EARTH 520
Plate Tectonics and People

Thomas Jordan

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Biographic Information

Coco Solo was a United States Navy submarine base and naval air station on the Atlantic Ocean side of the Panama Canal Zone. It was here that, on October 8, 1948, one of the biggest contributors to our understanding of Earth’s interior was born. Today, Thomas H. Jordan can be found on the Pacific Ocean side at the University of Southern California.

It is no surprise that someone fascinated by earthquakes found his way to the tectonically active state of California. In fact, Tom Jordan became pretty comfortable with the state while earning all three of his degrees. He received a BS in geophysics from the California Institute of Technology in 1969 and immediately followed with his Masters degree. In 1972,  he earned a doctorate in geophysics and applied mathematics also from the California Institute of Technology.

Tectonic Trivia: Earthquakes happen constantly in California, where Dr. Jordan lives. Go to this map.
Do you notice a pattern of earthquake location? Have any earthquakes happened in the last hour?                                                                                                                                                                                                                             (scholar.google.com)

Dr. Jordan then headed to the east coast as he filled professorships at Princeton University, Scripps Institution of Oceanography, and the Massachusetts Institute of Technology. While at MIT, he served as the head of the Department of Earth, Atmosphere and Planetary Sciences from 1988-1998. In 2000, he jumped back to the west coast to be a professor at the University of Southern California.

Currently serving as the director of the Southern California Earthquake Center (SCEC), Dr. Jordan leads a research program that involves over 600 scientists at more than 60 universities.


Contributions to plate tectonic theory and/or geophysics

Dr. Jordan’s contributions to understanding Earth’s interior are as varied and in depth as earthquakes themselves.

Because we can’t peer beneath the crust, geophysicists have developed clever strategies to “look” inside Earth by using earthquake waves. Much of Jordan’s work has been possible due to his revolutionary efforts in developing new techniques for measuring and visualizing Earth’s interior (ex. Jordan 1975, Jordan 1978)

Tectonic Trivia: Using earthquake waves to analyze Earth’s interior is called seismic tomography. Go here to read about the basics of this process. How are earthquake waves used to image Earth’s interior? What is one complication of this technique?

While the edges of tectonic plates are constantly recycled and transformed, some interior parts have stayed relatively stable over Earth’s history. These pieces, called cratons, are thicker parts of the crust that represent billions of years (see image below). The strength and thickness of the cratonic crust stems from the craton keel that lies underneath (Grotzinger and Jordan 2003). The keel of the crust is composed of lithospheric mantle and is given a separate name because of its distinctive chemical properties (i.e. containing less dense minerals). 

                      
                         (nature.com)

By developing new techniques, Jordan was able to measure the keels in continental cratons and discover properties of these keels (Creager and Jordan 1986). Jordan concluded that the average thickness of cratonic crust is unlikely to be less than 300 km, which means the keel could fill the entire upper mantle. This estimate was larger than what was previously suggested, which altered our view on the formation and evolution of the continents. 

Digging even deeper, Jordan and his students also explored the workings of mantle convection. A question that remained in the early days of plate tectonic theory was whether mantle convection happened as a whole or as layers. Better tomographic imaging revealed to Jordan that lithospheric slabs actually penetrate into the lower mantle. This drastically improved our understanding of mantle convection. Later, Jordan helped explain the Lehmann and Gutenberg discontinuities by developing new methods for imaging mantle structure.

In 1978, Jordan and JB Minster published a paper on plate motions that inverted 110 spreading rates, 78 transform fault azimuths, and 142 earthquake slip vectors (Jordan and Minster 1978). This paper established a new plate motion model, RM2, which has become a standard in the field.

In 2007, Dr. Jordan and his students dived into the crust beneath their own feet in Los Angeles and published the first regional Earth models derived by “full-3D” tomography (Chen et al. 2007). 

Jordan has truly served as one of our most important set of eyes peering into the Earth.

Tectonic Trivia: Dr. Jordan and his students are pros at visualizing the abstract motion of Earth’s interior. Go here to watch a simulation of a possible M8 earthquake on the San Andreas Fault made by the SCEC. What patterns do you notice? Can you think of an analogy to describe the energy movement? 


Other scientific contributions

Dr. Jordan:

  • Established the International Collaboratory for the Study of Earthquake Predictability in 2006.
  • Published extensively on techniques for earthquake forecasting and forecast evaluation, including a major study by the International Commission on Earthquake Forecasting, which he chaired.
  • Chaired the NRC panels that produced two decadal reports.
  • Published two textbooks, contributed to several book chapters, and published over 200 scientific articles. 
  • Led an interdisciplinary team that conducted the largest earthquake simulation on the world’s fastest computer in 2010. At right is an image from this project. Click here for more visualizations from the M8 simulation.
                                                                                                                                       (visservices.sdsc.edu)

Other cool stuff you should know

Dr. Jordan has been widely recognized for his contributions to the geosciences.

Awards:

  • Woollard Award and President’s Medal of the Geological Society of America
  • 2012 Award for Outstanding Contribution to Public Understanding of the Geosciences by the American Geosciences Institute
  • Macelwane and Lehmann Medals of the American Geophysical Union

Elected member of the:

  • National Academy of Sciences
  • American Academy of Arts and Sciences
  • American Philosophical Society

Tectonic Trivia: Google Scholar keeps track of a scientist’s contributions, including the history of Dr. Jordan’s publications and citations. Go here to check out his impressive stats! Let’s do a fun calculation to understand Dr. Jordan’s contribution to science. The theory of plate tectonics arose around 1968. About how many days have passed since then? How does that number compare to the number of times Dr. Jordan’s work has been cited? 

 

Bibliography

Chen, P., Zhao, L., Jordan, T. H. (2007). Full 3D tomography for crustal structure of the Los Angeles region. Bulletin of the Seismological Society of America. Vol. 97, pp. 1094-1120.

Creager, K. C., Jordan, T. H. (1986). Slab penetration into the lower mantle beneath the Mariana and other island arcs of the northwest Pacific. Journal of Geophysical Research-Solid Earth and Planets. Vol. 91 (B3), pp. 3573-3589.

Grotzinger, J., Jordan, T. H. (2010). Understanding Earth, 6th Ed. New York: W. H. Freeman.

Jordan, T. H. (1975). The continental tectosphere. Reviews of Geophysics.

Jordan, T. H. (1978). Composition and development of the continental tectosphere. Nature. Vol. 274 (5671), pp. 544-548.

Minster, J. B., Jordan, T. H. (1978). Present-day plate motions. Journal of Geophysical Research. Vol. 83 (NB11), pp. 5331-5354.

Nyblade, A. A. (2001). Earth science: Hard-cored continents. Nature Vol. 411, pp. 38-29.

Southern California Earthquake Center

University of Southern California Faculty Profile

Answers: 
1. The earthquakes do follow a curved pattern that represents the plate boundary below which the earthquakes commonly (but not all) occur. There is usually at least a few earthquakes mapped that have taken place in the last hour!
2. If the Earth had the same composition throughout it's interior, seismic waves would travel a straight path. However, the waves seem to refract and bend during their journey. This is measured based off of when the seismic waves arrive at stations around the globe. Because of this curved trajectory and the since waves can bounce off of certain boundaries, this technique is very complicated and a huge work in progress. 
3. The waves follow a distinct rippling pattern as they travel in all directions from the energy source. The pattern seems to be predictable and measureable. This rippling is similar to a rock being thrown in a pond. 
4. About 46 years and 16,790 days have passed since the theory arose. Dr. Jordan has over 16,600 citations. Almost one for everday the theory has been around! Amazing!