Tectonic geomorphology Flashcards
What is important to consider when looking at tectonic geomorphology?
Time scale
What does a strainmeter measure?
Strain over time
Finding the long term trend of what is critical?
Long term trend of deformation rates
What do slip rates give an idea of?
Time scale
What can subduction cause?
Severe earthquakes
What is needed to date features?
Well defined markers
How can you identify a young fluvial terrace?
Young terraces aren’t deformed
How can you identify older fluvial terraces?
They have shifted along
What happens to a river if a fault activates?
The river becomes disrupted
Why does Faults Propagation need to be implemented?
In an active fault segment, the deformation rate varies so fault zones have varied seismic behaviours
What is the theory behind the earthquake cycle?
The size of an earthquake depends upon the amount of time since the previous earthquake
Explain the uniform earthquake model
Taking into account fault segmentation, the slip-at-point is constant which means that small catch up events are needed
What is the slip-at-point?
It is constant on a central “simple” segment with more complex geometry
Explain the variable slip model
Slip-at-point varies from event to event, it is random and there is no pattern
What are along-fault variations in slip distribution not filled with?
They are not filled with catch up events but reflect variations in long-term slip rate along the fault and or segmentation of the fault zone
What are short term data within?
The seismic cycle (2-3 ka)
Give 4 examples of data that can be used to quantify deformations
Seismological data
Paleoseismology data
Geodesy
Historical data
What are two issues with short term data?
Variable by faults
Variable with distribution of population today and in the past
What does long-term data do?
Average the seismic cycle (2-100ka)
What are 3 types of long term data for quantifying deformations?
Tectonic geomorphology
Morphochromology
Average quaternary slip rate
What is the rate equation?
Rate = distance / time
What is rate?
This is the slope of the linear regression between terrace ages and their offsets
What two things are needed to estimate the general trend of slip-rate estimates from goemorphologic evidence?
Well-defined and well-preserved geomorphic offset markers
Datable markers
Give 4 examples of geomorphic offset markers
Fluvial terraces
Alluvial fans
Moraines
Outwash, channel
How do fluvial terraces work?
Emplacement of a terrace at the time of a large sedimentary discharge which buries the fault. After some energetic discharge the stream incises the channel and the original terrace is abandoned and begins to record faulting, but the riser is constantly refreshed by lateral cutting. During a new episode of entrenchment the terrace is abandoned and there is now a passive marker between this terrace and the original which records lateral displacement.
What is an issue with river terraces?
All episodes may not be recorded by all rivers and older terraces can be eroded by further incision
What can be used to determine the rates of slip, uplift and shortening?
Vertical offsets, ages and fault geometry
What 3 things show evolution of a normal fault?
Triangular facets
Perched valleys
Sinuosity of mountain front
What 6 tools are there that can be used for dating?
Field and imagery analysis Qualitative and quantitative mapping Digital Elevation Motion(DEM) Geochronology Syntheses Physical modeling
The rates of what 7 things can be found from morphochronology?
Deformation Uplift Erosion Incision Deglaciation Glaciation
What are 6 morphochronological dating techniques?
Lichenometry Carbonate coatings Radio carbon dating Luminescence Cosmogenic nuclide dating U-Th/He
How does lichenometry work?
Lichen growth determines the age of the exposed rock
What is a requirement for lichenometry?
Local calibration curve
What are the issues with lichenometry?
Delay between exposure and calibration curve
Varying growth rates from region to region
Growth rates may vary over time
Short historical timescale
What is the timescale for lichenometry?
400 years
What are carbonate coatings?
Pedogenic carbonate is amenable to uranium-series dating, such dates provide estimates o the age of the host rock and
paleoclimate proxy records contained in the carbonate itself
What are the requirements for carbonate coatings?
Local calibration curve
What are the problems with carbonate coatings?
Delay between host and exposure and coating development
Varying growth rates that vary over time
What is the timescale for carbonate coatings?
Less than 0.5 Ma late pleistocene holocene
What is radiocarbon dating?
A radiometric dating method that uses the naturally occurring radioisotope carbon 14 to determine the age of carbonaceous materials
How far back does radiocarbon dating go?
Up to about 60,000 years
Explain radiocarbon calibration
Calibration curve shows radiocarbon age vs calendar years, there is then a range of possible calendar ranges
When can dendrochronology calibration be done up to?
11ka
When can U/Th calibration be done up until?
45ka
What are 4 methods of morphochronology?
Radiocarbon dating
Thermo luminescence (OSL)
Cosmogenic nuclide dating
U-Th/He
How does cosmogenic isotope dating work?
Cosmic rays hit targets to produce products
Explain the altitude dependence
Attenuation through the atmosphere
Explain the latitude dependence
The Earth’s magnetic field deflects the charged particles of the cosmic ray flux
How does quantitative morphology work?
Measure the offsets by matching piercing points on both sides of the fault
What happens if there is lots of soft sediment?
There are more layers
What is an issue with radiocarbon dating?
Difficult to find materials that can be radiocarbon dated
Give two examples of materials that can be radiocarbon dated?
Charcoal and some shells
What element is used for cosmogenic isotope dating?
This is non-atmospheric CO2 or an element that is not contained in the rock
What increases the production rate?
Higher latitudes and altitudes have higher production rates
