earthquakes and tsunamis

Question 1

what are the different environemnts which we can generate earthquakes?

Answer 1

number of different environments which can generate them. Seduction zones, continental rifts, and the end member of that rifting- the oceanic spreading ridge. Also volcanism and elsewhere can cause earthquakes.

Question 2

what is earthquakes distribution around the world?

Answer 2

Earthquake distribution: concentrated around the plate boundaries. Some random expectations. Mid ocean ridges cause earthquakes due to the processes geological: magmatism, volcanic activity, and got faults there, which can generate earthquakes.

Question 3

what is an earthquake?

Answer 3

• stress strain builds up over hundreds and thousands of years due to friction on a fault plane driven by motion between tectonic plates.

Question 4

how quickly do earthquakes release?

Answer 4

Releases in seconds or minutes, during an earthquake as one side of the fault moves past the other. Threshold point- moves and causes earthquake.

Question 5

what area of the earthquake determines its size/magnitude?

Answer 5

Size or magnitude: (seismic movement), depends on the area of the fault that moves, and the distance of movement along the fault plane.

Question 6

what is the Richter scale?

Answer 6

Earthquake magnitudes are logarithmic. Richter scale. Increase of 1 unit in magnitude corresponds to 10 x amplitude of seismic wave.

Question 7

what is the earthquake measured in?

Answer 7

Common scientific scale is moment magnitude Mw.

Question 8

what is a variet of fault slip behaviours?

Answer 8

Eg tsunami earthquakes involve slow rupture velocities and enhances tsunami amplitude relative to earthquake magnitude. This can be much more surprising tsunamis, as the earthquake was low.
Slow slip involves over weeks to months at a rate between plate boundaries displacement and earthquakes lip velocity. Slow, but building up massive movement.

Question 9

why study earthquakes and earthquake prone areas?

Answer 9

Cause loss of life and millions of pounds in damage every year.
Secondary effects, such as slope failure and tsunamis and liquefaction can cause significant damage.

Question 10

why do people try and understand past earthquake history?

Answer 10

Understanding the past earthquake history and current build up of stress and strain on an active fault allows us to determine areas at risk
Building codes can be set. local populations better mentally and physically prepared.
Not in a position to predict earthquakes on a useful human timescale. Due to the uncertainty of parameters involved

Question 11

what are secondary effects and related hazards of earthquakes? (6)

Answer 11

• Tsunamis
  
  • Slope failures (landslides, rockfalls, avalanches)
  • Liquefaction- shaken saturated sediment loses its strength and cannot maintain loads, behaves as a liquid. Bubbling up to the surface. Collapsed apartments in japan 1963 due to liquification.
  • Failure of coastal plains
  • Amplification of waves in sedimentary basins and soil related to bedrock. Eg, Mexico city.
  • 10% probability of being exceeded in 50 years. Typical one that’s used for GSHAP hazard map. PGA- peak ground acceleration. Earthquake in America which reversed the flow if the Mississippi river.

Question 12

what was important lesson about Haiti 2010 earthquake?

Answer 12

• Resilience and vulnerability for human consequences.

Question 13

what do earthquakes prone areas show?

Answer 13

Depends on the geography and geology. Depends at least as much on social and economic factors.

Question 14

what is vulnerability?

Answer 14

• Vulnerability is statistically greatest if you are poor, and if you live in a state with weak, corrupt or ineffective government.

Question 15

why should we improve the resilience of society?

Answer 15

• Improving the resilience of a society is expensive, and requires difficult political, economic, and social choices.

Question 16

what is a hazard?

Answer 16

Hazard is the source of potential damage. Risk is the probability of something or someone being damaged.

Question 17

what is a subduction zone?

Answer 17

X-section across accretionary margin. The pate boundary fault ruptures during a subduction zone plate boundary. They are the largest. This is because they are very long fault zones. They usually break in segments, a fraction of total fault length. Subduction zones fault areas are larger for same length due to the very LOW dip of fault plane. Near horizontal (greater area in brittle upper part of the crust/tectonic plate). Only areas which you can generate a magnitude of 9 or greater.

Question 18

why do subduction zones occur in submarine environments?

Answer 18

Because they occur in submarine environment, it doesn’t rupture the sea floor. Stress and strain builds up, deforming the sea floor. Stress on fault plane. This happens gradually over 100 of years. During the earthquake, the reverse of that movement occurs, and it slips. This what moves the water column and generates the tsunami. These travel fast in the deep ocean, but slow down when they reach the coast line. Submarine meteorite impact- rare and infrequent by catastrophic effects.

Question 19

what are the physics of earthquakes leading to tsunamis?

Answer 19

• Tsunami waves speed depends on water depth. Can be over 200 m per second in 5000 m of water
  
  • Speed is slower in shallow water
  • A wave propagating from deep to shallow water slows down. Water coming along behind tends to pile up, so the wave amplitude increases as it nears the coast line
  • Near shore variations cause changes in the form and height of the wave, and several individual waves typically arrive, spaced by many minutes or even hours.

Question 20

what is a POINT source?

Answer 20

• POINT source: eg, landslide, meteorite. Waves spread with distance and amplitude decreases.

Question 21

what is a LINE source?

Answer 21

• LINE source: waves don’t spread with distance and amplitude stays constant. Eg, faults are a line source. Subduction zone which has a length a few hundred metres long, holds a line source. These can be worse and more significant as it stays the same.

Question 22

what was 2004 Sumatran Margin, Indian ocean?

Answer 22

1600 km rupture. Convergence between the plates. Frequent place for earthquakes along the Burma plate. Uses coral ages to determine when earthquakes occurred. 9.2 earthquake. Average fault slip was 10 metres up to 30 to 40 metres. Fault rupture began at the hypocentre below the seafloor 30-40 km below the seafloor. Generated a tsunami with coastal waves up to 10 and 30 metres.

Question 23

What was 2004 Sumatran Margin impact on society?

Answer 23

This causes huge loss of life. Tsunami wave travelled fast in deep ocean. Locally the wave will arrive 25-30 minutes. 2 hours to travel to Sri Lanka. Limited time therefore warning systems need local organisation backed with education. This was the first earthquake of this magnitude since the development of modern geophysical techniques exploring the sea floe and sub-surface.

Question 24

what happened on 16th march, 2005?

Answer 24

another earthquake in the Sudan margin. Next segment south along the plate boundary posed serious hazard, due to the stress from the previous earthquake. 28th march: 8.6 Mw. Plate boundary ruptured, as warned, along a second major segment.

Question 25

what happened in 2009?

Answer 25

another, 7.6 Mw. Hypocentre 85km. BUT, the depth indicated this earthquake was not caused by the subduction pate, but the stress loading caused by the other earthquakes around seismic gap results in moment released here on a related fault. 1,000 fatalities. But the seismic gap on the plate boundary fault here still remains.

Question 26

what was the Japan Trench, 2011

9.0 Mw

Answer 26

Verified shallow slip to the trench, the edge of the subduction zone. Surprising- a lot of slip which occurred. 50-80metres slip in near-trench region, the LARGEST ever recorded fault slip. There were pressure gauges on the seafloor. Can record and quantify how much movement has been, therefore recorded the 80m slip.

Question 27

how was data already recorded from the Japan Trench?

Answer 27

• In the region of the greatest fault slip, bathymetric data has been collected prior to the earthquake. Data was recollected and the magnitude of vertical and horizontal motion determined by comparing the 2 datasets.

Question 28

how did they find information about Japan Trench in 2012?

Answer 28

• Unusual due to the methodologies never used before to quantify the slip.
  
  • They also dripped JFAST in 2012, drilling into the fault zone. Found the temperature increase related to some faults. Due to heat generated due to the faults. The signatures decrease as time goes on. Drilled 800 metres below the seafloor to reach the late boundary fault. The very large slip and slip to shallow depths is thought to be due to very weak clay layer that the fault forms within.