Earthquake hazards and impacts Flashcards
How many EQ’s are there globally every year and how many do they kill?
100,000 EQ’s and Kill 10’000
What are the different EQ waves?
P waves, S waves and L waves
What wave causes the greatest damage?
Love waves
What is used to measure seismic waves?
A Seismometer recorded on a seismograph
What is the order with which the waves arrive
- P waves
- S waves
- L waves
What two characteristics do Seismologists measure EQ’s
Magnitude (energy) and Intensity (Impacts)
What is EQ magnitude measured in?
The Moment Magnitude Scale (MMS)
What does the MMS scale measure?
Energy released at the epicentre at the seismic moment
Describe the scale of the MMS
Starts at 1 and is infinite (the largest was in Chile in 1960 at 9.5). It is logarithmic e.g. MMS 9 = 32 x MMS 8
Somerset 2019
MMS 3.2 - Resident reported house rattled
Chile 1960
MMS 9.5 - Largest EQ ever recorded - 2 billion times more energy than Somerset 2019
What does EQ intensity refer to?
Refers to the impacts on Landscape, Infrastructure and people
What does the Mercalli Intensity Scale (MIS) use?
Uses witness observation to rate the EQ
What is the range of the (MIS)?
Ranges from I (hardly noticed) to XII (catastrophic)
What level was the Chile 1960 EQ on the MIS
XII - Total destruction
What are Primary EQ hazards?
Hazards directly caused by the EQ and occur during the EQ
What are Secondary EQ hazards?
Hazards indirectly causes by the EQ (knock on effects of the primary hazards) and can occur during or after the EQ
The Loma Prieta 1989 EQ (Effect of geology)
MMS 6.9 EQ - The city’s Marina district was built on man-made landfill which resulted in Liquefaction causing buildings to collapse
What are Aftershocks?
Smaller EQ’s triggered by the mainshock which can take place seconds or years after the original EQ due to the plates “settling down again” and can be more deadly than the mainshock
What happened in Christchurch in 2011
An aftershock where the epicentre was closer to the city and the infrastructure was already weakened
Why would EQ prediction be good?
It could save lives through evacuation however it is not fully possible yet
What EQ prediction is possible now?
The arrival of deadly L waves can be predicted seconds / minutes before they hit when the P waves arrive, this can give much needed time for evacuation etc
What is EQ forecasting?
Determines the probability for a place to experience an EQ
How is EQ forecasting possible?
It is possible by looking at the tectonic setting and past EQ’s
Why do 95% of EQ’s occur at plate boundaries?
Friction occurs and stress builds as plates try to move, eventually the stress overcomes the friction resulting in sudden plate movement as energy is released as seismic waves
What are Intra-plate EQ’s?
They occur within plates, some occur at hot spots
What is a hot spot?
Where a mantle plume underlies a plate and melts through the lithosphere and seismic energy is released
What is an example of a hot spot?
Hawaii is a hot spot in the middle of the pacific plate 3000km from the nearest plate boundary
What can also cause Intra-plate EQ’s other than hotspots?
other EQ’s can occur at ancient faults where there are fractures in the lithosphere which are reactivated by stress, however this is poorly understood
What is an example of an ancient fault?
New Madrid in Missouri 1811-12
