Latest News
May 2010 - Active Shear Zone in Southern Nevada
We combined GPS velocities and earthquake focal mechanisms to suggest that there exist a E-W trending sinistral shear zone in southern Nevada (Kreemer et al., 2010). This Pahranagat shear zone accommodates 2 mm/yr near the Nevada-Utah border and less to the west. The shear zone is a transfer zone between rigid crust to the north and diffusily extending crust to its south, and is a natural connection between the Wasatch fault zone and the Eastern California Shear Zone. 
May 2010 - Colorado Plateau Motion and Deformation
We analyzed data from continuous GPS sites in the Southwest U.S. and derived the very small motions relative to stable North America
(Kreemer et al., 2010). We show that the central part of the Plateau rotates as a rigid entity around a pole in the northern Rockies, but that the western and eastern margins of the plateaus show active extension.
April 2010 - Yucca Mountain Postseismic Relaxation
An study of GPS data from sites around Yucca Mountain, Nevada shows how postseismic relaxation from distant earthquakes can affect estimates of long-term strain rates
(Hammond et al., 2010). These effects can cause strain GPS rates to change over time, and have important implications for tectonic interpretation and seismic hazard analysis.
October 2009 - New Absolute Plate Motion Model
We just published a new absolute plate motion model (GSRM-APM-1) that is not derived
from hotspot data, but from an alignment of present-day surface motions
to mantle anisotropy orientations. You can find more information in
Kreemer (2009). The
figure below shows the GSRM-APM-1 velocities as well as Euler pole locations.
Figure Caption: (click on figure for higher resolution)
Vectors indicate velocity directions in the GSRM-APM-1 reference frame and color contours are the
velocity amplitudes. Stars are Euler pole locations (white, clockwise rotation;
grey, counterclockwise rotation).
Summer 2009 - New GGOS 2020 Book Has Been Published
The book "Global Geodetic Observing System: Meeting the Requirements of a Global Society on a Changing Planet in 2020" has been published by Springer. Hans-Peter Plag was one of the book's editors.
See http://www.springer.com/978-3-642-02686-7 for details, and/or order it at Amazon.com
March 2009 - New Publications
We have three papers just published in the new Geological Society of America Special Paper 447: Late Cenozoic Structure and Evolution of the Great Basin–Sierra Nevada Transition:Blewitt, G., C. Kreemer, and W.C. Hammond (2009). Geodetic observation of contemporary deformation in the northern Walker Lane: 1. Semipermanent GPS strategy, p. 1–15, doi: 10.1130/2009.2447(03). (link to GSA)
Kreemer C., G. Blewitt, and W.C. Hammond (2009). Geodetic constraints on contemporary deformation in the northern Walker Lane: 2. Velocity and strain rate tensor analysis, p. 17–31, doi: 10.1130/2009.2447(03). (link to GSA)
Hammond, W.C., C. Kreemer, and G. Blewitt (2009). Geodetic constraints on contemporary deformation in the northern Walker Lane: 3. Central Nevada seismic belt postseismic relaxation, p. 33–54, doi: 10.1130/2009.2447(03). (link to GSA)
Please contact the authors (Blewitt , Kreemer , Hammond) for details, reprints, etc.
Areal Changes in the Pacific-North America Plate Boundary Zone
New Publication: Corné Kreemer and Bill Hammond have used a large compilation of geodetic velocities in the Pacific-North America plate boundary zone to show that between the Gulf of California and the Queen Charlotte Islands the plate boundary undergoes no net areal change, consistent with being a transform plate boundary. They also showed that the area growth in the great Basin and Range is all offset by areal reduction in northern California above the southern Cascada subduction zone. This kinematic link is corroborated by independent geodynamic indicators and enforces the idea that the southern Cascade subduction zone may act as a 'window escape' for the Basin and Range material to flow/collapse towards. These results are now published in the journal Geology. The same journal issue also contains a comprehensive perspective of these results. Reprints are available upon request. 
Figure Caption: (click on figure for higher resolution)
A: Pacific-NorthAmerica (PA-NA) plate boundary zone in western North America in an oblique Mercator projection
around the PA-NA pole of rotation. North American model boundary is fixed, while the Pacific boundary is
constrained to move at the full PA-NA rate. The Sierra Nevada - Great Valley microplate (SNGV) and
Juan de Fuca plate (JdF) are modeled as rigid entities within the deforming grid. Black lines are Quaternary
faults. Colors indicate second invariant of strain rate tensor field. Grey arrows are interpolated model
velocities relative to North America. QCI, Queen Charlotte Islands.
B: Contours of the dilatational strain rates.
Red and blue colors indicate extension (i.e., area growth) and contraction (i.e., area reduction), respectively.
The gray lines divide the plate boundary into four zones (results for specific zones are published in article).
Dashed green lines are trajectories along (averaged) minimum principal stress observations for the greater
Basin and Range Provice (Humphreys and Coblentz, 2007).
2004 Sumatra Earthquake and Tsunami
New Publication: A team of researchers from NGL and Northwestern University have shown that highly precise GPS measurements may more quickly assess the danger of a tsunami by rapidly estimating the magnitude of large tsunamigetic earthquakes in near real-time.The results have been published as a cover story in Geophysical Research Letters. Click here for a PDF reprint. Click image for high-resolution figure.
Figure Caption: (above) Time series (blue lines) of east component of ground displacements after the great December 2004 Sumatra earthquake, recorded by continuous GPS sites in Southeast Asia.
The earthquake produced changes in site positions that are large enough to allow the magnitude of the earthquake to be assessed within 15 minutes, faster than was possible with seismic data alone.
This time interval is shorter than the time required by the tsunami to cross the Indian Ocean, illustrating that GPS data can contribute to tsunami warning by assessing whether an earthquake is large enough to generate an oceanwide tsunami.
The tsunami arrival times (color contours on map) are made available by NOAA Center for Tsunami Research (director: Dr. Frank Gonzalez).
The M=9.2 earthquake of 26 December 2004, near northern Sumatra, was the largest earthquake ever directly recorded with modern-day space geodesy. This earthquake and its subsequent tsunami caused immense loss of lifes and property around the Indian Ocean. Researchers of the Nevada Geodetic Laboratory have contributed to the understanding of this earthquake. They have also started to study the feasibility of using GPS in estimating the earthquake's magnitude and tsunami potential in real-time. These developments could be crucial for enhancing existing and future tsunami warning systems.
To your left you see a map of the eastern hemisphere. It shows in black arrows the horizontal displacements of
GPS positions during the earthquake. You can see, for instance, that at many thousands kilometers away from the epicenter
the Earth's surface moved with several millimeters. For instance, points in India moved approximately 1 cm to the east
during the earthquake. These displacements are measurable by averaging GPS positions for the days before and
after the earthquake. The offset
estimates can be used to quantify the earthquake's magnitude and the rough characteristics of the slip pattern during the
event. Our results, which have just been published,
agree with those obtained by other research groups.
The challenge we now face is two-fold. 1) Can we obtain reasonably accurate offset estimates using only minutes (instead of days/weeks) of data before and after the arrival of seismic waves at the GPS locations? 2) If GPS locations many thousand kilometers away from the epicenter moved, how can a stable global geodetic reference frame be maintained ?
