Chapter 5

Question 1

Describe a megathrust fault.

Answer 1

The action of one block of a slope being thrust up and over another slope by the comprehensive stress of the system. This occurs on the whole boundary zone between a subducting and an overriding plate rather than a specific, easily defined plane.

Question 2

What are the 3 characteristics of a megathrust earthquake?

Answer 2

1.Occurs at an interplate zone where one plate subducts beneath another. 2.Occurs upon the release of a previously locked section. 3. has a magnitude greater than 7.0 and commonly in the range of 9.0

Question 3

What is the evidence of past megathrust earthquakes?

Answer 3

1. Tsunami evidence 2.Submerged coastlines (Downed trees and other vegetation in sediments) 3.Large underwater landslide debris

Question 4

When was there a megathrust earthquake just west of Vancouver Island? What size approximately?

Answer 4

January 26 1700, 9.0 magnitude

Question 5

Describe the tectonic plate position in North Western North America 80 MYA

Answer 5

Pacific plate to the west, Kula plate to the north, and Farallon Plate to the east

Question 6

Name the existing fragments of the unsubducted portions of the Farallon plate

Answer 6

The EXPLORER (to the north), THE JUAN DE FUCA (the largest), THE GORDA (on the southern tip, Cocos (west of mexico)

Question 7

What did the already subducted fragments of Farallon have an effect on?

Answer 7

These portions had an transforming motion effect of the North American Plate.

Question 8

What faults were created by the Farallon Plate subduction?

Answer 8

The Queen Charlotte Fault (in the north) and the San Andreas Fault to the south.

Question 9

What did Lewis and Clark encounter in Oregon that was indication of a Tsunami?

Answer 9

Strange stumps of large trees sticking up out of the salt rich mud of the columbia river flats near the pacific ocean, also many chaotically strewn boulders.

Question 10

After Japanese Scientists’ detective work when was the North American Tsunami determined to have happened?

Answer 10

Tuesday 26 January 1700

Question 11

How high was the 1700 tsunami in Washington State? In Japan?

Answer 11

10m Washington, 5m Japan

Question 12

Is there a pattern in megathrust earthquakes on the Pacific Coast?

Answer 12

No.

Question 13

What happens before and after the stress and release of stress in a megathrust earthquake?

Answer 13

Rocks in the vicinity of the thrust zone must be greatly deformed during the compresion. This process results in a progressive uplift of and bending of the front edge of the continental plate. Upon release the plate collapses downward, producing megathrust.

Question 14

What Seismic event was likely the largest in the last 100 years? When did it occur?

Answer 14

Chile, 1960

Question 15

Describe the Plates involved in the 2004 Tsunami.

Answer 15

Indo-Australian Plate (Comprised of the Burma and Sunda Subplates) and the Eurasian Plate

Question 16

What was the Microplate produced in the Indo-Australian Plate 40-50 MYA called?

Answer 16

The Andaman Microplate

Question 17

What was the length of the ruptured plate that caused the 2004 tsunami?

Answer 17

1300km

Question 18

What is the Japanese meaning of the word Tsunami?

Answer 18

Tsu = harbour, nami = wave

Question 19

Why is seismic sea wave or tidal wave the wrong word to describe a tsunami?

Answer 19

This is because tsunamis can be caused by earthquakes, landslides, violent volcanic eruptions or meteoroid/asteroid impacts.

Question 20

What is the speed of a tsunami related to?

Answer 20

Water Depth

Question 21

Describe the Imamura-Iida scale of Tsunamis and their frequency in the Pacific Ocean.

Answer 21

4 = partial or complete destruction of manmade structures, flood deep inland (1 in 10 years). 3 = Heavy structures near the sea damaged, some flooding inland,ships carried inland or out to sea (1 in 3 years). 2=Large, flooding of the shore to some depth, some damage to solid structures (1 per year). 1 = Generally noticed, light sailing vessels carried out to shore,reversal of river flow in estuaries (1 per 8 months). 0 = slight, waves noticed (1 per 4 months) -1 = Only noticed on gauge records

Question 22

How is tsunami generated?

Answer 22

A tsunami is generated by any disturbance that displaces a large water mass from its equillibrium position (i.e. not just megathrusts)

Question 23

How can a Tsunami be generated from an underground occurance other than a sudden shift in the height of the seafloor?

Answer 23

Submarine Landslides (DUH)

Question 24

What happens in terms of energy distribution as the tsunami approaches the shallow waters?

Answer 24

The tsunami approaches land and the depth becomes shallower and shallower. However the energy of the tsunami must be mantained (due to equillibrium distribution of energy and momenta). There is very little friction and thus the speed of the wave reduced via shallow waters transfers it’s joules into wave height. CALLED THE SHOALING EFFECT.

Question 25

What happens at the shoreline as the Tsunami approaches?

Answer 25

The DRAW-DOWN EFFECT occurs where the water will recede rapidly into the ENCROACHING WAVE.

Question 26

What was the time between the 1st and 2nd waves during the Krakatau volcanic eruption?

Answer 26

2 hours

Question 27

What was the highest wave ever experienced, what was it’s speed and where did it occur?

Answer 27

524 meters, between 150 and 210 km/hour and in Lituya Bay, Alaska

Question 28

What is the warning center for tsunamis in the pacific called?

Answer 28

Pacific Tsunami Warning center (PTWC)

Question 29

What organization administers the warning center for tsunamis in the pacific?

Answer 29

The USA’s National Oceanic and Atmospheric Administration (NOAA)

Question 30

What are the 3 objectives of the PTWC?

Answer 30

to detect earthquakes in the region, see if a tsunami was generated, and to provide warning to at risk populations if one was

Question 31

How many countries are participating in the PTWC?

Answer 31

26

Question 32

Describe the event that catalyzed the beginning of the PTWC.

Answer 32

April 1, 1946, two large subduction ruptures occurred in the aleutian trench, 8.1 earthquake. A 30.5 m high wave wiped out a coast guard lighthouse killing the 5 inhabitants, hit Hawaii and wiped out the city of Hilo, 159 killed