REM Workshop

Summary of the La Jolla Workshop

A workshop has been held May15-17, 1997 at IGPP, La Jolla, to discuss several aspects of a new reference Earth model. We agreed that the new reference earth model should not just be a 'tweak to PREM'. We regard this process as a community effort with input necessary from the wide range of possible users (e.g. mineral physicists and geodynamicists) and not just seismologists. The workshop format was based on a Plume conference format with a few (mainly non-seismological) review papers interspersed with sessions of short representations and discussion. There were also 25 posters to stimulate discussion outside of the main lecture hall. Review talks were the following:

S. Karato: The three "an"s and the reference Earth model: Anelasticity, Anisotropy and Anharmonicity and Earth structure
D. Weidner: On mantle materials and mineral physics with emphasis on phase transformations and transition zone
J. Mitrovica: On flow calculations in the mantle and determination of viscosity (large-scale structure in the mantle)
R. Jeanloz: On the core and core/mantle interactions
G. Nolet: What do seismic waves really resolve in an isotropic 3D Earth?

In a plenary discussion at the end of the workshop, the participants agreed to recommend the following guide lines.

These guide lines are preliminary and open for discussion. Please contact us ( gmasters@ucsd.edu) if you feel that an important issue has not been addressed.

What should we have soon?

Availability of REM guidelines, datasets, and codes on a REM website
Recommendations as to the scope of a REM (explicit recommendations as to what parameters, what parameterization(s), what specific datasets, and what specific codes should be used in the REM - at least for the 1D part)

This is what this website is all about. A preliminary version of Exchange Format Specifications have been summarized by Pete Davis and is open for discussion.

The Holy Grail: What do we expect from a new REM?

It should be an internally consistent dynamical, chemical, mineralogical model of the Earth predicting:

seismology (tomography, anisotropy, attenuation,etc)
gravity/geoid, post-glaical rebound, etc
topography of all boundaries, heat flow, magnetic field, etc

How many REMs do we need?

There should be:

a global 1-D REM
regional 1-D REMs (ultimately tied in to a global 3-D model)
a ''regionalized'' and ''a-priori'' model of the top 100/200/300(??)km of the Earth
a full 3-D global model

Examples of Seismological Guidelines

All REMs should:

be at least density, elastic moduli, and attenuation (or equivalent)
specify structure throughout the Earth (from center to surface)
have a sufficiently flecible representation of attenuation to allow datasets at different frequencies to be mixed (e.g. an absorption band operator with Q a function of frequency in the band and with corner frequencies that can be spatially varying).
have an associated ''error analysis'' (e.g. corridor of possible models?)

Some Recommendations for Specific Regions

CRUST

Existing models should be improved using short period surface wave data
Attenuation should be included
Perhaps include anisotropy?

UPPER MANTLE AND TRANSITION ZONE

1-D models should be transversely isotropic (TI in all solid regions?)
The only ''global'' discontinuities should be 410 and 660
Define the global discontinuities by width and shape

LOWER MANTLE

As close to Adams-Williamson as possible (taking account of attenuation)
Maybe only isotropic?
D" should usually be distinguished by a second order discontinuity (at what depth?)

OUTER CORE

Isotropic(?), homogeneous, and as close to Adams-Williamson as possible

INNER CORE

Should 1-D model be isoptropic?
Should ICB be simple first-order discontinuity (or define width and shape)?
Should a ''simple'' anisotropic model be provided?

The next meeting is planned to be held at Harvard University late 1998/ early 1999.

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Gabi Laske ( glaske@ucsd.edu)