Research

Research Highlights

• Inner core anisotropy can be explained by an inner core comprising hexagonally closed-packed iron-nickel alloy growing faster in the east and slower in the west published in Nature Geoscience (2021)

• Upper mantle velocity structure can contaminate differential travel-time measurements and bias estimates of inner core anisotropy causing the “Alaska anomaly” published in PEPI (2021)

• Array measurements of inner core waves in Alaska show perturbations in direction and travel time by the subducted Pacific plate. published in PEPI (2020)

• Inner core anisotropy shows a gradual depth dependence without the need of a distinct innnermost inner core published in PEPI (2019)

• Array measurements of novel seismic waves support models of weak inner core anisotropy at shallow depths. published in GRL (2017)

• SEMUCB_WMQ : 3D global upper mantle shear velocity, radial anisotropy and attenuation model developed using full waveforms published in Geophysical Journal International (2018)

• Seismic evidence for partial melting at the root of major hot spot plumes, published in Science (2017)

• SEMUCB_WM1: Broad plumes rooted at the base of the mantle beneath major hotspots, published in Nature (2015), and the corresponding SEMUCB_WM1 (or SEMUCB-WM1) whole mantle radially anisotropic shear velocity model developed using full waveform inversion.

• SEMum2: Low velocity channels in the oceanic asthenosphere from full waveform inversion using the Spectral Element Method, published in Science (2013), and the corresponding SEMum2 upper mantle, radially anisotropic shear velocity model developed using full waveform inversion.

• An unsually large ULVZ at the base of the mantle near Hawaii, published in EPSL (2012)

• SEMum: First global upper mantle shear velocity model developed using the Spectral Element Method, published in GJI (2011)

• Lithospheric layering in the North American craton, published in Nature (2010)

• Depth distribution of anisotropy in the continental upper mantle, published in Nature (2007) earlier site

• Short wavelength topography on the inner core boundary, published in PNAS (2007)

• Detection and identification of PKJKP, published in Science (2005)

• Origin of the earth's "hum", published in Nature (2004)

• Radial anisotropy at the base of the mantle, published in Science (2004)

• Anisotropy and thickness of the lithosphere, published in Nature (2003)

• Superplumes from the core mantle boundary to the lithosphere, published in Science (2002)

BSL Annual Report Pages

Report pages of group members submitted to the [BSL Annual report].

Theoretical Wave Propagation

Whether through the use of finite frequency kernels or fully numerical approaches, the Global Seismology Group continues its commitment to applying the latest theoretical and computational advances to the study of Earth structure. more details

Global Elastic Waveform Vectorial Tomography

The Global Seismology Group has pioneered the use of full-waveform tomography using finite frequency kernels (see Theory above), and we have produced a number of models of the velocity and anisotropic structure of the mantle. more details earlier writeup

Global Anelastic Waveform Tomography

We have have been a trailblazer in using tomographic techniques to map the distribution of seismic attenuation in the Earth's mantle. more details

Regional Vectorial Tomography

Taking advantage of the unprecedented coverage of North America made available by recent PASSCAL and USARRAY deployments, we have undertaken a series of studies looking at the velocity and anisotropic structure beneath North America. Model 2010 more details Model 2014 more details

Study of D" Region

The mantle's lower thermal boundary layer, also known as D", has been the subject of waveform modeling and tomographic study by the Global Seismology Group. Our investigations have revealed strong seismic heterogeneity in D", and have provided insight into flow occurring within and the thermochemical state of this fascinating region of the Earth. more details

Study of the Core

Using observations of free oscillations and higher frequency body waves, the Global Seismology Group has probed Earth's very center. Our study of this remotest part of our planet has helped constrain its dynamics and thermochemical state. more details earlier writeup

The Earth's Hum

The Global Seismology Group has been actively researching the processes by which seismic waves are excited, be they earthquakes themselves or ocean-atmosphere-lithosphere interactions giving rise to Earth's evepresent "hum". more details earlier writeup

Instrumenting the Ocean Floor

In an effort to gain experience in deploying and maintaining ocean-bottom seismometers, a three component very broadband seismometer package (CMG-1T), recording system, as well as auxiliary differential pressure gauge (DPG) and current meter, were installed on the seafloor, in Monterey Bay, 40 km off-shore, at 1000m water depth. more details