Karen M. Fischer

Last updated
Karen M. Fischer
BornJune 16, 1961 [1]
Boston, MA
Alma mater Massachusetts Institute of Technology, Yale University
Scientific career
InstitutionsBrown University
Thesis The morphology and dynamics of subducting lithosphere  (1989)
Doctoral advisor Thomas H. Jordan

Karen Fischer is an American seismologist known for her research on the structure of Earth's mantle, its lithosphere, and how subduction zones change over geologic history.

Contents

Education and career

Fischer has a B.S. in geology and geophysics from Yale University (1983). [2] While an undergraduate, Fischer had summer research experiences at Yale University and Lamont–Doherty Geological Observatory. [1] In 1989, she earned a Ph.D. in geophysics from the Massachusetts Institute of Technology (1989) with a dissertation titled "The morphology and dynamics of subducting lithosphere". [1] After a postdoctoral appointment at Lamont–Doherty Earth Observatory of Columbia University (1989-1990), [3] she joined the faculty at Brown University where she is the Louis and Elizabeth Scherck Distinguished Professor of Geological Sciences. [2]

From 2003 to 2005 Fisher was an editor at Geochemistry, Geophysics, Geosystems (G3) [4] and she served as the president of the Seismology section at the American Geophysical Union from 2013 to 2014. [5]

Research

Fischer's research uses seismology to study the interior of Earth's crust and mantle, especially in the lithosphere and the asthenosphere. [6] In the Marquesas Islands in the Pacific Ocean, Fischer identified unusually high temperatures in the lithosphere. [7] In the Tonga subduction zone, she used seismic data to map changes in the thickness of the subducting lithosphere [8] and modeled flow rates within the mantle. [9] [10] She has identified the presence of a continuous mantle on the East Pacific Rise [11] and discontinuities in the mantle under the eastern United States. [12] In the Appalachian Mountains, Fischer deploys broadband seismometers in the field [13] and uses the resulting data to define the thickness of the crust beneath the Appalachian Mountains. [14] [15] [16] Her research provides insight into age-related changes in the materials beneath old mountains [17] and discontinuities in the crust and mantle beneath the Appalachian Mountains [18] [19] and deformation in the plates beneath Southern California. [20] Her research on the lithosphere in South American and Africa [21] has implications for the stability of the tectonic plates in the region. [22] [23]

In 2019 she was received the Harry Fielding Reid Medal from the Seismological Society of America for "pioneering research on Earth’s upper mantle structure and dynamics, the structure and evolution of continental lithosphere, and the dynamics of subduction systems". [24]

Awards

Related Research Articles

<span class="mw-page-title-main">Seafloor spreading</span> Geological process at mid-ocean ridges

Seafloor spreading, or seafloor spread, is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.

<span class="mw-page-title-main">Lithosphere</span> Outermost shell of a terrestrial-type planet or natural satellite

A lithosphere is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more. The crust and upper mantle are distinguished on the basis of chemistry and mineralogy.

<span class="mw-page-title-main">Asthenosphere</span> Highly viscous, mechanically weak, and ductile region of Earths mantle

The asthenosphere is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between ~80 and 200 km below the surface, and extends as deep as 700 km (430 mi). However, the lower boundary of the asthenosphere is not well defined.

<span class="mw-page-title-main">Subduction</span> A geological process at convergent tectonic plate boundaries where one plate moves under the other

Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.

<span class="mw-page-title-main">Convergent boundary</span> Region of active deformation between colliding tectonic plates

A convergent boundary is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Wadati–Benioff zone. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.

<span class="mw-page-title-main">Island arc</span> Arc-shaped archipelago formed by intense seismic activity of long chains of active volcanoes

Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.

<span class="mw-page-title-main">Continental crust</span> Layer of rock that forms the continents and continental shelves

Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in aluminium silicates (Al-Si) and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate (Mg-Si) minerals. Changes in seismic wave velocities have shown that at a certain depth, there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character.

<span class="mw-page-title-main">Oceanic crust</span> Uppermost layer of the oceanic portion of a tectonic plate

Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere.

<span class="mw-page-title-main">Mid-ocean ridge</span> Basaltic underwater mountain system formed by plate tectonic spreading

A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin.

<span class="mw-page-title-main">Primitive mantle</span> Layer in a newly formed planet

In geochemistry, the primitive mantle is the chemical composition of the Earth's mantle during the developmental stage between core-mantle differentiation and the formation of early continental crust. The chemical composition of the primitive mantle contains characteristics of both the crust and the mantle.

Susan Y. Schwartz is a scientist at the University of California, Santa Cruz known for her research on earthquakes, through field projects conducted in locations in Costa Rica and the San Andreas Fault.

<span class="mw-page-title-main">Crustal recycling</span> Tectonic recycling process

Crustal recycling is a tectonic process by which surface material from the lithosphere is recycled into the mantle by subduction erosion or delamination. The subducting slabs carry volatile compounds and water into the mantle, as well as crustal material with an isotopic signature different from that of primitive mantle. Identification of this crustal signature in mantle-derived rocks is proof of crustal recycling.

<span class="mw-page-title-main">Lithosphere–asthenosphere boundary</span> Level representing a mechanical difference between layers in Earth’s inner structure

The lithosphere–asthenosphere boundary represents a mechanical difference between layers in Earth's inner structure. Earth's inner structure can be described both chemically and mechanically. The lithosphere–asthenosphere boundary lies between Earth's cooler, rigid lithosphere and the warmer, ductile asthenosphere. The actual depth of the boundary is still a topic of debate and study, although it is known to vary according to the environment.

<span class="mw-page-title-main">Flat slab subduction</span> Subduction characterized by a low subduction angle

Flat slab subduction is characterized by a low subduction angle beyond the seismogenic layer and a resumption of normal subduction far from the trench. A slab refers to the subducting lower plate. A broader definition of flat slab subduction includes any shallowly dipping lower plate, as in western Mexico. Flat slab subduction is associated with the pinching out of the asthenosphere, an inland migration of arc magmatism, and an eventual cessation of arc magmatism. The coupling of the flat slab to the upper plate is thought to change the style of deformation occurring on the upper plate's surface and form basement-cored uplifts like the Rocky Mountains. The flat slab also may hydrate the lower continental lithosphere and be involved in the formation of economically important ore deposits. During the subduction, a flat slab itself may deform or buckle, causing sedimentary hiatus in marine sediments on the slab. The failure of a flat slab is associated with ignimbritic volcanism and the reverse migration of arc volcanism. Multiple working hypotheses about the cause of flat slabs are subduction of thick, buoyant oceanic crust (15–20 km) and trench rollback accompanying a rapidly overriding upper plate and enhanced trench suction. The west coast of South America has two of the largest flat slab subduction zones. Flat slab subduction is occurring at 10% of subduction zones.

<span class="mw-page-title-main">Subduction polarity reversal</span>

Subduction polarity reversal is a geologic process in which two converging plates switch roles: The over-lying plate becomes the down-going plate, and vice versa. There are two basic units which make up a subduction zone. This consists of an overriding plate and the subduction plate. Two plates move towards each other due to tectonic forces. The overriding plate will be on the top of the subducting plate. This type of tectonic interaction is found at many plate boundaries.

Ridge push is a proposed driving force for plate motion in plate tectonics that occurs at mid-ocean ridges as the result of the rigid lithosphere sliding down the hot, raised asthenosphere below mid-ocean ridges. Although it is called ridge push, the term is somewhat misleading; it is actually a body force that acts throughout an ocean plate, not just at the ridge, as a result of gravitational pull. The name comes from earlier models of plate tectonics in which ridge push was primarily ascribed to upwelling magma at mid-ocean ridges pushing or wedging the plates apart.

<span class="mw-page-title-main">Marine geophysics</span>

Marine geophysics is the scientific discipline that employs methods of geophysics to study the world's ocean basins and continental margins, particularly the solid earth beneath the ocean. It shares objectives with marine geology, which uses sedimentological, paleontological, and geochemical methods. Marine geophysical data analyses led to the theories of seafloor spreading and plate tectonics.

Rachel Abercrombie is a seismologist at Boston University known for her research on the process of earthquake ruptures.

Anne Sheehan is a geologist known for her research using seismometer data to examine changes in the Earth's crust and mantle.

Donna Eberhart-Phillips is a geologist known for her research on subduction zones, especially in Alaska and New Zealand.

References

  1. 1 2 3 Fischer, Karen Marie (1989). The morphology and dynamics of subducting lithosphere (Thesis thesis). Massachusetts Institute of Technology. hdl:1721.1/57820.
  2. 1 2 3 "Fischer, Karen". vivo.brown.edu. Retrieved 2021-06-03.
  3. ↑ "Karen Fischer | IRIS". www.iris.edu. Retrieved 2021-06-03.
  4. ↑ "Geochemistry, Geophysics, Geosystems". AGU Journals. Retrieved 2021-06-03.
  5. ↑ "About - Seismology". connect.agu.org. Retrieved 2021-06-03.
  6. ↑ Fischer, Karen M.; Ford, Heather A.; Abt, David L.; Rychert, Catherine A. (2010-04-01). "The Lithosphere-Asthenosphere Boundary". Annual Review of Earth and Planetary Sciences. 38 (1): 551–575. doi:10.1146/annurev-earth-040809-152438. ISSN   0084-6597.
  7. ↑ Fischer, Karen M.; McNutt, Marcia K.; Shure, Loren (1986). "Thermal and mechanical constraints on the lithosphere beneath the Marquesas swell". Nature. 322 (6081): 733–736. doi:10.1038/322733a0. ISSN   1476-4687. S2CID   4350676.
  8. ↑ Fischer, Karen M.; Jordan, Thomas H. (1991). "Seismic strain rate and deep slab deformation in Tonga". Journal of Geophysical Research: Solid Earth. 96 (B9): 14429–14444. doi:10.1029/91JB00153. ISSN   2156-2202.
  9. ↑ Fischer, Karen M.; Parmentier, E. M.; Stine, Alexander R.; Wolf, Elizabeth R. (2000). "Modeling anisotropy and plate-driven flow in the Tonga subduction zone back arc". Journal of Geophysical Research: Solid Earth. 105 (B7): 16181–16191. doi:10.1029/1999JB900441. ISSN   2156-2202. S2CID   18657537.
  10. ↑ Smith, G. P.; Wiens, Douglas A.; Fischer, Karen M.; Dorman, Leroy M.; Webb, Spahr C.; Hildebrand, John A. (2001-04-27). "A Complex Pattern of Mantle Flow in the Lau Backarc". Science. 292 (5517): 713–716. doi:10.1126/science.1058763. PMID   11326095. S2CID   4822268.
  11. ↑ Fischer, Karen M.; Purdy, G. M. (1986). "Seismic amplitude modeling and the shallow crustal structure of the East Pacific Rise at 12°N". Journal of Geophysical Research: Solid Earth. 91 (B14): 14006–14014. doi:10.1029/JB091iB14p14006. ISSN   2156-2202.
  12. ↑ Li, Aibing; Fischer, Karen M.; Wysession, Michael E.; Clarke, Timothy J. (1998). "Mantle discontinuities and temperature under the North American continental keel". Nature. 395 (6698): 160–163. doi:10.1038/25972. ISSN   1476-4687. S2CID   4420431.
  13. 1 2 "Speaker series". EarthScope.
  14. ↑ Parker, E. Horry; Hawman, Robert B.; Fischer, Karen M.; Wagner, Lara S. (2013). "Crustal evolution across the southern Appalachians: Initial results from the SESAME broadband array". Geophysical Research Letters. 40 (15): 3853–3857. doi: 10.1002/grl.50761 . ISSN   1944-8007.
  15. ↑ "How a continent collision built the Appalachian mountains". Futurity. 2016-11-22. Retrieved 2021-06-03.
  16. ↑ Hall, Galen (2016-12-02). "Brown researchers investigate birth of Appalachian mountains". Brown Daily Herald. Retrieved 2021-06-03.
  17. ↑ Fischer, Karen M. (2002). "Waning buoyancy in the crustal roots of old mountains". Nature. 417 (6892): 933–936. doi:10.1038/nature00855. ISSN   1476-4687. PMID   12087400. S2CID   4424777.
  18. ↑ Li, Aibing; Fischer, Karen M.; Lee, Suzan van der; Wysession, Michael E. (2002). "Crust and upper mantle discontinuity structure beneath eastern North America". Journal of Geophysical Research: Solid Earth. 107 (B5): ESE 7–1–ESE 7–12. doi: 10.1029/2001JB000190 . ISSN   2156-2202.
  19. ↑ Rychert, Catherine A.; Fischer, Karen M.; Rondenay, Stéphane (2005). "A sharp lithosphere–asthenosphere boundary imaged beneath eastern North America". Nature. 436 (7050): 542–545. doi:10.1038/nature03904. ISSN   1476-4687. PMID   16049485. S2CID   4386941.
  20. ↑ Lekic, V.; French, S. W.; Fischer, K. M. (2011-11-11). "Lithospheric Thinning Beneath Rifted Regions of Southern California". Science. 334 (6057): 783–787. doi: 10.1126/science.1208898 . ISSN   0036-8075. PMID   21979933. S2CID   19422684.
  21. ↑ Hu, Jiashun; Liu, Lijun; Faccenda, Manuele; Zhou, Quan; Fischer, Karen M.; Marshak, Stephen; Lundstrom, Craig (2018). "Modification of the Western Gondwana craton by plume–lithosphere interaction". Nature Geoscience. 11 (3): 203–210. doi:10.1038/s41561-018-0064-1. ISSN   1752-0894. S2CID   134835402.
  22. ↑ Yoksoulian, Lois. "Continental interiors may not be as tectonically stable as geologists think". news.illinois.edu. Retrieved 2021-06-03.
  23. ↑ Hopper, Emily; Fischer, Karen M. (2018). "The Changing Face of the Lithosphere-Asthenosphere Boundary: Imaging Continental Scale Patterns in Upper Mantle Structure Across the Contiguous U.S. With Sp Converted Waves". Geochemistry, Geophysics, Geosystems. 19 (8): 2593–2614. doi: 10.1029/2018GC007476 . ISSN   1525-2027.
  24. 1 2 "Karen Fischer | Seismological Society of America". www.seismosoc.org. Retrieved 2021-06-03.
  25. ↑ Anonymous (2010). "AGU Fellows Elected for 2010". Eos, Transactions American Geophysical Union. 91 (6): 59. doi: 10.1029/2010EO060010 . ISSN   2324-9250.
  26. ↑ "2016 AGU Section and Focus Group Awardees and Named Lecturers". Eos. Retrieved 2021-06-03.
  27. ↑ "Karen Fischer wins top honor in seismology". EurekAlert!. Retrieved 2021-06-03.
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