Important Questions:

1

• Important Questions
• Inherited fabrics NE and NW older trends visible
  in Pre-C basement, but N trends established 700
  Ma (important for edge of CO plateau).
• What got reactivated? How important are inherited
  structures in future evolution? Where do the
  Pz-Mz terranes of central GB really start
  (isotopic boundaries quite variable)?
• Do we really know the profile of the base of
  crust despite one or two profiles from the 1980s
  (or 70s)?
• What is the relation between mantle velocity
  profiles and magmatic provinces? How has
  magmatism modified stress and structure?
• What is the cause of the thick band of continuous
  seismicity just east of the Wasatch front?

2
Does the eastern GB show non-uniform extensional
geometries like the S Sierra, or is extension
generally uniform? Why does the western
(Lahontan) depression have thin crust but little
apparent upper crustal extension, whereas the
eastern GB is apparently well extended? Is the
eastern GB undergoing magmatic underplating/
inflation in places? What can vertical components
of deformation measured (from GPS, in a global
ref frame) do to resolve differences? Fundamental
at end of Earthscope to know geometry of Sierran
and Wasatch fronts. Was this the Andes before
collapse?
3

• Solutions from Earthscope
• Fabric Mid-scale lithospheric thickness
  variations may represent earlier strength
  variations. Perhaps anisotropy can help answer it
  but, in the crust esp., its a geophysical
  challenge?
• Flexible array followup needed to trace deep
  geophysical structures toward the surface.
• Crustal Profiles We really do not know profile
  of the base of crust except in limited areas.
  Bigfoot receiver functions will be very valuable.
  Expensive to address with reflection and areas
  need to be prioritized.
• Margin seismicity, rifting Must establish mode
  of extension. Crustal thickness and rheology can
  determine contribution of GPE variation. Need
  better Eq locations to correlate seismicity with
  known faults or hidden detachments.

4

• Magmatic provinces Should expect some
  correspondence between interpreted inherited
  fabric (velocity) and magmatic history and
  compositions. Need more work on plutonic
  complexes to better define isotopic (Prot./Pal.)
  provinces for correlation to subregional scale
  deformation.
• General margin contrasts Despite some in the
  east, a big contrast in degree of shear in the
  west. 5-6 myr old in the west, so maybe two sides
  more similar at earlier times.
• -Need to try to strip Lt. Cz sedimentary fill to
  restore pre-extensional differences. Contour map
  of depth to graben basement from gravity, perhaps
  jointly with seismics. Interest in basin profiles
  in urban areas in east and west, and Yucca Mtn,
  w.r.t. shaking and seismic hazard.
• -Can combo experiments refute or verify contrast
  in extension/strike slip on the two sides of the
  GB?

5

• Magmatic inflation, fluid movement Vertical
  components of deformation (from GPS, in a global
  ref frame) together with attenuation/bright spot/
  conductivity structure.
• Self-Organization
• Need agency partnerships with common purpose to
  fund expensive active source surveys.
• Decide on an area to emphasize and determine
  which techniques will solve the questions.