Fault Displacement Markers

1. Coseismic Displacement

Timescale: few seconds i.e. info about fault displacement over a few seconds

Data: Interferograms

Interferometry

Technique:

Superposition of waves causes interference

Information is extracted from the resulting interference pattern

Seismic interferometry

Utilises cross correlation of signal pairs

To reconstruct impulse response of a given media

Intensity
Pattern

= f ( phases difference between 2 waves which combine )

If waves are:

In Phase - undergo constructive interference

Out of phase - undergo destructive interference

Not in/out of phase - intermediate intensity pattern

Used to determine relative phase difference

Interferograms represent displacement

Method

Elevation measured with satellite data

Difference btwn 2 images yields displacement
i.e. elevation change from before to after earthquake

L'Aquila Interferograms

Obserrved data

L'Aquila Earthquake 2009

SW dipping normal faults

Mw 6.3, slip ~0.6-0.8 m

Confirmed still cannot predict earthquakes

Scientists accused of being too optimistic / reassuring

Many daeths as people did not evacuate

= interferograms measured by
differencing radar imagery from before & after

Modelled data

To recreate observed displacements

Seeks to understand seismicity / dynamics of fault

2. Interseismic Displacement

Timescale: years to decades

Data: GPS-derived horizontal velocities i.e. interseismic displacement

Method

  1. Detect displacement @ GPS stations over long period
  1. Observe relative displacement of different pts across area of interest as f (time)

Appenines
Horiz Velocities

  1. Moving South displacement increases & rotates to N

Reflects rotation of subduction zone @ rates of 5 mm/yr

2. East Appenines moving faster than West

Velocities higher on E Appenines

Evinces extension - Appenines are being stretched

3. Postglacial Fault Scarps

Timescale: kyr to tens kyr

Fault scarp = sharp contrast btwn bedrock & debris on hillside

e.g. Magnolia fault scarp, Central Appenines

Uplifted block (hanging wall) sits above
Pleistocene sediment (deposited colluvium)

Fault scarp formation

Glacial Max

Lotsa sediment produced

∴ Fault scarps not preserved--> since degradation so rapid

V efficient hillslope processes

Postglacial

Less efficient hillslope processes

∴ Fault displacement = preserved & exposed

Scarp visible represents uplift since 18 kyr (LGM)

Measuring
fault scarps

  1. Cosmogenic nuclide dating
    of fault scarp exposure
  1. Extent of fault scarps

amount of displacement over 18 ka

offset ~ size of scarp

confirm age ?

Findings

Offset msmts on fault scarps across Appenines

Agree with fault linkage theory

Displacement greatest in middle of faults

fault segments in array centre displaced > tips