David G. Harkrider, professor of geophysics, emeritus, at Caltech and an expert in seismological wave propagation, passed away on Tuesday, February 16, 2016. He was 84.
Born on September 25, 1931 in Houston, Texas, Harkrider received his bachelor’s and master’s degrees from Rice University in 1953 and 1957, respectively. He earned a doctorate in geophysics from Caltech in 1963 and remained as a research fellow until 1965, when he joined the Department of Geology at Brown University as an assistant professor. Harkrider returned to Caltech as an associate professor in 1970, becoming a professor in 1979 and a professor emeritus in 1995. From 1977–1979 he was the associate director of Caltech’s Seismological Laboratory.
He was elected a Fellow of the American Geophysical Union in 1979. From 1982–1988 he was on the board of the Seismological Society of America, serving as vice president in 1987 and as president in 1988. He was elected a Fellow of the Royal Astronomical Society in 2009.
Harkrider investigated diverse topics within the field of geophysics. Early in his career he studied the theory of air-wave trains—the oscillations of the atmosphere in regions experiencing strong shocks, such as a meteor or a nuclear explosion. At Caltech, he collaborated with Professor of Geophysics Donald Helmberger and then-Professor of Geophysics Charles Archambeau (now a retired professor of physics at the University of Colorado) to analyze and interpret the propagation of seismic waves in the earth. Harkrider’s work was focused on the analysis of the propagation of surface waves—a type of seismic wave that travels through the crust—and their coupling with air waves and tsunami waves. He led the development of a digital computing system to recognize the seismic signals from earthquakes, rapidly determine their locations, and distinguish the signatures of earthquakes from those of nuclear explosions. Harkrider’s modeling efforts played a key role in ensuring the compliance of the Nuclear Test Ban Treaty with the Soviet Union.
Together with Don Helmberger, Harkrider taught a year-long course in seismology. Numerous graduates of the program went on to pursue PhDs in the field and are now professors.
“David took surface-wave theory from the rather primitive state in which it existed in the late 1960’s to the point where a generalized seismic source could be embedded at any depth in an arbitrarily layered media and the response, including synthetic seismograms, calculated,” says Professor of Geophysics Robert W. Clayton. “He was pioneer in the application of computer techniques to seismological problems.”
“Although Harkrider’s most widely known published works are on the excitation and propagation of surface waves in multi-layered media, his handwritten class notes on propagation of acoustic-gravity waves were very useful for seismologists who ventured into the field of acoustic-gravity waves from seismic waves,” says Hiroo Kanamori, the John E. and Hazel S. Smits Professor of Geophysics, emeritus, and Harkrider’s longtime colleague. “When I became interested in acoustic-gravity waves after the large eruption of Mount Pinatubo in 1991, I studied his class notes in great detail. These notes are so unique that I am sure that many students must have benefitted a great deal from them. I wish they were published.”
Harkrider, his family notes, was a “kind and generous man with a sharply irreverent wit who loved his family, his friends, his cats and dogs, and his research,” and enjoyed football, golf, old musicals, Mexican food, martinis, and “Tabasco on everything.” He is survived by his wife, Sara Brydges; daughter, Claire Harkrider Topp; son, John D. Harkrider; and by four grandchildren.
The idea that the wholesale relocation of Earth’s continents 520 million years ago, also known as “true polar wander,” coincided with a burst of animal speciation in the fossil record dates back almost 20 years to an original hypothesis by Joseph Kirschvink (BS, MS ’75), Caltech’s Nico and Marilyn Van Wingen Professor of Geobiology, and his colleagues. For more than a century, paleontologists including Charles Darwin have debated whether the so-called Cambrian explosion—a rapid period of species diversification that began around 542 million years ago—was the equivalent of an evolutionary “big bang” of biological innovation, or just an artifact of the incomplete fossil record.
In a new study published in the December issue of the American Journal of Science, a team of researchers including Kirschvink and Ross Mitchell, a postdoctoral scholar in geology at Caltech, describes a new computer model showing that during the proposed Cambrian true polar wander event, most continents would have moved toward the equator instead of toward the poles.
“It’s long been observed that biological diversity is highest in the tropics, where nutrients and energy tend to be abundant,” says Kirschvink. “One of the side effects of true polar wander is that sea level rises near the equator but falls near the poles, so the equatorial migration of most Cambrian land masses would have enhanced diversification into previously lower-diversity environments.”
Using a computer model they developed, the team simulated the pattern of continental migration during the Cambrian and found that their results can explain the distribution of Cambrian fossils.
“Our model provides an explanation for why the fossil record looks the way it does, with many Cambrian fossil groups on some continents but few on others,” says study coauthor Tim Raub (BS, MS ’02), a lecturer at the University of St. Andrews in Scotland.
“The same sea-level rise which flooded those continents that shifted to the tropics and opened new ecological niches for faster speciation also led to more fossil preservation,” Mitchell says. “In contrast, the few areas that shifted to the poles became less biologically diverse and also lost rock volume to erosion following sea-level drops due to true polar wander.”
The scientists say their new findings could help resolve the debate started so long ago by Darwin. If their theory is correct, the Cambrian explosion is both a true and dramatic pulse of biological innovation and an expression of preferentially preserved shells on selectively submerged continental margins capable of containing fossils.
Funding for the study was provided by the National Science Foundation.
Dianne Newman, professor of biology and geobiology at Caltech and an investigator with the Howard Hughes Medical Institute, has been awarded the National Academy of Sciences (NAS) Award in Molecular Biology for her “discovery of microbial mechanisms underlying geologic processes.” The award citation recognizes her for “launching the field of molecular geomicrobiology” and fostering greater awareness of the important roles microorganisms have played and continue to play in how Earth evolved.
“Trust me, no one was more shocked than I was by this news,” says Newman. “It really honors the many the exceptional people who have come through my lab over the years, as well as the geobiology field more broadly. Geobiology is a venerable old field, which offers many fascinating and important problems that would benefit from the attention of individuals trained in mechanistic research. Hopefully this award will encourage more young people from molecular and cellular biology to enter the field.”
Newman’s research focuses on the relationship between microorganisms and geologic processes. She has demonstrated that some bacteria in iron-rich environments, such soils and sediments, can utilize extracellular iron as a dump site for excess electrons by generating extracellular electron shuttles, including a class of metabolites formerly considered to be redox-active antibiotics. Newman has also made contributions to our understanding of other microbial metabolic processes of geological significance, including how microbes respire using arsenate instead of oxygen, and how they perform photosynthesis using iron rather than water. In addition, she and her coworkers have studied the mechanisms by which certain microbes make stromatolites and magnetosomes, two types of structures that leave biosignatures in ancient rocks. Perhaps most importantly, her team has demonstrated the power of applying genetic analysis to diverse organisms from iron-rich environments, paving the way for others to do the same.
Newman is now hoping to bring tools commonly used in geochemistry to facilitate environmentally-informed studies of pathogens in chronic infections. For example, in collaboration with Caltech professor of geobiology Alex Sessions and researchers at Children’s Hospital Los Angeles, Newman’s group has characterized the composition and growth rate of pathogens in mucus collecting in the lungs of individuals with cystic fibrosis. Using this information, her lab is designing new experiments to reveal the survival mechanisms utilized by microorganisms—such as Pseudomonas aeruginosa, an opportunistic bacterium that colonizes the lungs of these patients—in this environment.
The NAS Award in Molecular Biology was first given in 1962. It is presented with a medal and a $ 25,000 prize. Newman will receive the award on May 1, 2016, during the National Academy of Sciences’ annual meeting in Washington, D.C.
Previous recipients of the award include David Baltimore, Caltech President Emeritus and the Robert Andrews Millikan Professor of Biology.
Since the late 1970s, Caltech seismologist Tom Heaton, professor of engineering seismology, has been working to develop earthquake early-warning (EEW) systems—networks of ground-based sensors that can send data to users when the earth begins to tremble nearby, giving them seconds to potentially minutes to prepare before the shaking reaches them. In fact, Heaton wrote the first paper published on the concept in 1985. EEW systems have been implemented in countries like Japan, Mexico, and Turkey. However, the Unites States has been slow to regard EEW systems as a priority for the West Coast.
But on February 2, 2016, the White House held the Earthquake Resilience Summit, signaling a new focus on earthquake safety and EEW systems. There, stakeholders—including Caltech’s Heaton and Egill Hauksson, research professor in geophysics; and U.S. Geological Survey (USGS) seismologist Lucy Jones, a visiting associate in geophysics at Caltech and seismic risk advisor to the mayor of Los Angeles—discussed the need for earthquake early warning and explored steps that can be taken to make such systems a reality.
At the summit, the Gordon and Betty Moore Foundation announced $ 3.6 million in grants to advance a West Coast EEW system called ShakeAlert, which received an initial $ 6 million in funding from foundation in 2011. The new grants will go to researchers working on the system at Caltech, the USGS, UC Berkeley, and the University of Washington.
“We have been successfully operating a demonstration system for several years, and we know that it works for the events that have happened in the test period,” says Heaton. “However, there is still significant development that is required to ensure that the system will work reliably in very large earthquakes similar to the great 1906 San Francisco earthquake. This new funding allows us to accelerate the rate at which we develop this critical system.”
In addition, the Obama Administration outlined new federal commitments to support greater earthquake safety including an executive order to ensure that new construction of federal buildings is up to code and that federal assets are available for recovery efforts after a large earthquake.
The commitments follow a December announcement from Congressman Adam Schiff (D-Burbank) that Congress has included $ 8.2 million in the fiscal year 2016 funding bill specifically designated for a West Coast earthquake early warning system.
“By increasing the funding for the West Coast earthquake early-warning system, Congress is sending a message to the Western states that it supports this life-saving system. But the federal government cannot do it alone and will need local stakeholders, both public and private, to get behind the effort with their own resources,” said Schiff, in a press release. “The early warning system will give us critical time for trains to be slowed and surgeries to be stopped before shaking hits—saving lives and protecting infrastructure. This early warning system is an investment we need to make now, not after the ‘big one’ hits.”
ShakeAlert utilizes a network of seismometers—instruments that measure ground motion—widely scattered across the Western states. In California, that network of sensors is called the California Integrated Seismic Network (CISN) and is made up of computerized seismometers that send ground-motion data back to research centers like the Seismological Laboratory at Caltech.
Here’s how the current ShakeAlert works: a user display opens in a pop-up window on a recipient’s computer as soon as a significant earthquake occurs in California. The screen lists the quake’s estimated location and magnitude based on the sensor data received to that point, along with an estimate of how much time will pass before the shaking reaches the user’s location. The program also gives an approximation of how intense that shaking will be. Since ShakeAlert uses information from a seismic event in progress, people living near the epicenter do not get much—if any—warning, but those farther away could have seconds or even tens of seconds’ notice.
The goal is an improved version of ShakeAlert that will eventually give schools, utilities, industries, and the general public a heads-up in the event of a major temblor.
Read more about how ShakeAlert works and about Caltech’s development of EEW systems in a feature that ran in the Summer 2013 issue of E&S magazine called Can We Predict Earthquakes?
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