My name is Raúl Valenzuela Wong. I am an Assistant Professor
in the Department of Seismology and Volcanology at the Institute of
Geophysics of the Mexican National University since March 1997. I
graduated from Washington University's Department of Earth and Planetary Sciences.
Understanding the state and dynamics of the Earth's deep interior has been an area of very active, multidisciplinary research for the past fifteen years. The interactions between the core and the mantle, with their differences in chemical composition at high temperatures and pressures, influence processes such as mantle convection, the formation of mantle plumes, plate tectonics, variations in the magnetic field, and perhaps life itself!
My current research focuses on determining the lateral and radial
shear velocity structure of D", the lowermost layer of the
mantle, using horizontally polarized diffracted shear waves.
Local changes in the composition and temperature of the base of
the mantle affect the seismic velocity.
Lateral heterogeneity at the core-mantle boundary.- I
use diffracted shear waves (Sdiff) recorded by stations
at epicentral distances greater than 95° and arranged in
a profile with a narrow azimuthal distribution. Travel time
corrections are applied to account for Earth's ellipticity and
mantle heterogeneity. Apparent ray parameters are determined
by least-squares fits through the pulse maxima of the ground displacement
records. The lateral heterogeneity of the CMB is quantified by
comparison with the slowness obtained from reflectivity synthetic
seismograms for the standard model PREM. For this study I use
global digital data from the NEIC CD-ROMs for the period from
January 1980 to June 1987. D" heterogeneities of ±3.75%,
relative to PREM, have been observed. [Valenzuela, 1996;
Wysession et al., 1995; Valenzuela et al., 1993].
Velocity models of the lower mantle from IRIS PASSCAL data.-
I have determined the velocity structure of
the base of the mantle under eastern Siberia using data from the
Tibetan Plateau Passive Seismic Experiment deployed by Tom Owens
and collaborators from July 1991 to June 1992. I have determined
the frequency dependent decay constant of horizontally polarized
S and Sdiff waves from the records of five earthquakes
in northern California. I compare the observed decay constant
with that obtained from reflectivity synthetic seismograms generated
from forward models of the base of the mantle. My preferred model
for the velocity structure under eastern Siberia shows a discontinuous
velocity increase at the top of D", followed by a gradual
decrease down to the core-mantle boundary. [Valenzuela,
1996; Valenzuela et al., 1994].
Participation in the Missouri to Massachusetts deployment.-
I also have field experience installing and operating seismic
equipment. I participated in the deployment of the Missouri to
Massachusetts array (MOMA). I determined the decay constant using
an earthquake in the Kermadec Islands. The velocity structure
of D" under the east central Pacific Ocean shows a discontinuity
similar to the one observed under eastern Siberia. [Valenzuela,
1996; Valenzuela et al., 1996a; Wysession et al.,
Earthquake relocation and seismotectonics. Intraplate seismicity
of the southern Tasman Sea.- I relocated the intraplate earthquakes
originally reported in the southern Tasman Sea in order to compile
a reliable catalog. The relatively high level of intraplate seismicity
in the southern Tasman Sea suggests that this region may be undergoing
internal deformation as a consequence of the tectonic stresses
generated at the Australia-Pacific plate boundary, where initiation
of subduction might be taking place. I also discovered evidence
of seismicity on a fracture zone dating as far back as 1924.
[Valenzuela and Wysession, 1993].
Waveform modeling to constrain depth and source parameters.
Macquarie Ridge Complex.- I have used synthetic seismograms,
generated by ray summation, to constrain the depth and source
parameters of the seismic source. In particular, this work focused
on the Macquarie Ridge Complex (MRC). The MRC represents a segment
of the Australia-Pacific plate boundary and it is a site where
the initiation of subduction might be taking place. In 1989,
the largest earthquake in a decade occurred at the MRC. Other
earthquakes show both strike-slip and thrust focal mechanisms
and most of them are shallow.
Fluorescence of americium in a fluorozirconate glass.-
During my time as a Physics undergrad I did research on the fluorescence
of the actinide element americium. The americium was chemically
combined with a glass. After cooling the sample to temperatures
around 10 K and using a dye laser to excite the americium electrons
to higher energy levels, it is possible to observe the light emitted
(fluorescence) as the electrons relax back to lower levels. In
this study I determined the states and energy levels involved
in such electronic transitions. [Valenzuela and Brundage,
Here's the link to my list of Publications and Presentations.
Thank you for dropping by.
You can contact me at:
Depto. de Sismología.
Instituto de Geofísica - UNAM.
Circ. Investigación S/N.
04510. México, D. F.