Mountains Lecture 6- The Black Swan: why extreme events matter, and why they are hard to predict Flashcards
What is the definition of uniformitarianism?
The present is the key to the past
What is the history of uniformitarianism?
Theory grew from James Hutton’s geological observations.
However, was widely disseminated and popularised by Charles Lyell in his Principles of Geology (1830-1833).
What does uniformitarianism suggest?
Events we have experienced are representative of earths history.
We can take modern observations and knowledge surrounding them and infer something about past processes, conditions and events.
Name three events where there is no recent or historical analog.
Formation of the moon
Supervolcanoes and plateau basalt eruptions
Impacts and mass extinctions
What is neocatastrophism?
A view surrounding if large events with no modern analogue are important in Earth history
What do we need to know about to understand the role of catastrophic events?
- The distributions of events in terms of their size and frequency
- Their effectiveness, or ability to cause some change to the system
What can Earth events be described in terms of?
Magnitude and frequencies
When were the two large-magnitude Sumatra earthquakes?
26 December 2004 - 9.3
28 March 2005- 8.7
What was thr roung length of the Sumatra earthquake rupture?
Distance from Baltic Sea to Sicily
What did the 2005 Sumatra earthquake cause?
> 2m of permanent rock uplift in places and fundamentally altered the coastline.
How many earthquakes with a magnitude of 8 or higher occur annually?
3
How many earthquakes of 7-7.9 magnitude occur annually?
16
How many earthquakes of 6-6.9 magnitude occur annually?
140
How many earthquakes of 5-5.9 magnitude occur annually?
2047
How many earthquakes of 4-4.9 magnitude occur annually?
Around 13,000
How many earthquakes of 3-3.9 magnitude occur annually?
Around 130,000
How many earthquakes of 2-2.9 magnitude occur annually?
Around 1,300,000
What institution tracks and complies the number of ‘locatable’ earthquakes?
US National Earthquake Information Centre
Does the number of earthquakes vary much each year? Does the impact on human lives?
- No
- Yes
How many deaths for Sumatra earthquake?
298101
How many deaths for Haiti earthquake?
226050
What was magnitude of 2010 Haiti earthquake?
7.0
What is the only 8+ Mw earthquake to occur in 2019 and how many casualties?
Peru - 26th May
2 casualties
Discuss the 2011 Great Tohoku earthquake.
9 Mw
Japan
20896 deaths
Tsunami caused more deaths than the earthquake
Events led to Fukushima nuclear accident
Does a ‘cherry picking of results’ suggest evidence for earthquakes with high magnitude increasing?
Yes - clustering seen
If magnitude threshold changes then large earthquake occurrence seems largely random.
What are challenges of magnitude-frequency plots?
Number of small events are under-predicted as many are too hard to locate.
Cannot distinguish the number of magnitude 6-8 events
What is an alternative scale to a magnitude-frequency plot?
Using a logarithmic scale
How can frequency-magnitude plots help work out number of earthquakes of each magnitude?
Using a y-axis log scale can suggest that as we increase earthquake magnitude the number of events decreases - following a straight line.
What is the straight line equation?
y = n + mx
What is the equation to predict number of earthquakes of each magnitude using a straight line?
logN = a - bM
M= magnitude
N= number of earthquakes
a is intercept
b is slope
What is the relationship between frequency and magnitude called using a graph?
Gutenberg-Richter law (mid 20th century).
Can be defined for global, region or local datasets and can tell you expected number of earthquakes of a given size.
What is frequency of exceedance?
How often an event of at least that size is expected to occur
What is PGA?
Peak ground acceleration.
The maximum shaking in an earthquake, as a function of Earth’s gravity
What is predicting earthquake frequency-magnitude useful for?
Forcasting likelihood of future events and for understanding their effects.
Why may different regions or different parts of the same fault have different frequency-magnitude relationships?
Straight lines have different slopes (b values).
Therefore likelihood of specific magnitude events and relative numbers of big vs small events is therefore different.
What does a small b-value mean?
Large average earthquake size and proportionally more large events
What does a large b-value mean?
Smaller average earthquake size, and proportionally more small events
What can b values be used to calculate?
Daily earthquake probabilities.
Maps can show the likelihood of ground shaking with intensity.
Probabilities are not accurate predictions
Discuss the L’Aquilia earthquake
Italy
6th April 2009
6.3 Mw
309 deaths
Low-magnitude tremors (seismic swarms) leading up
No evacuation
Manslaughter charges
What is the difference between uniformitarianism and neocatastrophism?
Uniformitarianism suggests that events we have experienced are representative of Earth History.
Neocatastrophism is where large events – where there is no recent or historical analog – are thought to have had a profound impact on the evolution of the Earth system
What happened to Sumatra’s coast after the 2005 earthquakes?
Earthquakes caused >2m of permanent rock uplift in places – beach appeared to ‘rise’ out of the sea
Briefly (and in simple terms) describe how earthquake magnitude and impact for Earth varies over time.
The total number of earthquakes each year doesn’t vary that much over time. The number of deaths however can vary considerably
What is the Gutenberg-Richter law?
The relationship between the magnitude and total number of earthquakes in any given region and time interval
In earthquake frequency-magnitude plots what does it tell you if the b value is a) small and b) large?
Small b-value: large average earthquake size, and proportionally more large events.
Large b-value: smaller average earthquake size, and proportionally more small events.
What can trigger landslides in mountain environments?
Rainfall and earthquakes
Where is the asthenosphere located?
Upper mantle
What is an example of a divergent plate boundary?
Mid Atlantic Ridge
What is the process where the Earth’s surface moves up relative to another section due to earthquakes and movement along faults?
Tectonic rock uplift
In the earthquake cycle, what happens when the stress exceeds the local rock strength?
Earthquake
What parameters do you need to know to calculate the seismic moment of your earthquake?
Average slip of earthquake and fault area erupted
What is erosion?
The removal and transport of rock, soil or dissolved material
What is sediment load?
The mass of sediment leaving a catchment per unit time
What can the geochemical composition of sediment/sediment cores tell us about a mountain range?
Source area of sediment
Until 40 Myr ago, through which river did most of E Tibey drain through?
Red
What is ‘diffusive sediment transport’?
Independent grain movement under gravity
What characteristics might your mountain range have if it is composed of very sttrong rock?
High relief and steep hillslope gradients
How does that degree of rock exposure typically change with distance downstream?
Decrease
Frequency-magnitude plots are difficult to interpret as the raw data only is plotted. How might you transform the data to better show these relationships?
Transform frequency data to a logarithmic scale.
