Lecture index:

Key words and concepts:

• crevasse patterns in glaciers
• internal creep versus basal slip
• surges
• kinematic regimes of slumps
• gravitational collapse
• Sachung failures
• shutter ridges
• fault scarps
• sag ponds
• trenching
• Wasatch fault
• Meers fault
• Ventura avenue anticline
• GPS geodesy
• radar inferometry
• tectonic aneuryisms (blisters)

View of fault scarp created during 1983 Borah Peak earthquake (magnitude 7.3) in Idaho. Given the materail that supports the fault scarp - how long will the scarp last? Photo source: http://quake.usgs.gov/prepare/factsheets/Wasatch/FaultScarp.gif .

Many of these topics in this seciton are not usually considered as being neotectonic (e.g. glaciers and mass wasting). However, there is a grey zone (e.g. gravitational collapse), they are places where we can learn about deformational processes through direct observation, and this is a convenient place to put them.

Glaciers: A lot can be learned about deformation patterns from observing glacial form. Because of their lower rheidity this can be done in a human time frame. Additionally, glaciers show both shallow brittle features, and ductile deeper features.

Crevasse patterns:

• crevasses are simple tensile fractures.
• bergshrund (connection to detachment).
• marginal en echelon crevasses.
• internal ice streams.
• slab bending crevasses and stress.

USGS photo of crevasses on small alpine glacier. Photo source: http://www-atlas.usgs.gov/articles/government/IMAGES/usgs_shastina.gif .

Internal creep versus basal slip.

Glacial surges:

• the role of water.
• the role of calving and gradient changes.
• can tectonic surges happen?

Similar to glaciers, mass wasting features can be instructive as to deformation behavior.

• kinematic regimes of slumps.
• the Gulf Coast as a mega-slump
• behavior as a function of strain rate: creep to catastrophic failure.
  • frictional melts associated with catastrophic slides.

Related to mass wasting - these can be thought of as not so much as slope related, but as 'mound' related, and involving more pervasive deformation.

• ice caps
• Sachung failures.
• orogenic collapse.

The influence of topography and surface processes on tectonics?

• topography alters shallow stress field
• tectonic aneuryisms (tectonic blisters)
• segmentation?

For seismic risk assessment purposes, and for understanding deformation patterns from a uniformitarian perspective, it is useful to identify active faults.

How identified?

• associated geomorphic traits:
  • linear scarp
  • shutter ridge
  • sag ponds
  • springs
  • active versus fault traces delineated by differential erosion.
  • can be dependent on type of fault.
  • Wasatch fault in Utah as an example:

• offset geomorphic markers:
  • trenching.
  • streams along the San Andreas.
  • e.g. river terraces in New Zealand. - can yield horizontal and vertical components.
• changes in river gradient profiles (e.g. inexplicable knick points).
  • function or slip rate or frequency and rate of geomorphic response.
• first motion studies.

Meers fault in Oklahoma as an example: two well dated Late Holocene events. Presently seismically quiescent.

Since not so localized, these are more difficult to recognize. There is seismic risk associated with these.

Examples in Taiwan, California, Middle East

One of the better studied - Ventura Avenue Anticline in California.

Debate about supercedent and antecedent rivers that cut through anticlines.

With base stations and the right set up you can get a position accuracy of mm per year, well within the ability to detect year to year deformation.

Link to site describing GPS geodesy in Sumatra area.

Link to USGS site describing the technique of interferometry.

Ground movements associated with magma movement.

USGS article on using interferometry to track Yellowstone activity.

References:

Pinter, N., Johns, B., Little, B. Vestal, W. D., 2001, Fault-related Folding in California's Northern Channel Islands Documented by Rapid-Static GPS Positioning; GSA Today, 11, 4-9.