Adam M. Dziewonski - US grants

The proposed continuation of global and regional studies of earthquake source mechanism using waveforem inversion will cover the following topics: 1. Continuation of the centroid-moment tensor (CMT) analysis of current events using GDSN, and other - as available - data, with the results sent to the USGS on a monthly basis and submitted quarterly for publication in the Physics of the Earth and Planetary Interiors. 2. Utilization of the data from the High-Gain Long-Period (HGLP) network operating between 1972 and 1976; this was the first global digital network and little use has been made of it; will determine station responses and sensitivities; permanent storage on the optical media (WORM type discs); 3. CMT and very broad bank (VBB) analysis of the HGLP data for selected events between 1972 and 1976; this period is characterized by many large earthquakes lacking, so far, proper analysis; 4. Systematic search for events with a statistically significant non-double couple component; it is highly likely that there are events which have an unusual source mechanism: two events near Torishima Island, south of Japan and three events on Iceland have mechanism that appear to be consistent with being caused by magma injection. ***

This award provides approximately one-half the funds needed to acquire an optical mass storage module to be installed in the Department of Earth and Planetary Sciences at Harvard University. The storage system has a capacity of 165 gigabytes and will be controlled by a computer which can be accessed by the Harvard university-wide Ethernet system and the national NSFnet system. Digital seismograms recorded by the global seismic network since 1972 already constitute approximately 100 gigabytes of scientific data with many potential applications such as studies of seismic sources and deep-earth tomographic imaging. The data set is very large and growing, and it currently resides on 5000 magnetic tapes. Direct, on line, access to this data transferred to the optical storage system is the only practical means of scientifically processing this resource.

The proposed continuation of studies of the three-dimensional structure of the mantle expoit the large data sets created under previous funding, and the inversion techniques which have been developed, to recover more complete information on mantle heterogeneity and to quantify the uncertainty of the resulting models. It is proposed to study the P-wave heterogeneity of the upper mantle, to assess the requirement for anisotropy and to implement a number of extensions and enhancements of present techniques aimed at increasing the information which can be extracted from the data.

The progress achieved during the last four or so years in seismic tomography of the mantle has created favorable conditions to attempt a major effort in delineating aspherical properties of the Earth from region D" to the inner core. We can now be confident that our current models are adequate to strip the long wavelength effect of lateral heterogeneity in the outermost 2700 km. We propose to use travel time (primarily ISC data base) and waveform data.

This research is to advance the knowledge of three dimensional structure of the Earth's mantle. The improvement of P- and S- wave velocity models will be accomplished through expansion of the following observations: augmentation of the waveform data bases using data from many new broad-band digital stations deployed after 1984, expansion of absolute and differential travel-time data sets measured from digital seismograms, and development of a new "summary travel time" data base from ISC Bulletins containing seismic station-source region anomalies. Acquisition of this data base will be followed by a joint inversion of waveforms and traveltimes; in the past these data were treated separately. In addition to this primary objective, the acquired data will allow the examination for large scale anisotropy and lateral variations in Q.

This award provides 50% of the funds required for the acquisition of a computer file server system required for the research of the seismology group in the Department of Earth and Planetary Sciences at Harvard University. The University is committed to providing the remaining funds needed for the acquisition. The computer system will allow the researchers to address a broad range of problems dealing with the interpretation of data from globally distributed digital seismographic stations to arrive at the Earth's three-dimensional internal structure from its crust to the core.

This research is to continue the valuable program to catalog centroid-moment tensor (CMT) solutions from global digital seismic data on a routine basis. The Harvard CMT catalog has become a significant resource for the seismological community in global tectonic studies. In addition, research will be done on large deep earthquakes lying away from the most intense seismic activity in Wadati-Benioff zones, and on better methods for parameterizing source time functions of earthquakes. These studies are fundamental to seismological research and the origin and distribution of earthquakes. This research is a component of the National Earthquake Hazard Reduction Program.

Until now, seismic Modelling of three dimensional Earth structure and the study of mantle convection have been performed separately, with the latter occasionally employing, a posteriori, the results of the former. One objective of this project is to further advance understanding of mantle dynamics by performing simultaneous inversions of long-period seismic waveform data and geodynamic data consisting of the observed plate velocities and nonhydrostatic geoid. The second objective is to further refine previous treatments of viscous flow in the mantle. The simultaneous consideration of seismic and geodynamic data will help to stabilize the seismic inverions in those geographical areas that are poorly resolved and it will also allow one to address important issues in solid-Earth physics and geodyamics.

This research is a 5-year continuation of investigations carried out under two former grants dealing with earthquake source analysis and earth structure. Topics include 1) continuation of the ongoing Centroid Moment Tensor (CMT) analysis; 2) refining the CMT analysis procedure through the combined use of waveforms and travel time observations; 3) extending the CMT procedure to the analysis of smaller events by the use of teleseismic surface waves; 4) using SKKS and SKS observations, in conjunction with 3D mantle models, to constrain outer core structure; 5) using combined data sets to obtain improved spherically symmetric reference Earth models; 6) performing joint inversions for the P and S 3D-velocity structure of the mantle; 7) performing modeling experiments based on joint inversion of seismic and geodynamic data, as well as exploring the geodynamic implications of the 3D velocity models; 8) including higher frequency data in the 3D earth structure modeling experiments in order to improve radial and lateral resolution; 9) developing procedures for hybrid region/global model parameterizations which will allow for proper inversions for large- scale regional structure; 10) investigation of mantle anisotropy and lateral variation in attenuation and how these phenomena may be accounted for in the 3D modeling experiments. The service provided by these efforts to the world seismological community, especially the CMT catalog, is widely used in determination of earth structure, tectonics, and earthquake analysis. This research is a component of the National Earthquake Hazard Reduction Program.

This award will provide partial funding for a systems manager to support the computer system of the geophysics research group in the Department of Geological & Planetary Sciences at Harvard University. The computer facility presently serves 15-20 faculty, postdoctoral research associates, graduate and undergraduate students working in computer-intensive areas of research such as seismic tomography, earthquake seismology, geomagnetics, and other studies of the Earth's deep interior.

9305890 Dziewonski This project initiates a community-wide study of the core-mantle boundary, one of the most significant regions of our planet. As a result of the past decade's research advances, the geosciences community is on the verge of making significant breakthroughs in understanding how the Earth evolves on a global scale. Because the dynamics of the deep planetary interior involves many different facets of the Earth sciences, from geomagnetism and seismology to mineral physics and geodynamics, a multi-disciplinary approach is essential. An average of less than $30 K/yr for each investigator will allow them to pursue this effort in a truly collaborative and interdisciplinary manner. This project will yield important new observations and theoretical analyses bearing on the core-mantle boundary, and will support the participation of the broader community of interested geoscientists. Significant advances in our understanding of the Earth's geological evolution -- far beyond what would be achieved by the individual groups working separately -- will result from this collaborative, multi-disciplinary effort. ***

0214069
Ekstrom

This grant provides support to upgrade the Harvard Seismology computing facility in order to facilitate a broad range of research in seismology and geophysics. The upgrade will include a fast multiprocessor server with large shared memory and a large-volume fast-access disk array. The activities supported by the new infrastructure include earthquake studies focused around the Harvard CMT project. An important component of this project is the systematic analysis of all earthquakes with magnitudes greater than approximately 5.2 around the world, using digital data from globally distributed seismographs. A second component of the supported activities involves imaging of the elastic properties of the Earth's interior. This research is pursued by development of new data sets and the joint inversion of various existing data sets, such as absolute and differential travel times, surface-wave dispersion curves, full waveforms, and normal-mode spectra. The upgraded computer facilities will allow a more detailed parameterization of Earth structure and a higher fidelity imaging of the Earth's interior.
***

9615677 Ekstrom This grant provides $149,829 as partial salary support for a technician responsible for network administration for the seismology computer facility at Harvard University. This is a Phase II technician support proposal under the EAR/IF technician support sub-program and as such, will continue support of this technician for an additional two-years beyond the first three years of technical support (EAR-9219192). The seismology group at Harvard conducts world-class research on global tomographic models, studies of Love and Rayleigh wave propagation in the crust and upper mantle and continues service to the seismological community via their efforts at calculating waveforms, travel times, complete seismograms etc. from data generated from the IRIS Global Seismographic Network (GSN). This grant will provide technical service to a large group (20 faculty, graduate and undergraduate students) of seismologists. Additionally, the University, under the guidelines for a Phase II technician support proposal under the EAR/IF program is committed to support of this position for a minimum of two-years beyond expiration of this Phase II award, ***

Dziewonski
EAR-0207608

The principal objectives of this project are the systematic investigation of global seismicity and the three-dimensional mapping of the Earth's interior. The earthquake studies are focused around the Harvard CMT project. All earthquakes with magnitudes greater than approximately 5.2 are analyzed for their source mechanisms using digital data from globally distributed seismographs. Unusual seismic phenomena, such as slow earthquakes, volcanic collapses, and unidentified seismic signals, are investigated in detail. Results are disseminated using electronic mail and the Harvard Seismology web page: http://www.seismology.harvard.edu. The imaging of the elastic properties of the Earth's interior is pursued by development of new data sets and the joint inversion of various existing data sets, such as absolute and differential travel times, surface-wave dispersion curves, full waveforms, and normal-mode spectra. Particular consideration is given to the inclusion of anisotropy (radial, azimuthal, and general) in the model parameterization and inversion. Models and derived data sets are available on the investigators' web site.
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This project consists of two linked investigations into the large-scale elastic and anelastic structure of the Earth's mantle. The first study concerns the development of a three-dimensional model of shear attenuation in the Earth's upper mantle. The model is constrained by a large data set of Love and Rayleigh surface-wave amplitude measurements in the period range 50--250 seconds. A new method, which removes extraneous effects on wave amplitude by solving for them as part of the inversion, is used. Preliminary results of this approach applied to the mapping of Rayleigh wave attenuation show that it successfully isolates the signal due to attenuation in the amplitude data. Three-dimensional finite-frequency kernels will be incorporated in the inversion to account for the spatially broad sensitivity of the long-period surface waves considered here. A simultaneous inversion for the anelastic and elastic structure of the upper mantle will both account for and be constrained by the effects on wave amplitude of focusing by velocity heterogeneity. The 3-D attenuation model developed in this study will be used to address still-unresolved but fundamental questions regarding the underlying causes of large-scale elastic and anelastic heterogeneity in the upper mantle, including temperature, composition, water, and partial melt.

The second study is aimed at advancing the mapping of the large-scale anisotropic structure of the Earth's mantle, and developing a regional-scale model of the elastic structure beneath Eurasia. This work expands existing collections of dispersion measurements, cross-correlation travel times, and long-period waveforms, and inversion of the data simultaneously for three-dimensional Earth structure. Work to date has included inversion for a new one-dimensional anisotropic mantle for the upper mantle without a discontinuity at 220 km depth and the development of a new technique to account for the non-linear effects of crustal structure on long-period waveforms. Tomographic models of radially anisotropic three-dimensional structure for the whole mantle are developed, and a careful resolution analysis will be conducted to determine where anisotropy is required by the observations. Building on the global model, a multi-resolution parameterization will be employed to develop a model with greater lateral resolution beneath Eurasia.The tomographic models (elastic and anelastic) developed in this project will be useful for direct interpretation in terms of composition and state of the Earth's mantle. The research will lead to the development and distribution of several data products, including collections of direct measurements and tomographic models, as well as computer programs to make use of these products.

This award is funded under the American Recovery and Reinvestiment Act of 2009
(Public Law 111-5)


Abstract

During the last quarter of a century many 3-D models of the mantle, or its part, have been derived. However, most of them describe only one parameter (for example, S-velocity) and are based on a data set that is limited to a narrow range of frequencies. This has limited the range of conclusions that could have been drawn from these models. Here we request two-year support for investigation of elastic and density structure of the Earth's interior using a wide variety of seismic data, with resolution spanning depth range from the surface to the Earth's center and frequencies from 1Hz to 0.3 MHz. In particular, we propose to:
start with Kustowski et al. (2008) data sets, programs, and models
assemble an additional data set of normal mode center frequencies
assemble an additional data set of normal mode splitting functions
assemble an additional data set of ISC travel times and other sets of travel time data, including a large set of waveform derives travel times measured at Scripps Institution of Oceanography.
integrate the three new data sets with those used by Kustowski et al.(2008) to invert for a 3-D mantle model that includes radically anisotropic elastic bulk sound and shear velocities and the topographies of the 410 km, 650km and core-mantle boundary.

The new database, covering a wide range of frequencies, will allow us to perform joint inversion for elastic parameters and density, and investigate the importance of large-scale isotropic and anisotropic variations within the mantle. The simultaneous inversion will assure self-consistency. It will put stronger constraint on density structure compared to mode-only inversion by limiting leakage of power from elastic variations to density. The robustness of the density heterogeneity will be established with this data set, and will contribute to resolution of the controversy surrounding the elusive, and yet important, density model. These new elastic and density models will play a major role in addressing such questions as the dynamics of the mantle, its thermal and chemical state, and distribution of partial melt.

Intellectual Merit. The proposed research will lead to a suite of models describing the variations in elastic parameters (isotropic and anisotropic seismic wave speed perturbations) and density within Earth's mantle. It will address the controversy surrounding three-dimensional density model. The new models will provide basis for testing relative importance of thermal and chemical variations as well as partial melting and different scenarios for mantle convection.

Broader Impacts. The new model will provide important information for geodynamicists, geo-chemists, mineral physicists and, of course, seismologists. Combination of the new models Provides essential constraint on the understanding of the state of the mantle (i.e., heterogeneity in thermal and compositional anomalies, and partial melt). They are also closely related to dynamics, and can be used in studies such as those on mantle convection and large-scale gravity modeling. This project will also be a part of a museum display on solid Earth that is being planned for 2007-2009 at the Harvard Museum of Natural History.

Elastic properties of the Earth's interior (e.g. density, rigidity, compressibility, etc.) vary with location due to changes in temperature, pressure, composition, and flow. In the 20th century, Earth scientists have used seismic waves emitted by earthquakes and explosions to develop models of how Earth properties vary with depth. Community reference models that grew out of these efforts have proven indispensable in earthquake location, imaging of interior structure, understanding material properties under extreme conditions, and as a reference in other fields, such as particle physics and astronomy. Over the past three decades, more sophisticated efforts by seismologists across the globe have yielded several generations of models of how properties vary not only with depth, but also laterally. Yet, though these three-dimensional (3D) models exhibit compelling similarities at large scales, differences in the methodology, representation of structure, and dataset upon which they are based, have prevented the creation of 3D community reference models. The investigators propose to overcome these challenges by compiling, reconciling, and distributing a long period reference seismic dataset, from which they will construct a 3D seismic reference model (REM-3D) for the Earth's mantle. As a community reference model and with fully quantified uncertainties and tradeoffs, REM-3D will facilitate Earth imaging studies, earthquake characterization, inferences on temperature and composition in the deep interior, and be of improved utility to emerging scientific endeavors, such as neutrino geoscience. The investigators will set up community working groups that will serve to advise during the process of reference model and dataset development, and will organize a workshop to assess progress, evaluate model and dataset performance, identify avenues for improvement, and recommend strategies for maximizing model adoption in and utility for the deep Earth community. To this end, the investigators have solicited input from seismologists, mineral physicists, geodynamics, and geochemists from around the United States and internationally.

The investigators propose to develop a three-dimensional seismic reference model (REM-3D) for the Earth's mantle, parameterized in terms of shear wavespeed (Vs), compressional wavespeed (Vp), density (ρ), and the 3 additional parameters representing radial anisotropy. Two versions of the model will be developed to explicitly fit the comprehensive, community-contributed long period seismic dataset, one parameterized in terms of spherical harmonics, and the other as canonical profiles corresponding to major geographic provinces. Furthermore, they will compile, reconcile, and distribute a long period reference seismic dataset, including surface wave dispersion measurements, long period absolute and differential body wave measurements, and free oscillation frequencies / attenuation / and splitting. Unlike previous reference models of Earth structure, REM-3D will have fully quantified. The investigators will also create online tools for model distribution and for predicting various seismic observables, including full waveforms, as well as tools designed primarily to enable mineral physicists and geodynamicists a straightforward way of (in)validating test models against this reference model or directly against the reference dataset. Finally, the investigators will set up community working groups and organize workshops that will advise on and evaluate model and dataset performance, identify avenues for improvement, and recommend strategies for maximizing model adoption in and utility for the deep Earth community. REM-3D will benefit the broader scientific community by facilitating: 1. Mineralogical and thermo-chemical interpretation of seismic velocities and density; 2. Identification of anomalous / atypical structures in the Earth's mantle; 3. Comparison of global and regional tomographic models; 4. Seismic waveform interpretation, such as the identification of particular seismic phases; 5. Inversion for 3D Earth structure requires a starting or background model; 6. Earthquake source characterization using long period data. The construction of a community-contributed reference dataset will make possible the identification of anomalous seismic wave travel times, surface wave dispersion, normal mode splitting, and waveform features. Furthermore, the tools for predicting seismic observables from input structures that we will create will enable direct evaluation of potential velocity structures predicted by mineral physics and geodynamics experiments and calculations.