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T.1. Physical hazard profile the influence a hazardous impact (Spatial…
T.1. Physical hazard profile the influence a hazardous impact
Magnitude
Mercalli scale
observed effects to catagorise.
Hence and earthquake causing serious aftermath may score low on Richter scale but high on Mercalli scale
Haiti 2010 magnitude of 7 of Richter scale but XII on Mercalli scale. Killed 250,000 people
Scale I - XII
Richter scale
actual intensity of seismic waves.
Scale 1 - 10
Each increase in number increases intensity by 10.
Volcanic Explosively Index (VEI)
describes relatively size or magnitude of explosive volcanic eruptions
Scale 0-8.
Each increase in number increases intensity by 10.
volume of erupted material (e.g. ash fall, pyroclastic flows) height of eruption column, duration in hours and qualitative description terms)
Frequency
clear negative correlation (inverse relationship) between frequency and magnitude.
HICs will have extensive monitoring and education to adapt to these events. LICs however may use familiarity to breed contempt as locals become used to frequent eruptions.
Duration
Initial earthquake usually followed by massive aftershocks (Christchurch 2010)
Lahars are secondary impacts of volcanic eruptions that prolong impact and increase damage.
Landslides (St Helens avalanche) caused severe damage and 1.7km3 of material
Areal extent
Size of the area covered by hazard.
Lava flows travel 15kms
Pyroclastic flows 100km
tsunamis cover over 100km
Spatial concentration
Type of plate boundary and associated processes
Fault lines in Iranian desert city of Bam produces spring water, but a deadly earthquake hit in 2003 killing 80000
Eyjajallajokul in Iceland has extensive fertile soil from volcanic ash minerals, however its eruption in 2010 caused widespread aerospace disruption, over 100,000 flights cancelled
Volcanos occur along ocean ridges, continental rift valleys (Mt Kenya) subduction zones (Pacific ring of Fire) and over hotspots (Hawaiian island)
Earthquakes occur along plate boundaries, in particular convergent margins. (San Andreas fault) Also along old fault lines. (Shropshire fault)
Fracking also accused of causing earthquakes. 2017 South Korean earthquake hit less than 2km away from a geothermal and fracking site. Killed 70 people. China 2015 earthquake also close to a nuclear weapons site.
85% of earthquakes related to plate movements and their margins.
Speed of Onset
Gap theory
predicts likelihood and size of earthquake using past events as guideline. (Christchurch 11% chance)
Any large and longstanding gap is most likely to suffer future earthquakes.
The main shock and aftershock of the 1989 San Andreas Fault event occurred within the previous seismic gap.
Topography and Geology
bed rock, softer substances like sand and clay amplify seismic waves.
Type of boundary
Relief - if the land is prone to landslides or multihazard hot spots.