
14:08:15
14:13:05

24. A 07 60 X X
14:08:00 -
14:05:25
00:02:35 B
14:22:20 -
14:13:15
00:09:05 12 65 C X X
14:13:05 -
14:08:15
00:04:50

25. STATION P ARRIVAL TIME S ARRIVAL TIME S-P DISTANCE A 14:05:25 14:08:00B
14:13:15
14:22:20 C
14:08:15
14:13:05
00:02:35
00:09:05
00:04:50 25

26. 2) Take a piece of paper and place the edge next to the travel-time scale on the graph.
(ESRT p.11;
P-wave, S-wave chart).

27. 3) Mark off a distance on the edge of the paper that represents the difference in travel time between the p-wave and s-wave.
Example;
time difference
of 2 minutes.

28. 4) Move the edge of the paper with the time marks on it across the graph until the upper mark is on the S-wave curve, and the lower mark is on the P-wave curve.
(Be certain to keep the paper's edge parallel to the vertical distance lines.)
Example;
time difference
of 2 minutes.

29. 5) When you have found where the time marks on the paper are exactly on the P and S wave curves, read the distance scale that corresponds to this difference in arrival time.
Example;
time difference
of 2 minutes.
1100 km

30. Determine the distance to the epicenter
STATION
P ARRIVAL TIME
S ARRIVAL TIME
S-P
DISTANCE A
14:05:25
14:08:00 B
14:13:15
14:22:20 C
14:08:15
14:13:05
00:02:35
00:09:05
00:04:50 30

32. STATION P ARRIVAL TIME S ARRIVAL TIME S-P DISTANCE A 14:05:25 14:08:00B
14:13:15
14:22:20 C
14:08:15
14:13:05
00:02:35
1500 km
00:09:05
7700 km
00:04:50
3300 km 32

33. To Determine arrival time
00:20:50
00:29:50

34. A
00:20:50
00:29:50
9:00
7800
11:10
00:09:40
00:18:35
00:25:45
7:10
5500
8:50
00:09:45
00:16:05
00:20:50
4:45
3200
5:55
00:10:10

35. A)
San Jose (7800 km)
1 cm X =
500 km
7800 km
New York (5500 km)
1 cm X =
500 km
5500 km
San Francisco (3200 km)
1 cm X =
500 km
3200 km

36. B
00:19:20
00:22:40
3:20
2050
4:00
00:15:20
00:21:33
00:25:45
4:15
2750
5:10
00:16:20
00:20:20
00:24:50
4:30
3000
5:35
00:14:45 36

37. 37

38. #
P-wave
Arrival time
S-wave
Difference in
Distance to Epicenter
P-wave Travel Time
Travel time
Origin Time 1
6:45 pm
6:48 pm 2
3:06:20
3:10:20 3
17:11:00
17:16:40 4
10:38:40
10:45:40 5
21:21:20
21:29:00 6
2000 km
06:00:00 7
11:00
05:37:24 8
07:00
12:36:46 9
11:24:23
15:20

40. #
P-wave
Arrival time
S-wave
Difference in
Distance to Epicenter
P-wave Travel Time
Travel time
Origin Time 1
6:45 pm
6:48 pm 2
3:06:20
3:10:20 3
17:11:00
17:16:40 4
10:38:40
10:45:40 5
21:21:20
21:29:00 6
2000 km
06:00:00 7
11:00
05:37:24 8
07:00
12:36:46 9
11:24:23
15:20
03:00
1800 km
03:40
06:40
6:41:20pm
04:00
2600 km
05:00
09:00
03:01:20
05:40
4000 km
07:00
12:40
17:04:00
07:00
5400 km
08:40
15:40
10:30:00
07:40
6200 km
09:40
17:20
21:11:40
06:04:00
06:07:20
03:20
04:00
07:20
05:48:24
05:57:24
09:00
7600 km
20:00
12:45:26
12:52:26
5400 km
08:40
15:40
11:17:33
06:50
5200 km
08:30
11:09:03

41. Earthquakes and Igneous Activity, Including Volcanoes.

42. Earthquake -
The shaking of Earth’s crust caused by a release of energy.
the energy is given off as seismic waves (or earthquake waves).

43. Four causes for Earthquakes;
1) Volcanic Eruption.
2) Collapse of a cavern.
3) Impact of a Meteor.
4) *** Movement along faults.

44. The cause for most of the major earthquakes is….
The strain that builds up along plate boundaries.

45. Epicenter vs. Focus of an earthquake.
the point at which the first movement occurs during an earthquake.
Epicenter -
the point on Earth’s surface directly above the focus.

46. epicenter
focus

48. Measuring seismic (earthquake) waves.
A seismograph is the instrument that measures seismic waves.

49. A seismogram is the recording (wiggles) of the seismic waves.49

50. 1) P-wave - also known as…..
We will examine two types of seismic waves.
1) P-wave - also known as…..
primary waves or
compressional waves.

51. Characteristics of p-waves;
Movement;
compress and release rock.
Types of Materials;
travel through solids, liquids, and air.
Velocity;
travel at the greatest velocity (the fastest moving waves).

52. 2) S-wave - also known as...
Secondary waves or
shear waves.

53. Characteristics of s-waves;
Movement;
move at right angles to the direction in which the wave is moving (side to side).
Types of Materials;
only travels through solids.
Velocity;
travels at about 1/2 the speed of p-waves (moves slower)

56. Velocity of seismic waves
velocity depends on the properties of the material that the wave passes through.
the greater the density of the material, the faster the waves move.
the greater the pressure, the faster the waves move.
waves will be bent when they pass from one type of material, to another.

57. P-wave paths through Earth

58. S-wave paths through Earth.

60. Location of an Epicenter
use the difference in time between the arrival of the p-wave, and the arrival of the s-wave.
the greater the difference between the arrival times, the further away the earthquake is.

62. at least three seismograph stations must be used.
each station produces one circle.
the epicenter is where the three circles meet.

64. Earthquake Review Epicenter vs. Focus
The point inside the earth where the first movement occurs is the …
focus
The location on the Earth's surface is the ……..
epicenter

65. P & S Waves Also known as… Group these words together according to the wave type.
Compressional
S-Wave
Primary
Secondary
P-Wave
shear

66. P-Wave
primary
compressional
S-Wave
secondary
shear

67. P-wave or S-wave. Compresses rock Slower moving wave
Only travels through solids
Travels at a greater velocity
Displacement is at right angles to the movement of the wave
Travels through solids, liquids, and gases P S S P S P

68. Origin Time of Earthquakes
When did the earthquake occur?
arrival time – travel time = origin time
arrival time
origin time
travel
time

69. Example
If the s-wave first arrived at a station at 10 hr:12 min: 30 sec and the seismograph is 5500 kilometers away, when did the earthquake occur?
s-wave
arrival time 10 hr: 12 min: 30 sec
distance 5500 km

71. s-wave travels 5500 km in…..
16 minutes.
10 hr: 12 min: 30 sec
- 16 min
9 hr: 56 min 30 sec = origin time

72. Magnitude of Earthquakes
the closer to the epicenter, the greater the damage.
magnitude scale –
uses the height of the wiggles on the seismograms to infer the amount of energy releases by an earthquake.
lowest value is less than 1.
highest value ~ 9.5 (rocks break above this number)

73. Earthquake Hazard
most injuries are caused by parts of falling buildings.
we can not predict earthquakes.

74. Emergency Planning “Drop, Cover, and Hold. drop under a strong object.
turn away from windows and cover your eyes.
hold onto the object you are under.
Do not run out of the building…
most earthquakes only last seconds.
Planning…. building codes / techniques.

75. Tsunami Japanese – “a harbor wave”
it is a large wavelength ocean wave produced by disruption of the ocean floor.
caused by an earthquake, volcanic eruption, or landslide.

76. MODEL OF EARTH’S INTERIOR

77. Seismic waves give us information about the interior of the earth.
layers, composition, density, etc.
see Earth Science Reference Tables, page 10.
complete practice questions.

78. ESRT p.10

79. List the layers of the Earth, from the surface down through the interior.
crust 1) 2) 3) 4) 5) 6)
lithosphere
rigid mantle
asthenosphere
mantle
stiffer mantle
outer core
inner core

80. 2) Name the two types of crustal material.
1 - continental
2 - oceanic

81. 3) How do the two types of crustal material compare in density and composition [and thickness]?
1 – continental density 2.7 (low) granitic comp [thick]
2 – oceanic density 3.0 (high) basaltic comp [thin]

82. 4) Which layer of the Earth’s interior has the greatest density?
inner core
5) Which layer of the Earth’s interior has the lowest density?
continental crust

83. 6) What is the pressure at 2200 km depth?
1 million atmospheres

84. 7) Which layer of the Earth’s interior has the greatest pressure?
inner core

85. 8) What is the temperature at a depth of 3000 km?
5000 OC

86. 9) Which layer of the Earth’s interior has the greatest temperature?
inner core

87. Zones of Earth

88. lithosphere
is composed of the crust and the upper portion of the mantle (“rigid mantle) 88

89. crust the outer most part of the earth. there are two types of crust;
continental crust
oceanic crust

90. continental crust makes up the continents.
it is thicker (thickest in mountain ranges).
granitic composition
(like granite).
lower density.

91. oceanic crust makes up the crust beneath the oceans. it is thinner.
basaltic composition (like basalt).
higher density.

92. Moho (Mohorovičić discontinuity) (MOE-HOE-ROE-vee-cheech)
(discovered in 1909 by Andrija Mohorovicic , a Croatian seismologist.)
the boundary between the crust and the mantle.
red line

93. Mantle located below the crust. contains 80% of Earth’s volume.
it is divided into three parts
upper rigid mantle
asthenosphere
lower stiffer mantle

94. asthenosphere partly molten plastic-like
allows plates of the lithosphere to move around Earths surface.
magma and lava originate here.

95. Core located below the mantle. composed of iron and nickel.
(evidence; meteorite composition, seismic waves)
divided into two parts
outer core – a liquid.
inner core - a solid.

96. Shadow Zone
location on the earth’s surface that will not receive seismic waves from an earthquake.
~ 100 to 143 degrees away from the epicenter.

99. Shadow Zone no waves Shadow Zone no waves
Simplified ‘Shadow Zone” diagram
Shadow
Zone
no waves
receive both
p-waves &
s-waves
receive
only
p-waves
core
epicenter
Shadow
Zone
no waves