CRUST 1.0

A New Global Crustal Model at 1x1 Degrees

Gabi Laske, Zhitu Ma, Guy Masters and Michael Pasyanos (LLNL)

Description of the model

This new model is specified on a 1x1 degree grid and incorporates an updated version of our global sediment thickness .

Bathymetry and topography is that of ETOPO1 that can be downloaded at NOAA's NGDC.
ETOPO1 is a 1-arc minute model of Earth's global relief, including surface topography and seafloor bathymetry. In ice-covered regions, "ice surface" and "bedrock" are given. From the ETOPO1 files, we derived topography, bathymetry and ice thickness in our new model by binning and averaging the ETOPO1 data in 1-degree cells.

The global crustal models CRUST5.1 and CRUST2.0 use type keys to assign various types of crustal structure (such as Archean, early Proterozoic, rifts etc.) in each cell. In both these models, the crustal types were also used to assign ice, sediment and crustal thickness.

In CRUST1.0, the principal crustal types are adopted from CRUST5.1. But the crustal types are now aligned with the crustal age map of Artemieva and Mooney. Additional crustal types mark specific tectonic settings, such as orogens, continental rifts, continental shelves and oceanic plateaus. CRUST1.0 also has a few new types, including one for very young (< 3 Myrs) oceans. In contrast to older models, the function of crustal types in CRUST1.0 is limited to assigning elastic parameters to layers in the crystalline crust.

CRUST1.0 will consist of less than 40 crustal types. Each of the 1x1-degree cells will have a unique 8-layer crustal profile where the layers are

1. water
2. ice
3. upper sediments
4. middle sediments
5. lower sediments
6. upper crust
7. middle crust
8. lower crust

Global, Continental and Oceanic average

TBD

Why do we need an accurate crustal model?

Seismic tomography has been extensively used in various forms to determine the three-dimensional velocity structure of the Earth's mantle. The data used in these studies are surface wave (waveforms and dispersion measurements) and free oscillation (frequency shift) data as well as body wave travel times (arrival times from catalogues such as the ISC catalog and specially hand-picked long-period arrivals). For the majority of these studies, the crust has a significant impact on the observed seismic data but, at the same time, is too thin to be resolved by them. Most authors handle this by applying an assumed "crustal correction" to the data before an inversion for mantle structure. Since the inversion techniques can erroneously map crustal structure down to great depth (at least 250km), accurate crustal corrections to the data sets are extremely important.

Another aspect is the seismic monitoring of nuclear explosions. Key elements of the monitoring effort are location and size estimation. The location accuracy strongly depends on the chosen velocity model (i.e. crustal structure), especially when seismic sources lie outside the monitoring network.
Monitoring on regional scale includes the modelling of short-period surface waves and the propagation of Lg waves which are very sensitive to variations of crustal structure. Obviously, an accurate image of the Earth's crust would tremendously improve the understanding of wave propagation of such phases. With the volume of datasets and the demand on resolving small-scale structures increasing, we found that the 2x2 degree model CRUST2.0 is no longer accurate enough.

---

Updates:

27 August 2013

The assignment of the continent/ocean boundary, was still loosely coupled to crustal types. In 136 cells along the coast, this erroneously led to the omission of water. The crustal profile then started below sea level after the bathymetry in ETOPO1 was added. In 7 cells, this meant a shift of 500 to 1140 m (see affected areas in the plot on the right). We now add ETOPO1 directly into the model (see below under downloads). Three areas are forced to NOT have water even though they are below sea level: Caspian Depression (several cells), Qattara Depression in Egypt (1 cell), Lake Eyre in Australia (1 cell). NB: The Dead Sea and Death Valley are both surrounded by high topography and therefore do not show up in CRUST1.0 as depressions. The consequence of this change is that some costal areas now appear to be flooded even though the majority of the area within a 1-degree cell is land. This is because the average topography is negative. The change is minor, and we retain the name and version of the model.

• Compressed xyz file of total crustal thickness (excl. water): click here
• Compressed xyz file of depth to Moho (with resp. to sea level): click here
• Compressed xyz file of sediment thickness (in km): click here
• Compressed xyz file of sediment thickness (in meters): click here

Other References:

Links to older models CRUST5.1 and CRUST2.0

External links:

20 August 2013: A group at the Sandia and Los Alamos National Laboratories develop 3D tomographic models of the crust and mantle. As part of this, the group developed a model parameterization on software support library for 3D Earth models. Their software distribution now includes CRUST1.0. Please find more info at their GEOTESS website at www.sandia.gov/geotess.

LLNL-G3Dv3
Reference: Simmons, N.A, S.C. Myers, G. Johannesson and E. Matzel (2012), LLNL-G3Dv3: Global P wave tomography model for improved regional and teleseismic travel time prediction, J. Geophys. Res., 117, http://dx.doi.org/10.1029/2012JB009525.
Link: Download the LLNL-G3D model from the IRIS website: http://www.iris.edu/dms/products/emc-llnl-g3dv3

Funding:

This research has been fully or partially funded through the following NSF grants: EAR-03-36864; EAR-12-15542; EAR-14-15763