Hazards: Seismic Hazards (earthquakes) Flashcards
What are the primary hazards to earthquakes?
ground rupture and ground shaking
What are the secondary hazards of earthquakes?
Soil liquefaction, fires, building collapse, landslides/avalanches and tsunamis
What are the 5 forms of seismic hazards?
- earthquakes
- shockwaves
- tsunamis
- liquefaction
- landslides
What are earthquakes?
A sudden violent shaking of the ground, from the release of tension between plate margins
What are shockwaves?
Vibrations sent out by the focus of the earthquake (what we feel as the ‘earthquake’)
What are tsunamis?
Large waves caused by the displacement of large volumes of water
- can be triggered by underwater earthquakes and waves radiate out from the epicentre of the earthquake
What is liquefaction?
Soil is saturated with water, the vibrations of an earthquake can act like a liquid (makes the soil weak and deform)
What are landslides?
Shaking of the ground can dislodge rock, soil or snow causing landslides/avalanches that move downslope quickly
What is the spatial distribution of seismic hazards?
- most occur along plate boundaries (e.g. destructive or constructive)
- faults produce earthquakes at conservative plate boundaries (e.g. San Andreas Fault is a complex zone of fractures of crust)
- however they can occur away from plate boundaries, reactivation of old fault lines or human activity (fracking)
What is the magnitude and frequency of seismic hazards?
hundreds of low magnitude earthquakes happen globally everyday
earthquakes of high magnitude occur less often
What is randomness vs regularity of seismic hazards?
seismic hazards don’t seem to follow any clear pattern or trend, occurrence is largely random
What is the predictability of seismic hazards?
scientists can monitor the movement of tectonic plates to predict which areas are at risk
hard to tell when an earthquake will strike a particular place or the magnitude of it
What is the case study of an earthquake in a place of low HDI?
Haiti earthquake 2010
What are the characteristics of the hazard in Haiti?
- 7MMS
- destructive plate boundary
- focus was deep, 13km
What is the evidence of a disaster of Haiti earthquake?
- 160,000 deaths
- 188,000 buildings collapsed or destroyed
- $11.5billion in damages (120% of GDP)
What are the characteristics of the place/people in Haiti?
- unconsolidated geology and steep terrain
- corrupt government
- building codes not enforced
- dense, informal settlements
- poorest country in the western hemisphere
- high poverty (19% have access to sanitation)
- fatalistic attitudes
What is the case study of an earthquake in a place of high HDI?
South Napa Earthquake, California 2014
What are the characteristics of the South Napa earthquake?
- 6MMS
- conservative plate boundary
- shallow focus of 11km
What is the evidence of a disaster of South Napa earthquake?
- 1 death and 200 injured
- only older buildings suffered damage despite being retrofitted (4 destroyed)
- fires broke out
- $362 million in damages
What are the characteristics of the place/people in South Napa?
- stable government, building codes enforced including landuse planning
- well planned residential zones
- excellent emergency services
- adaptation perception
What 3 things affect the magnitude of an earthquake?
- margin type
- rate of movement of the plate (this is slightly unclear)
- depth of focus (deep focus, 300-700km, tend to have a higher magnitude however the waves have to travel further