lecture 16

Question 1

megathrust earthquake cycle

Answer 1

interseismic period: b/w earthquakes
- seafloor dragged downwards as plates r stuck and shortens as coastline bulges up
coseismic period: the earthquake
- fault slips, upper plate extends, seafloor uplifted, land subsides
after: tsunami waves spread out away from uplift which displaces and causes ocean-wide tsunami

Question 2

subduction zone

Answer 2

all oceans contain at least 1 subduction zone but pacific ocean contains the most
- most dangerous

Question 3

2004 indian ocean tsunami

Answer 3

boxy day - 9.2 megathrust in Sunda subduction zone

- third largest earthquake, fault length 1300km, 8 min rupture and slip 20m

Question 4

worst affected countries of 2004 indian ocean tsunami

Answer 4

1. indonisia: more than 2 hours after earthquake
2. sri lanka: earthquake not felt, peak arrived first
3. india ^
4. thailand: earthquake felt, preceded by drawback
5. myanmar
6. somalia
   total –> 228,000

Question 5

why was no alert issued 2004 indian ocean etsunami

Answer 5

didnt have ability to share information at the time and didnt have a warning system in place

Question 6

2011 tohoku tsunami

Answer 6

tectonic setting: westward subduction of pacific and phillippine sea oceanic plates beneat the japan arc on the continental eurasian plate

9. 0 tohoku earthquake ruptured megathrust fault
   - japan squeezed and elastic rebound

Question 7

cost of tohoku tsunami

Answer 7

1,5000 killed, mostly burning

economic: 360 bill USD

Question 8

run ups of tohoku

Answer 8

kuji: funnelled into bay, RU 13m
miyako: RU 39m
kesennuma: funnelled up river valley
sendai plain: RU 19m a distance of 8km
okuma: RU 15m, overtop 6m seawall and flood powerplant

Question 9

Japan GPS measurement

Answer 9

pioneered GPS measurements of sea floor motions

• ships use triangulation
• satellitles pinpoint precise locations
• GPS picks up signs of ground deformation

Question 10

why were the run ups larger than expected in tohoku tsunami

Answer 10

trench area was thought to be creeping and incapable of generating an earthquake, but slip was much larger than expected (mw 9.0) and ruptured up to trench, uplifting the sea-floor and creating large run up heights

Question 11

1700 CE orphan tsunami

Answer 11

ghosts forests in oregon washington discovered in 1980s trees were killed as they were lowered into salt water tidal zone by earthquake substidence

• radiocarbon dating and tree ring studies indicated forests were killed in 1700 CE
• records from Japan confirmed 2m high tsunami on january 21 1700

Question 12

average recurrence interval of orphan tsunami

Answer 12

similar events at 1310 CE, 810 CE, 400 CE, 170 BCE, 600BCE
average = 400-600 years
- suggested 15m run ups

Question 13

pacific tsunami warning center

Answer 13

set up in 1949, worlds first tsunami warning system
- uses seismogram data from around and assess:
- epicenter: did earthquake occur beneath sea
the depth: was it shallow enough to generate tsunami
magnitude: was it large enough to generate tsunami
if answers are yes then regional tsunami watch is issued and ugraded to tsunami warning if generated

Question 14

tsunami detection

Answer 14

deep ocean assesment and reporting of tsunami sensors added to pacific tsunami warning center in 200

• bottom pressure sensors
• communicate with floating buoy through accoustic telemetry, communicates with control centre thru satelites
• dart sensors

Question 15

WERA

Answer 15

wave radar run by ocean networks canada: shore based remote sensing system in tofino

• transmitting and receiving radar antennas that monitor opean current speed in real time
• can detectl arge waves up to 80km which can be 20min of warning

Question 16

tsunami evacuation

Answer 16

with knowledge of the shape of the coastline and the offshore bathmetry (seafloor topography) tsunami hazard maps can be used to predict wave heights at diff points along a
- raised earth parks can be built in cities where it is difficult to evacuate to high ground ex. padang

Question 17

tsunami mitigation

Answer 17

structural countermeasures include tsunami walls to block incoming waves, breakwaters and underwater berms to increase friction and dissipate wave energy and angled walls and ditches to steer waves away from vulnerable infrastructure

Question 18

1958 lituya bay tsunami

Answer 18

july 9, 7.8 earhtquake triggered huge rockfall
- giant slab of rock (30mill m) fell into the bay causing giant wave to run up hillside opposite, stripping trees of hillside

Question 19

nuuugaatsiaq tsunami

Answer 19

june 17 tsunami located on fjord in greenland
- 11 houses swept away and 4 killed
- triggered by landslide
landslide was so large it confounded in seismic signals making it seem like a mw 4 earthquake

Question 20

1929 grand banks tsunami

Answer 20

18 nov, Mw 7.2 earthquake occured in grand banks region, rich fishing grounds on eastern continental shelf
collapse of slope in huge submarine landslide
- deadliest earthquake in Canada 28 ppl

Question 21

how do we know about the 1929 grand banks landslide

Answer 21

formed turbidity current –> severed several trnsatlantic telgraph cables
around 100km ffrom epicenter an hour after and 700km away 13 hours

Question 22

cause of 1929 grand banks tsunami

Answer 22

abrupt increase in sea floor depth caused sea surface to warp downwards

1. r apid failure of shelf causes changes in sea floor
2. rapid response of sea level to changing depth generates tsunami
3. waves propagates outwards

Question 23

sieche

Answer 23

standing wave in enclosed or partially enclosed body of water, slosh back and forth
- can be set up by strong winds

Question 24

how to survive a tsunami

Answer 24

abandon belongings, dont stay to watch, get elevated as quickly as possible, dont return to the coastline