Miaki Ishii
Assistant Professor of Earth and Planetary Sciences

	Department of Earth and Planetary Sciences Harvard University Room 202B, Museum Building 20 Oxford Street Cambridge, MA 02138 Telephone: (617)384-8066 Fax: (617)495-0635 E-mail

Research Interests

My main interest is to use recordings of seismic energy to image the internal structure of the Earth and to study properties of earthquakes. Just as X-ray (CAT scan) and MRI provide non-invasive ways of viewing the inside of human body, different geophysical data can be deciphered to obtain pictures of the Earth's interior without sending instruments deep down. Seismological observations are particularly suitable for such study, and allow us to see the internal structure from different angles. These data also contain clues about source of the energy, i.e., how the Earth slipped to cause earthquakes.

A selection of my research results is listed below.

December 26, 2004 Sumatra-Andaman Earthquake An animation showing the rupture propagation/high-frequency energy radiation during the December 26, 2004 Sumatra-Andaman earthquake which devastated countries around the Indian Ocean. Red star denotes the epicentral location. Time from the beginning of the event is given at the top-left corner. "New Method for Imaging Dec. 26 Indian Ocean Earthquake Yields Unprecedented Results" (Scripps Institution of Oceanography News)

Anisotropy of the Earth's Inner and Innermost Inner Core An illustration of the Earth's interior, showing heterogeneous mantle (layer with colours varying from red to blue), homogenous outer core (pale blue layer), and anisotropic inner (pink) and innermost (red) inner core. Using seismic waves recorded at antipodal distances (~180 degrees from the source, i.e., on the other side of the globe), the peculiarity of the central 300 km of the inner core (innermost inner core, red region) is inferred. "Earth's New Center" (Harvard Gazette)

3-D Mantle Models Using Normal-Mode Data 3-D models of large-scale variations within the mantle can be obtained from normal modes or free oscillations of the Earth. These models show that the regions of high (blue) and low (red) shear-wave speed (top) are anti-correlated with those of bulk-sound speed (middle) near the core-mantle boundary. Furthermore, at this depth (2850 km), lateral variations in density (bottom) is regionally anti-correlated with shear-wave speed variations (e.g., underneath the Pacific and Africa). This observation suggests that considerable amount of compositional heterogeneity exists in the lowermost mantle.

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