Charlie and secondary hazards from earthquakes and how to measure them

Earthquake magnitude

• this measures the amount of energy released at the epicentre

• MMS (moment magnitude scale) is accurate and better at measuring large earthquakes

• Measures total energy from 1 to infinity but stops at 10 usually

• Biggest was 9.5 in Chile 1960

Earthquake intensity

• An earthquakes Effect on people structures and the natural environment

• One scale is the modified mercalli intensity scale

• It takes observations from people who experienced the earthquake and puts them on a scale from one to 11

Ground shaking primary

• The horizontal vertical movement of the ground

• Severity of ground movement depends on the magnitude of the earthquake, the depth of the focus, geology, and the epicentre

Settlements that are close to the epicentre and if the geology is unconsolidated with a high water content It will experience more shaking.

• It triggers liquefaction and landslides

E.g. Nepal earthquake 2015 MMS of 7.8

Landslides/avalanches – Primary

• steep unstable slopes are notoriously vulnerable to landslides

• risk is increased by deforestation and heavy monsoon rains so that even small earthquakes can cause landslides

Nepal 2015 earthquake caused a landslide and avalanche on Mount Everest that killed 18 climbers

Soil Liquefaction- secondary

• water-saturated, sandy layers of earth act like liquids due to the pressure from earthquakes

• Open movement can make water penetrate the ground surface

• Soft sand can remain their structure

Christchurch New Zealand in 2011