Miaki Ishii

Last updated
Miaki Ishii
Alma mater
Awards James B. Macelwane Medal
Scientific career
Fields Seismology
Institutions
Thesis Large-Scale Structure of the Earth's Mantle and Inner Core  (2003)
Doctoral advisor Jeroen Tromp
Website Research site

Miaki Ishii is a seismologist and Professor of Earth and Planetary Sciences at Harvard University.

Contents

Education and early career

Ishii attended secondary school at Midland Secondary School in Ontario, Canada, graduating in 1994. [1] She then studied physics at the University of Toronto, where she received her Bachelor of Science degree with honors in 1998. During her undergraduate career, she conducted research on glacial rebound under the mentorship of Jerry X. Mitrovica. [1]

Ishii attended Harvard University for her doctoral work under the mentorship of her supervisor Jeroen Tromp. There, she worked to measure variations in the lateral density of the Earth's mantle using seismic data. [2] She found that there is heterogeneity in the composition of the lowermost mantle, with denser than average material beneath the Pacific Ocean and Africa. [3] Together with seismologist Adam Dziewonski, Ishii also identified a region of the Earth's core, which they called the innermost inner core, which is located in the central part of the inner core and exhibits a distinct anisotropy—or pattern of wave propagation—relative to the bulk of the inner core. [4] [5] She published her doctoral work studying the Earth's mantle and inner core in a thesis entitled Large-Scale Structure of the Earth's Mantle and Inner Core and received her Ph.D. in 2003. [6]

Between 2003 and 2005, Ishii worked as a postdoctoral researcher at Scripps Institution of Oceanography at the University of San Diego, working to collect High-Sensitivity Seismograph Network (Hi-net) data from Japan. She was able to back-project the data to map the 1200-km-long rupture that was associated with the 2004 Boxing Day earthquake and tsunami that devastated Sumatra. [7] [8] She and her colleagues, who included seismologist John Vidale, found that the event lasted 480 seconds and was characterized by a steady rupture velocity of 2.5 kilometers per second. The method they employed is now known as "beam-back projection" in which a series of seismometers are retroactively trained on the site of a single large seismic event and used to track where the seismic energy was released in time. [9]

Research

In 2006, Ishii became an Assistant Professor of Earth and Planetary Sciences at Harvard University. She was promoted to Associate Professor in 2010 and became a full Professor in 2013. There, she uses recordings of seismic energy to understand the composition and structure of the Earth's interior and to study the properties of earthquakes. One of the objectives of her research is to build faster methods to more accurately locate and characterize earthquakes that have occurred around the world in order to better understand what kinds of earthquakes to expect in the future. [10]

Through her research program, Ishii has continued to refine and enhance the back projection methods she developed as a postdoctoral fellow. She integrates data taken by networks of seismic instruments from around the world, allowing her to more accurately map out the trajectory of earthquake waves. [10] Ishii has also made use of global positioning system (GPS) network data in order to search for deformities within Earth's internal structure. [10] The rocks and minerals that lie in the mantle—the layer of the Earth between the crust and the inner core—move in slow convection cycles due to the enormous heat and pressure that exist within the mantle. Ishii and her team are trying to understand the dynamics of those convection cycles over long periods of time, which can help scientists better understand the mantle's composition and potentially lead to more effective earthquake detection and warning systems.

When the Tōhoku earthquake and tsunami hit the Sendai region of Japan on March 11 2011, becoming the fourth biggest earthquake since 1900, Ishii applied her analysis methods to understand how the earthquake started and spread. [11] Previously, scientists had not believed this region was capable of experiencing an earthquake of this magnitude. Through preliminary computer simulations, Ishii and colleagues found that a long segment (about 390 km) of the Japan Trench had ruptured during the earthquake over the course of two to three minutes. [11] Ishii's analysis and visualization methodologies were also applied by The Washington Post reporters to characterize the Anchorage earthquake, a magnitude 7.0 earthquake which occurred in November 2018. [12]

Ishii has also studied the effects of underground testing of nuclear weapons, which were carried out in the mid- to late-20th century. [5] Unlike earthquakes, the precise epicenter of nuclear explosions is known; the waveform of an explosion is a simple spike. She leverages seismic data collected by a series of instruments belonging to the Preparatory Commission for the Comprehensive-Test-Ban Treaty Organization (CTBTO), a Vienna-based organization that monitors nuclear tests. [13] In addition to seismic data, the instruments also collect infrasound, hydroacoustic, and radiation data.

Ishii uses the seismic data to take, what she calls, an "X-ray" of the planet, studying how seismic waves bounce when they hit different layers of the Earth's interior. [14] Much like the X-rays and CAT-scans used in medical imagining, seismic waves bounce around and change direction based on the medium they pass through, which can give researchers an idea of the composition of Earth's interior. Ishii also uses these data to understand what happens at the boundary between the Earth's solid inner core and liquid outer core to understand how quickly the solid inner core is growing. [13]

Awards and honors

Selected publications

Related Research Articles

<span class="mw-page-title-main">Seismology</span> Scientific study of earthquakes and propagation of elastic waves through a planet

Seismology is the scientific study of earthquakes and the generation and propagation of elastic waves through the Earth or other planetary bodies. It also includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, glacial, fluvial, oceanic microseism, atmospheric, and artificial processes such as explosions and human activities. A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of Earth motion as a function of time, created by a seismograph is called a seismogram. A seismologist is a scientist works in basic or applied seismology.

<span class="mw-page-title-main">Geophysics</span> Physics of the Earth and its vicinity

Geophysics is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists, who usually study geophysics, physics, or one of the Earth sciences at the graduate level, complete investigations across a wide range of scientific disciplines. The term geophysics classically refers to solid earth applications: Earth's shape; its gravitational, magnetic fields, and electromagnetic fields ; its internal structure and composition; its dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation. However, modern geophysics organizations and pure scientists use a broader definition that includes the water cycle including snow and ice; fluid dynamics of the oceans and the atmosphere; electricity and magnetism in the ionosphere and magnetosphere and solar-terrestrial physics; and analogous problems associated with the Moon and other planets.

<span class="mw-page-title-main">Inge Lehmann</span> Danish seismologist (1888–1993)

Inge Lehmann was a Danish seismologist and geophysicist who is known for her discovery in 1936 of the solid inner core that exists within the molten outer core of the Earth. The seismic discontinuity in the speed of seismic waves at depths between 190 and 250 km is named the Lehmann discontinuity after her. Lehmann is considered to be a pioneer among women and scientists in seismology research.

<span class="mw-page-title-main">Mohorovičić discontinuity</span> Boundary between the Earths crust and the mantle

The Mohorovičić discontinuity – usually called the Moho discontinuity, Moho boundary, or just Moho – is the boundary between the crust and the mantle of Earth. It is defined by the distinct change in velocity of seismic waves as they pass through changing densities of rock.

Seismic tomography or seismotomography is a technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions. P-, S-, and surface waves can be used for tomographic models of different resolutions based on seismic wavelength, wave source distance, and the seismograph array coverage. The data received at seismometers are used to solve an inverse problem, wherein the locations of reflection and refraction of the wave paths are determined. This solution can be used to create 3D images of velocity anomalies which may be interpreted as structural, thermal, or compositional variations. Geoscientists use these images to better understand core, mantle, and plate tectonic processes.

<span class="mw-page-title-main">Beno Gutenberg</span> German-American seismologist

Beno Gutenberg was a German-American seismologist who made several important contributions to the science. He was a colleague and mentor of Charles Francis Richter at the California Institute of Technology and Richter's collaborator in developing the Richter magnitude scale for measuring an earthquake's magnitude.

<span class="mw-page-title-main">Core–mantle boundary</span> Discontinuity where the bottom of the planets mantle meets the outer layer of the core

The core–mantle boundary (CMB) of Earth lies between the planet's silicate mantle and its liquid iron–nickel outer core, at a depth of 2,891 km (1,796 mi) below Earth's surface. The boundary is observed via the discontinuity in seismic wave velocities at that depth due to the differences between the acoustic impedances of the solid mantle and the molten outer core. P-wave velocities are much slower in the outer core than in the deep mantle while S-waves do not exist at all in the liquid portion of the core. Recent evidence suggests a distinct boundary layer directly above the CMB possibly made of a novel phase of the basic perovskite mineralogy of the deep mantle named post-perovskite. Seismic tomography studies have shown significant irregularities within the boundary zone and appear to be dominated by the African and Pacific Large Low-Shear-Velocity Provinces (LLSVP).

<span class="mw-page-title-main">Earth's inner core</span> Innermost part of Earth, a solid ball of iron-nickel alloy

The earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about 1,220 km (760 mi), which is about 20% of Earth radius or 70% of the Moon's radius.

John Emilio Vidale is an American-born seismologist who specializes in examining seismograms to explore features within the Earth. He received the American Geophysical Union's James B. Macelwane Medal in 1994.

<span class="mw-page-title-main">Adam Dziewonski</span> American seismologist (1936–2016)

Adam Marian Dziewoński was a Polish-American geophysicist who made seminal contributions to the determination of the large-scale structure of the Earth's interior and the nature of earthquakes using seismological methods. He spent most of his career at Harvard University, where he was the Frank B. Baird, Jr. Professor of Science.

Episodic tremor and slip (ETS) is a seismological phenomenon observed in some subduction zones that is characterized by non-earthquake seismic rumbling, or tremor, and slow slip along the plate interface. Slow slip events are distinguished from earthquakes by their propagation speed and focus. In slow slip events, there is an apparent reversal of crustal motion, although the fault motion remains consistent with the direction of subduction. ETS events themselves are imperceptible to human beings and do not cause damage.

<span class="mw-page-title-main">Lunar seismology</span> Study of ground motions of the Moon

Lunar seismology is the study of ground motions of the Moon and the events, typically impacts or moonquakes, that excite them.

<span class="mw-page-title-main">Tsunami earthquake</span> Type of earthquake which triggers a tsunami of far-larger magnitude

In seismology, a tsunami earthquake is an earthquake which triggers a tsunami of significantly greater magnitude, as measured by shorter-period seismic waves. The term was introduced by Japanese seismologist Hiroo Kanamori in 1972. Such events are a result of relatively slow rupture velocities. They are particularly dangerous as a large tsunami may arrive at a coastline with little or no warning.

The 1970 Colombia earthquake occurred in Colombia on July 31.

<span class="mw-page-title-main">Inner core super-rotation</span> Concept in geodynamics

Inner core super-rotation is the eastward rotation of the inner core of Earth relative to its mantle, for a net rotation rate that is usually faster than Earth as a whole. A 1995 model of Earth's dynamo predicted super-rotations of up to 3 degrees per year; the following year, this prediction was supported by observed discrepancies in the time that p-waves take to travel through the inner and outer core.

<span class="mw-page-title-main">Innermost inner core</span> Solid core within the Earths liquid core

Earth is proposed to have an innermost inner core, distinct from its inner core. It is surrounded by the inner core, and is composed of solid iron in a different, but unknown structure from the inner core.

Maureen D. Long is an observational seismologist studying mantle and Mesosphere dynamics. She currently serves as a professor at Yale University within the Department of Geology and Geophysics.

Michel Campillo is a French seismologist and geophysicist who is currently a professor at Grenoble Alpes University.

Annie Souriau is a French seismologist from the commune of Saint-Cloud Paris. She is primarily known for her research into Earth's inner and outer cores, specifically her work examining seismic activity within and around the Pyrenees mountains. Through her and her colleague's research and studies, she has made notable advances to how humans understand the inner workings of the Earth's core while also winning many awards in the process.

<span class="mw-page-title-main">Seismic velocity structure</span> Seismic wave velocity variation

Seismic velocity structure is the distribution and variation of seismic wave speeds within Earth's and other planetary bodies' subsurface. It is reflective of subsurface properties such as material composition, density, porosity, and temperature. Geophysicists rely on the analysis and interpretation of the velocity structure to develop refined models of the subsurface geology, which are essential in resource exploration, earthquake seismology, and advancing our understanding of Earth's geological development.

References

  1. 1 2 "Miaki Ishii". physics.utoronto.ca. Retrieved 2019-10-18.
  2. 1 2 "Miaki Ishii". Honors Program. Retrieved 2019-10-18.
  3. ↑ Ishii, Miaki; Tromp, Jeroen (1999-08-20). "Normal-Mode and Free-Air Gravity Constraints on Lateral Variations in Velocity and Density of Earth's Mantle" (PDF). Science. 285 (5431): 1231–1236. doi:10.1126/science.285.5431.1231. ISSN   0036-8075. PMID   10455043. S2CID   13392802. Archived from the original (PDF) on 2020-04-03.
  4. ↑ Romanowicz, Barbara (September 14, 2016). "Adam M. Dziewonski (1936–2016)". Eos. Retrieved 2019-10-18.
  5. 1 2 Angier, Natalie (2012-05-28). "Earth's Core: The Enigma 1,800 Miles Below Us". The New York Times. ISSN   0362-4331 . Retrieved 2019-10-18.
  6. ↑ Ishii, Mikai (April 2003). Large-Scale Structure of the Earth's Mantle and Inner Core (PDF) (PhD thesis). Harvard University. Bibcode:2003PhDT.........5I. ISBN   9780496392940.
  7. ↑ Ishii, Miaki; Shearer, Peter M.; Houston, Heidi; Vidale, John E. (June 2005). "Extent, duration and speed of the 2004 Sumatra–Andaman earthquake imaged by the Hi-Net array". Nature. 435 (7044): 933–936. Bibcode:2005Natur.435..933I. doi:10.1038/nature03675. ISSN   1476-4687. PMID   15908984. S2CID   4415141.
  8. ↑ "New Method For Imaging Dec. 26 Indian Ocean Earthquake Yields Unprecedented Results". ScienceDaily. Scripps Institution of Oceanography. 26 May 2005. Retrieved 2019-10-18.
  9. ↑ Administrator, System (2005-05-26). "Imaging the earthquake". The Engineer. Retrieved 2019-10-18.
  10. 1 2 3 Powell, Alvin (2009-02-05). "Riding — and reading — the Earth tide". Harvard Gazette. Retrieved 2019-10-20.
  11. 1 2 Powell, Devin (2011-03-16). "Japan quake location a surprise". Science News. Retrieved 2019-10-20.
  12. ↑ Cappucci, Matthew (November 30, 2018). "Here's how the Anchorage earthquake happened". The Washington Post. Retrieved October 20, 2019.
  13. 1 2 Zhang, Sarah (2016-01-08). "The Hunt for Secret Nuclear Tests Digs Up Scientific Gold". Wired. ISSN   1059-1028 . Retrieved 2019-10-18.
  14. ↑ Kramer, Miriam (2012-06-15). "How Do We Know What's in the Earth's Core?". Popular Mechanics. Retrieved 2019-10-20.
  15. ↑ "Miaki Ishii". seismosoc.org. Retrieved 2019-10-20.
  16. ↑ "Miaki Ishii". nasonline.org. Retrieved 2019-10-18.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.