Disciplinary Groups: Geophysics

Moderator: Del Bohnenstiehl; Co-moderator: Laurent Montesi

Participants (list your name here):
Del Bohnenstiehl
Spahr Webb
Laurent Montesi
Danielle Stroup
Tim Crone
William Wilcock
Robert Weekly
J. Pablo Canales
Helene Carton
Maya Tolstoy

CROSS ISS DATASETS
Table shows which data has been collected. During the breakout session we will discuss missing datasets and those not available through the marine-geo data portal. Colored data is not available through data portal! to the best of our knowledge!

Question: At what point of the processing sequence should the data be released.

Answer: Any step, just mention what you've done (add to metadata) (and have publication)

LIST OF QUESTIONS ADDRESSED BY GEOPHYSICISTS

This list is meant to be completed and worked on during the discussion. We identified a few questions for which Geophysics helps providing an answer. For each, we identify observational and theoretical methods commonly used. It would be useful to complement this draft with specific results. Finally, the goal is to identify topics for which synthesis paper could be written.

Do no hesitate to modify this draft!

1 What kind of questions do geophysicists address?
Complementary approaches of observations and modeling
Seismology is not everything: magnetics, gravity, sonar, etc.

2 What is the state of the mantle underneath mid-ocean ridges?
Note only snapshot attempts; at that large scale, do we expect any variations over decades (maybe in magma extraction plumbing). If so, where should we check?
Origin of Ridge segmentation
Techniques/datasets; Still collecting
Results

Temperature and melting
Techniques
Seismic tomographic images, EM images, gravity (assuming we know the crust), compliance
Mantle flow model coupled with melt production (chemistry) and migration
Pn/Undershoot at each of the three sites;
Main results: many from MELTS, type to synthesis ISS results?
GRavity for mantle: need to wait for better crust information before I&S possible
Low melt fraction indicating efficient melt extraction
High resistivity indicate dry mantle
Focused magma-rich region underneath ridge
Melt accumulation below the crust (compliance, reflectors); Compare EPR and JdFR, look at lower spreading rate?
Mantle flow
Technique
Seismic anisotropy (Pn, splitting); Lau and Endeavour just collected
Modeling of flow field, strain
Result
Toomey’s “misaligned” anisotropy. Under fire. Equivalent experiments elsewhere? Interest to do at lower spreading rate?

3 What is the structure of the crust?
May be able to detect time variation based on the eruption cycle. Is that checked anywhere?
Physical state
Techniques
Tomography.
EM
Gravity anomaly (with mantle model)
Thermal model
Results
Variations of crustal thickness
Variations in layer 2A
Is the length scale and amplitude of variations similar at every ridge?
Gravity available at all three sites
uppermost crust (MCS): Done for Endeavour; Lau (Scripps not published, Dunn just collected). EPR: old dataset. Too old to make good comparison. Would be nice to do 3D MCS @ Lau.
Deformation
Techniques
Seismicity is king! Microseismicity, hydroacoustic
Elastic fault interaction modeling
Results

Comparing microseismicity EPR/Endeavour (just got funding); Similar scale.
can we have moment tensors at each sites? EPR: events too small; Endeavour, tried, not so succesful

Note: Gap on vent-scale seismicity at Lau

4 How are fluids moving through the crust
Fundamentally time-dependent problem handled either through repeated snapshots or rate-sensitive data
Note that geophysics is the most direct indicator of subsurface processes
Hydrothermal flux
Techniques
Microseismicity, hydroacoustic
Near-bottom magnetics
Porous flow modeling; link with chemistry
Results
Correlation between seismicity and vent distribution (Deb Kelley's talk) Two sites
Burn holes (JdF only)
Permeability estimates from seismicity at EPR and Endeavour + TAG.
Magmatic flux
Techniques
Microseismicity, hydroacoustic
Near-bottom gravity
Eruption modeling; dike emplacement and flow; degassing
Lava flow modeling
Results
Dike emplacement BEM only at Endeavour

5 On which of these questions has there enough progress being made for a cross-ISS comparison (synthesis paper)?
Pn/Undershoot at each of the three sites;
Gravity available at all three sites; can do crustal structure
Correlation between seismicity and vent distribution at least Endeavour and EPR
Permeability estimates from seismicity at EPR, Endeavour + TAG

Special volume; There's the EPR G3; Not Geophysics on its own, but could participate to a "Cross-ISS" general special issue. G3 special issue preferred because of the long time span.

6 What comparison can be made with new analysis of existing dataset?
Properties of magma chamber
Modeling of fluid flow at EPR
Model flow and temperature of the mantle at all ISS
Model thermal structure of the crust, magma chamber, at all ISS (revisit with T, stress dep viscosity)

7 What critical datasets are missing to enable I&S?
Integrate heat flow at EPR to complement existing Endeavour (not yet published) data.

8 What non-I&S should be brought into the synthesis?
Hydroacoustic earthquake location @SWIR
Reykjanes microseismicity + MCS, mantle tomography + 1D
Gulf of California seismicity + MCS.
Mid-Atlantic Ridge; microseismicity (TAG), tomography @ 35°N, Lucky Strike (active source + microseismicity)
hydroacoustic data from ??? Straits (Del)
Marianas backarc active sources (Japanese + Greg Moore); includes mantle component and OBS
Seismic data (MCS, OBS) of Galapagos Spreading Center
EPR MELTS

Discussion topics (list ideas and suggestions here):
    •    What are the problems that can be approached by cross-ISS comparison within your discipline?
    •    Are there disciplinary collaborations that could integrate existing data sets?
    •    Could a review be written about fundamental advances in your discipline?
    •    Would a special volume within a disciplinary journal be a useful venue to showcase Ridge 2000-related research in your discipline?
    •    What data has been collected or analyzed and not submitted to the Data Portal?