L4-6 earthquakes

Question 1

The New Zealand plate boundary

Answer 1

Australian plate to the west
Pacific plate to the east

Puysegur subduction zone: australian plate subducts underneath pacific plate

Alpine/marlborough fault system: continental-continental strike slip and reverse fault (oblique)
25 mm/yr dextral strike slip and 10mm/yr dip-slip

Hikurangi subduction zone: pacific plate subducts underneath australian plate
20-40 mm/yr slip rates

Taupō volcanic zone: back-arc extension on the australian plate north island dextral belt (fault type)
10 mm/yr slip rates

Question 2

Earthquake

Answer 2

Incremental slip on a fault in response to moving tectonic plates
Releases of energy some of which is converted to seismic waves

Question 3

Relationship between earthquake cycle, fault slip rates, and fault recurrence intervals

Answer 3

Fault recurrence intervals: the period of time between earthquakes

Fault slip rates: combine recurrence interval with amount of displacement and you get slip rate

Earthquake cycle: earthquake cycle is the elastic rebound combined with slip rates (idk i think its just bigger picture slip rate)

Question 4

Geologic and geodetic methods to obtain fault slip rates

Answer 4

Look at evidence for markers of displacement and date these areas

Excavate a trench. earthquake ages constrained from offset sediments

Two GPS stations can be used to look at elastic rebound. coseismic and interseismic

Question 5

Seismology and measuring earthquake locations and magnitudes

Answer 5

Location: difference in velocity between P and S waves. arrival times used to estimate distance to the earthquake hypocentre. as long as more then one seismometer picks it up they can compare the difference and use it to locate hypocentre

magnitudes: related to logarithm of the amplitude of a seismogram, corrected for distance and instrument response

Question 6

Gutenberg-Richter and Omori Laws

Answer 6

Gutenberg-Richter: describes earthquake magnitude frequency relationship. often the larger the earthquakes the further between them. inaccurate for small earthquakes because seismometers do not detect them and large earthquakes because we don’t have the timescale they occur on

Omori law: rate of aftershocks decreases predictably as a function over time. not linear or constant

Question 7

Hazards vs Risk

Answer 7

Hazard: a phenomena with the potential to cause harm

Risk: hazard + exposure. people need to be there

Question 8

Earthquake hazards

Answer 8

Ground motion
Landslides
Liquefaction and lateral spreading (fluid pressure increases so it can push grains apart to move from high to low pressure)
Tsunami
Surface rupture (damage to buildings due to surface deformation)

Question 9

Probabilistic seismic hazard analysis

Answer 9

1. defining sources
2. magnitude frequency distribution for sources
3. ground motion models (how particular areas move/spread)
4. hazard curves