|
May 26 2005
IGPP Professor T Guy Masters elected to the Royal Society
Today IGPP Professor T. Guy Masters was elected to the Royal Society.
The Royal Society is Great Britain's most prestigious scientific body. This
honor reflects the outstanding contributions Dr. Masters has made to
low-frequency seismology, elucidating the large-scale structure of the
Earth, and the state of the core.
Biography of T Guy Masters
Dr. Masters, Green Scholar, 1979
Dr. Masters obtained his PhD from Cambridge University
in 1979 under the joint supervision of Jack
Jacobs and David Gubbins.
His thesis focused on the use of inverse techniques
to determine the thermal and chemical state of the deep Earth using
free-oscillation frequencies as data. A secondary focus was the use of
thermodynamic techniques to evaluate the efficiency of various ways of
driving the geodynamo. These two threads are connected by the need to
use free-oscillation data to determine the density jump at the inner core
boundary which, in turn, determines the importance of chemical buoyancy for
driving the geodynamo.
This early exposure to free-oscillations led Dr. Masters to post-doc with
Freeman Gilbert at IGPP in San Diego (the theoretical font of free-oscillation
seismology and the driving force behind a then-new global network of long-period
seismometers). A recipient of a Green Scholarship, Dr. Masters
spent the first two years of his post-graduate career
developing the infrastructure to handle the large digital seismic data sets that
were just becoming available. This work resulted in several observational firsts:
- The first recognition of “anomalous” splitting of free oscillations
sensitive to the core (the cause of which was later ascribed to inner core
anisotropy by researchers at Harvard — perhaps still a little controversial)
- The first observation of large-scale structure in the upper mantle and
transition zone using normal mode peak shifts — this paper is considered
to be one of the first contributions to modern global seismic tomography.
- The first observation of strong coupling between normal modes (due to
coupling by the Coriolis force)
These breakthroughs helped Dr. Masters achieve the position of
Associate Professor in 1985 and full Professor in 1990.
The lack of major earthquakes in the 80s and a desire to get high
resolution images of Earth's 3D structure caused Dr. Masters to temporarily give
up free-oscillation research and begin a large program of measurement of
long-period body waves. An analysis of a global dataset of SS-S measurements
demonstrated the feasibility of using long-period travel times in
global seismic tomography and an analysis of long-period
ScS-S times gave one of the first direct observations of long-wavelength
shear-velocity structure at the base of the mantle. Stacking
techniques to look at precursors of SS also led to one of the first maps of
topography on the 660km discontinuity.
Early attempts to use the mode and body wave data to do mantle tomography made
it clear that better constraints on upper mantle structure were needed. This
led to a new direction of research using surface wave polarization with
then-graduate student Gabi Laske. This research demonstrated that polarization
of surface waves gives a new sensitive datum for looking at structure near the
surface. The various lines of research
(body-wave, free-oscillation, surface waves) were combined to make new 3D models
of mantle structure and have now been extended to make joint models of
P and S velocity which allow assessment of the physical cause of mantle
velocity anomalies. An interesting aspect of the joint models is the
anticorrelation between shear velocity and bulk sound speed in the lowermost
mantle which implies a non-thermal source for the anomalies in this region.
Dr. Masters with two “waterwitches”, 2002
Recently, Dr. Masters has returned to free-oscillation research (due to the
occurence of several major earthquakes from 1994 onwards). Rather than just
applying the old data analysis techniques to the new data, Dr. Masters has
developed new ways of analyzing mode data and has applied
a subset of this theory (with Laske) to evaluate claims of superrotation of the inner core.
The bottom line is that mode data do not support a significant
superrotation of the inner core though relative rotation rates of 0.2 degrees
per year can not be ruled out.
The main theme flowing through Dr. Masters research is the imaging and
interpretation of seismic structure on a global scale. To do this successfully
requires a large amount of data of various types (body wave, surface wave,
modes). Dr. Masters group at SIO is one of a hand–full worldwide which is
involved in this endeavor.
Dr. Masters was elected fellow of the AGU in 1995. He has served in various roles inside and outside
of UCSD including being vice-chair of the SIO
department and Director of the Earth Sciences program at UCSD (from 1999 to 2002).
Links
|
