Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

EOS 170 > Lecture 7 - Earthquake Case Studies > Flashcards

Lecture 7 - Earthquake Case Studies Flashcards

1
Q

What types of earthquake are hosted by subduction zones and volcanic arcs?

A

Crustal earthquakes within the forearc
Megathrust events along the shallow plate interface
Outer rise normal faults from plate flexure
Intermediate depth (50– 300 km) intraslab events, often normal faulting
Deep earthquakes (300–700 km) within the subducting slab

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are some examples of intermediate depth earthquakes?

A

2001 Mw 6.8 Nisqually, Washington, USA
2017 Mw 7.1 Puebla, Mexico
2018 Mw 7.1 Anchorage, Alaska, USA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are some examples of fore-arc earthquakes?

A

2016 Mw 7.0 Kumamoto, Japan

1999 Mw 7.3 Chi-Chi, Taiwan

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the cycle of a megathrust earthquake?

A

The earthquake cycle on subduction zone megathrust faults involves vertical as well as horizontal motions.
During the interseismic period, the lower plate slowly subducts and the megathrust is locked. At the trench the upper plate is dragged downwards, but at the coast it contracts and bulges upwards.
During the coseismic phase, these motions are reversed. The mega- thrust slips, the upper plate rebounds westwards, the sea-floor at the trench is suddenly uplifted and the coastline subsides.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What type of earthquakes occur in continental plate boundary zones?

A

Usually upper crustal earthquakes only. The seismogenic zone is usually ~15 km thick.
Continental collision zones involve shallow earthquakes with a variety of mechanisms.
Continental shear-zones are characterized by shallow strike-slip faults.
Continental rifts involve shallow normal faulting earthquakes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is an example of a continental strike-slip boundary earthquake?

A

2019 Mw 7.1 Ridgecrest, California, USA earthquake

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is an example of a continental rift earthquake?

A

1959 Mw 7.3 Hebgen Lake, Montana, USA earthquake

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Why does the Alpine-Himalayan belt exist?

A

The Africa, Arabia and India continental plates are each moving northwards with respect to the Eurasia continental plate. This results in a broad zone of mountain building.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why do earthquakes occur along the edges of mountain ranges in Iran?

A

The mountains are being raised along thrust faults in response to the collision of the Arabian and Eurasian plates.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are some examples of Iranian earthquakes (Mw>6)?

A 
1978 Tabas (Mw 7.4) ~11,000 killed (~85% of population)
1981 Golbaf (Mw 6.6) ~1,400 – 3,000 killed
1981 Sirch (Mw 7.1) ~1,500 killed
1968 Dasht-e Bayaz (Mw 7.1) ~10,000 killed
1968 Ferdows (Mw 6.3) ~750 killed
1979 Ghaenat (Mw 7.1) A few hundred killed
1997 Zirkuh (Mw 7.2) ~1,500 killed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is InSAR and how can we use it to map earthquakes?

Which was one of the first earthquakes it was used on?

A

Large antenna simulated by combining multiple images along track (Synthetic Aperture Radar). Measure amplitude + phase of back-scattered energy.
The Bam earthquake was one of the first mapped using InSAR, a satellite radar technique.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How many people live in Tehran, Iran and why is this so concerning?

A

Around 14 million people.

Tehran was destroyed by earthquakes in 855, 958, 1177, and 1830 CE when it was only a small pit-stop on the Silk Route.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are intraplate earthquakes?

A

They are unusual, occurring far from plate boundaries. Plates are not perfectly rigid and can slowly deform internally. These earthquakes pose a significant hazard to central and eastern Canada.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What magnitude was the 2003 Bam, Iran earthquake?

A

Mw 6.6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Prior to the earthquake what was the desert city of Bam famous for?

A

The medieval citadel: the largest adobe (mud brick) building in the world and a UNESCO World Heritage site. It was destroyed in the earthquake along with much of the city.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What percentage of newer buildings in Bam were destroyed by the earthquake?

A

~60% of new buildings

17
Q

What percentage of old buildings in Bam were destroyed by the earthquake?

A

~90% of old buildings

18
Q

How many fatalities were there in the Bam earthquake?

A

26,000–40,000 fatalities (about half of Bam’s population).

19
Q

Where did the earthquake rupture the ground in the Bam earthquake?

A

The earthquake rupture runs along the foot of the Bam-Baravat Ridge.

20
Q

Why was the town of Bam so severely affected by the earthquake? (only Mw 6.6)

A

The ridge-bounding fault that ruptured in the earthquake is impermeable, so the water table dams against it. Tunnels called qanats tap into this water source. This forms the oasis that the city was built for.
Adobe brick buildings are very bad at withstanding earthquakes so almost all buildings in the city collapsed.

21
Q

Why are many Iranian towns and cities situated right next to active faults?

A

Many desert settlements in Iran owe their existence to active faults, which act as a water source in arid, tectonic landscapes.

22
Q

How are postglacial earthquakes triggered?

A

Postglacial rebound following melting of ice sheets causes crust to flex.
e.g. The Parvie fault scarp, Sweden, which formed in a single M ~8 earthquake ~10,000 years ago.

23
Q

What causes induced earthquakes?

A

Manmade stresses, especially associated with injection of fluids into the subsurface and changes in pore fluid pressure.

24
Q

Where are induced earthquakes known to occur?

A

Known occurrences of induced earthquakes include Oklahoma, Colorado, Texas, and NW Alberta/NE British Columbia.

25
Q

What is the “normal” frequency of Mw >3 events in

central US?

A

~25 per year

26
Q

What is the frequency of Mw >3 events in central US since 2009?

A

~330 per year

27
Q

What magnitude was the 2019 Mirpur, Pakistan earthquake?

A

Mw 5.6

28
Q

What depth was the Mirpur, Pakistan earthquake?

A

10 km

29
Q

How many people died as a result of the Mirpur, Pakistan earthquake?

A

30-40

30
Q

On what tectonic boundary does Mirpur, Pakistan sit on?

A

The continental collision zone between the Eurasian and Indian plate.

31
Q

Why was the Mirpur, Pakistan earthquake more deadly than it should have been?

A

Liquefaction along river
Basin amplification
Poor building standards
Lack of earthquake preparedness

32
Q

What did the 2011 Tohoku earthquake rupture?

A

The Japan Trench megathrust, where the Pacific plate subducts westwards beneath the Japan Arc.

33
Q

Why was the 2011 Tohoku earthquake significant?

A

The largest 20th C earthquakes (up to Mw 8.2) ruptured small mid-depth patches of the megathrust fault.
The shallowest megathrust was thought to be aseismic however it was actually ‘conditionally stable’ which allowed it to rupture all the way to the trench. This was previously thought to be impossible and Japan was unprepared for the strength of the earthquake and the tsunami that followed.

34
Q

How did the 2011 Tohoku earthquake effect assumptions about the Cascadia megathrust?

A

The assumptions about the strength of earthquakes on the Cascadia megathrust were drastically altered.

35
Q

What magnitude was the 2011 Tohoku earthquake?

A

Mw 9.0

36
Q

What happened to the east coast of Japan during the 2011 Tohoku earthquake? Were there any knock-on effects of this?

A

It moved eastwards and it lost height (moved downwards towards sea level). This movement of the coast into the sea displaced large amounts of water and caused a tsunami.

37
Q

What was the peak wave height of the tsunami caused by the 2011 Tohoku earthquake?

A

39 metres

38
Q

What is Paleoseismology?

A

The study of historic/prehistoric earthquakes using the sedimentary record.

39
Q

What did we learn about 2011 Tohoku tsunami due to paleoseismology?

A

There have been at least two previous tsunamis in that area of the same size as the 2011 one.

EOS 170 (22 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions