GLOBAL STRAIN RATE MAPS
W. Holt, Chairman
A. J. Haines, Vice-Chairman
G. Blewitt, Vice-Chairman
The mission of this ILP Project is to determine a globally self-consistent strain rate and velocity field model that explains geodetic and geologic observations. The overall mission also includes:
contributions of global, regional, and local models by individual researchers; such models are useful to the community for studies of dynamics and for quantifying seismic hazards;
archiving existing data sets of geologic, geodetic and seismic information that can contribute toward a greater understanding of strain phenomena;
archiving existing methods for modeling strain rates and strain transients.
The website for this project is presently being maintained by Chuck Meertens at UNAVCO:
The decision was made to place the website at UNAVCO, because this is the location of results from GPSVEL (a project guided by Geoff Blewitt), a project designed to provide a self-consistent GPS velocity field that includes data from research groups around the globe.
Strain Rate Models
On just about any scale, there are at least four types of strain rate model: (1) models of strain accumulation inferred from geodetic data, (2) long-term strain rates inferred from Quaternary fault slip rates, (3) strain rates related to earthquakes, and (4) strain transients associated with post-seismic phenomena. No single model can accommodate all four types of phenomena. It may be necessary to mix data types in cases for which geologic or geodetic observations are sparse or lacking. In such scenarios, some sacrifice in model resolution must be made.
There are at least 3 identified model types.
1. Master global models
2. Regional models
3. Local models
Master Global Models
A “master global model’’ usually contains a mixture of both geologic and geodetic information. Currently, it is not possible to have a high resolution global model of strain rate that includes both narrow and diffuse zones of deformation (plus plate velocities) without incorporating both geodetic and geologic information. In other words, current geologic fault-slip rate information is not sufficient to have a strictly ”long-term’’ model on a global scale. Neither are geodetic data within diffuse zones of deformation dense enough to define strain rates within all regions. Thus, some compromise in resolution must be made by combining data types. Modeling indicates that over spatial smoothing scales of 50 - 300 km, deformation fields inferred from geodetic data merge with those estimated from geologic data. The present spatial resolution limit for a global model of strain rate may be of this order. One or more methodologies can be used to construct a self-consistent master model. It is envisioned that high-resolution results from individual research groups will be built into a global master model. In practice, a number of global models could be attempted. For example, the Steering Committee has suggested that global models might have plate motion models built into them (e.g. NUVEL-1A, GPSVEL, or other recently derived models).
Since most interest exists in the details, regional models may be the most useful component of the ILP strain rate project. Regional models may involve estimates of strain accumulation inferred from geodetic observations, long-term strain rates deduced from geologic information, as well as strains released by earthquakes using catalog information. Regional models may also be based on post-glacial rebound studies. A number of research groups have different approaches for inferring active deformation fields from observations. Steering Committee members have recommended that all results from the different approaches should be considered. These different methodologies and results can be archived. Full credit and citation will be given to the authors from the contributing research group(s). We envision that a number of high resolution results for plate boundary zones can be built-up over time.
Local (fault scale) models are most likely to be based on studies of post-seismic relaxation phenomena (e.g. as derived from GPS and InSAR observations). A number of discussions at Steering Committee meetings have centered around the inherent differences between 2-D and 3-D models, elastic versus plastic, strain transients, long-term (geologic) strain, etc. Some effort should be dedicated to investigating these issues. A consensus on how these will be handled in the Global Strain Rate Map project has not been reached. However, all agreed that there are different types of observations that reflect different length- and time-scales. There are also a large variety of model approximations; no single model can deal with the different spatial and temporal phenomena. Additional discussion is needed on where the primary focus should be. Perhaps, a master global model, as well as a number of regional models, can focus on estimates of the long-term steady-state strain-rate fields. There could also be a number of 3-D models that address observations at subduction zones, post-seismic deformation, etc.
For further information please contact:
Dr. W. E. Holt, Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794-2100, USA; Tel.:516 632 8215; Fax: 516 632 8240; e-mail: email@example.com
Dr. A. J. Haines, University of Cambridge, Bullard Laboratories, Madingley Road, Cambridge CB3 OEZ, UK; Tel.: 0044 1223 337 101; Fax: 004 1223 360 779; e-mail: firstname.lastname@example.org
Dr. G. Blewitt, University of Nevada, M. S. 178 Reno, Nevada 89557-0088, Tel.: 775-784-6691 ext. 171, FAX; 775-784-1709, e-mail: email@example.com
International Lithosphere Program
http://www.unavco.ucar.edu/science_tech ... strn1.html