CRUST 2.0

A New Global Crustal Model at 2x2 Degrees

Gabi Laske, Guy Masters and Christine Reif

UPDATE (July 15, 13): CRUST1.0 is now released. Please go to the CRUST1.0 webpage. We no longer update CRUST2.0 and related services. The page remains open but we discourage usage of this model.

UPDATE (April 13, 12): We are currently modifying our CRUST1.0 proto-type model after testing revealed some inconsistencies with recent surface wave data.
We are modifying the model and expect release by August 2012
UPDATE (March 17, 11): Global average, average continental profile and average oceanic profile are given below.
UPDATE (March 09, 11): Google Earth kmz file available for crustal thickness. Go down to download section.

UPDATE (September 06, 10): The anonymous ftp site for the model was moved. The links to individual files of the model should now work again. The link to the tar file was not affected.

IMPORTANT NOTICE

We no longer update and provide support for this model! Please use CRUST1.0 instead.
(August, 2013)

Description of the model

This model is an updated version of CRUST 5.1. This new model is specified on a 2x2 degree grid and takes advantage of our recent compilation of global sediment thickness which is defined on a 1x1 degree grid. We also compiled ice thickness on the same scale. The new crustal model also takes advantage of our still ongoing effort to compile crustal thickness on a 1x1 degree scale. Our current compilation covers most of Eurasia, North America, Australia and some areas of Africa and South America and in the oceans.

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. Starting with CRUST5.1 cells in CRUST2.0 were adjusted in type to better reflect the edges of shelves and the coastline. Adjustments have been made in some tectonic regions in the Americas and Eurasia (especially around the orogenic belts). Adjustments to the ice thickness were also made in each cell and is now within 250m of the true ice thickness. Sediment thicknesses in each cell are to within 1.0 km of the true sediment thickness and crustal thickness are within 5 km of the true crustal thickness.
Bathymetry and topography is that of ETOPO5.

The 2x2 degree model is composed of 360 key 1d-profiles (compared to 139 of CRUST5.1) where one of these profiles is assigned to each 2 x 2 degree cell.
Each individual profile is a 7 layer 1D-model with

ice
water
soft sediments
hard sediments
upper crust
middle crust
lower crust

Parameters VP, VS and rho are given explicitly for these 7 layers as well as the mantle below the Moho.

Global, Continental and Oceanic average

some applications require the accurate knowledge of the spherical average of Earth's crust. In the file given here, we provide the global average profile (spherical average) and the average profiles for continental and oceanic crust. All averages were obtained using equal-area weighting so the global average is the true spherical average (the c-00 term in a spherical harmonic expansion) and not the average of the 2x2 cells! Note several differences of the global average to reference model PREM (Dziewonski and Anderson, 1981):

the crustal thickness is less by 2.58km
the average water depth is less by 0.38 km
Vp for water is 1.50 km/s, not 1.45 km/s (the latter applies to high latitudes)

show averages

PREM reference: Dziewonski, A.M. and Anderson, D.L., 1981. Preliminary reference Earth model. Phys. Earth Planet. Int., 25, 297-356.

Why do we need yet another 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 5x5 degree model CRUST5.1 is no longer accurate enough. We have therefore begun to expand our database on crustal information (refraction, reflection seismics as well as receiver function studies). The new model CRUST2.0 is a prototype 2 degree crustal model and will get adjusted as our database increases.

What makes CRUST5.1/CRUST2.0 so special?

Our crustal models differs from previous models in that:

The thickness and seismic/density structure of sedimentary basins is accounted for more completely.
The velocity structure of sedimentary basins is estimated using a significantly larger database of crustal structure.
The compressional wave, shear wave, and density structure have been explicitly specified using newly available constraints from field and laboratory studies.
The use of statistics to predict crustal structure in areas without field measurements. The velocity structure of the crystalline crust and uppermost mantle is estimated from the statistical average of regions with a similar crustal age and tectonic setting.
The model is extremely transportable. The files provided are small ASCII files. The files are not compressed. We also provide Fortran 77 computer code to read the models.

Reference:

Please refer to the REM web site if you use this model: http://igppweb.ucsd.edu/~gabi/rem.html
or
Bassin, C., Laske, G. and Masters, G., The Current Limits of Resolution for Surface Wave Tomography in North America, EOS Trans AGU, 81, F897, 2000.

A description of CRUST 5.1 can be found in: Mooney, Laske and Masters, Crust 5.1: a global crustal model at 5x5 degrees, JGR, 103, 727-747, 1998.

Download section:

The model and Fortran source code to read it is available here. The Fortran source code should compile with any Fortran 77 compiler. To get access to the README or download individual files, Click here. To download a compressed tar file with everything included (use gzip to uncompress) Click here.

CRUST 2.0 GOOGLE EARTH KMZ FILES

crustal thickness

Go back to
REM page
REM Crust page

Gabi Laske ( glaske@ucsd.edu)

Gabi's home page