NSF Awards $2.16 Million for Intraplate Earthquake Studies


Among the many mysteries of our planet’s geology is why earthquakes occur in the middle of presumably stable tectonic plates. A project led by a group of University of Missouri-Columbia researchers has been awarded $2.16 million from the National Science Foundation (NSF) to bolster the collaborative efforts between the U.S. and China in determining the cause of intraplate earthquakes that have occurred in both countries.



Mian Liu, professor of geophysics in the College of Arts and Science, leads this multi-institutional study with a team of colleagues from MU’s Department of Geological Sciences. Those colleagues are: Associate Professor Eric Sandvol and Assistant Professors Francisco (Paco) Gomez and Milene Cormier. The MU team will work with its U.S. and Chinese partners to explore the fundamental physics that control intraplate earthquakes. Knowledge gained from North China will help in understanding earthquakes in the New Madrid area and other seismic zones in central and eastern U.S., as well as benefit the broader geosciences community through the production of data sets, computer models and curriculum materials.



“This is not a research project in the traditional sense,” Liu said. “Through the collaborative research, we want to provide our students with a unique international experience.”



Unlike interplate earthquakes in California and many other places where the earth’s crust is stressed by the relative motion of tectonic plates, which are pieces of the Earth’s rigid outer shell, intraplate quakes happen in the middle of presumably stable tectonic plates and thus cannot be readily explained. In the past seven centuries, more than 50 large earthquakes have struck North China. On July 28, 1976, a magnitude 7.6 earthquake killed 244,000 people and nearly wiped out the industrial city of Tangshan, about 200 miles southeast of Beijing. Intraplate earthquakes in the U.S. have not been as frequent but have been severe. In 1811 and 1812, a series of large earthquakes with estimated magnitudes above 7.0 occurred on the New Madrid faults in southeastern Missouri within the span of three months. The region remains seismically active today.



Liu and the MU team have been working with Chinese colleagues in a pilot study of North China earthquakes in recent years. This PIRE (Partnerships for International Research and Education) project will build a broad partnership to investigate what causes large intraplate quakes in North China and improve understanding of intraplate seismic activity in central and eastern United States. The U.S. partners include the University of Oklahoma, University of Colorado, North Carolina State University, U.S. Geological Survey, the Incorporated Research Institutions for Seismology (IRIS), and UNAVCO. The Chinese partners include two top Chinese universities, the Chinese Academy of Sciences and the China Earthquake Administration.


“PIRE is a new NSF program intended to strengthen collaboration between U.S. and international institutions,” Liu said. “The long-term goal is to educate and train a new generation of globally engaged American scientists and engineers.”



About 15 graduate students, 20 undergraduate students and 50 science teachers from the Midwestern states around the New Madrid seismic region will participate in this project. Lloyd Barrow, professor of science education in MU’s College of Education, will assist the educational and outreach activity.



Underrepresented minority students will be recruited, and most student participants will travel to China to work with Chinese students and scientists. Liu said that this is a great time to collaborate with China on earthquake studies. In recent years, China has infused large amounts of equipment and funds into earthquake research that has caught the attention of the international geosciences community. This year, the National Science Foundation of China launched an ambitious research initiative with $20 million to study earth structure and earthquakes in North China. For this PIRE project, the Chinese partners will provide most of the field equipment, logistical support, and complementary expertise.



“MU has shown a very strong institutional support and commitment to this project,” Liu said. “We’ve received a lot of support and a lot of resources from the University community, and we hope to bring long-term benefit of international collaboration to our campus and community through this partnership. We want to better understand this type of earthquakes, because it’s particularly important to the state of Missouri.”

For earthquakes ‘speed kills’


High-speed ruptures travelling along straight fault lines could explain why some earthquakes are more destructive than others, according to an Oxford University scientist. In this week’s Science, Professor Shamita Das suggests that ruptures in the Earth’s surface moving at 6km per second could make future earthquakes along California’s San Andreas fault much more destructive than current models predict.



Professor Das compared data from the 1906 California earthquake with data from a similar earthquake that occurred in 2001 in Kunlunshan, Tibet. The comparison suggests that, in both, the long straight portions of the fault enabled ruptures to travel twice as fast as the original ‘shear’ wave travelling through the rock. Such ‘super-shear’ waves were once thought to be impossible but could now explain why similar magnitudes of earthquake can cause much greater devastation in some areas than others.



“Long straight faults are more likely to reach high rupture speeds,” said Professor Das of the Department of Earth Sciences. “The fault starts from rest, then accelerates to the maximum permissible speed and continues at this speed until it reaches an obstacle such as a large ‘bend’. If the next earthquake in southern California follows the same pattern as the ones in California in 1857 and 1906, and in Tibet in 2001, a super-shear rupture travelling southward would strongly focus shock waves on Santa Barbara and Los Angeles.”


The 2001 Kunlunshan earthquake is of particular interest to scientists because it was so well preserved owing to its remote location and dry desert environment. Studies of the earthquake revealed telltale off-fault open cracks only at the portions where it was found to have a very high rupture speed. “These cracks confirm that the earthquake reached super-shear speeds on the long, straight section of the fault. This is the first earthquake where such direct evidence is available and it is exactly the kind of evidence that we do not have for the similar earthquake in California 1906, due to the heavy rains and rapid rebuilding that occurred there immediately afterwards.”



Professor Das believes that future research into rupture speeds could take scientists one step closer to predicting the potential impact of earthquakes in particular regions. She commented: “It appears that the 1857 and 1906 California earthquakes may have propagated faster than was previously thought. If this is the case then we need to apply the same analysis to other similar faults around the world. By developing a measure of the ‘straightness’ of faults and finding and recording evidence such as off-fault open cracks we hope to better understand these potentially devastating phenomena.” The full article, entitled ‘The Need to Study Speed’, is published in Science on 17 August 2007.

2006 Plate Motion Reversal Unlikely To Have Eased Seismic Strain, Earthquake Anticipation Near Acapulco





A reversal of tectonic plate motion near Acapulco, Mexico, in 2006 (colored arrows) as measured by GPS satellites did little to ease seismic strain in the region and the potential for a large earthquake that could impact Mexico City 175 miles away, according to a new study led by CU-Boulder.
A reversal of tectonic plate motion near Acapulco, Mexico, in 2006 (colored arrows) as measured by GPS satellites did little to ease seismic strain in the region and the potential for a large earthquake that could impact Mexico City 175 miles away, according to a new study led by CU-Boulder.

A reversal of tectonic plate motion between Acapulco and Mexico City in the last half of 2006 probably didn’t ease seismic strain in the region or the specter of a major earthquake anticipated there in the coming decades, says a University of Colorado at Boulder professor.



Instead of creeping toward Mexico City at about one inch per year – the expected speed from plate tectonic theory – the region near Acapulco moved in the opposite direction for six months and sped up by four times, said CU-Boulder aerospace engineering Professor Kristine Larson. The changes in motion were detected by analyzing data from GPS satellite receivers set up in Guerrero, Mexico, that were installed by the National Autonomous University of Mexico (UNAM) under the direction of UNAM geophysicist Vladimir Kostoglodov and augmented by CU-Boulder.



“The million-dollar question is whether the event makes a major earthquake in the region less likely or more likely,” said Larson, whose research is funded in part by the National Science Foundation. “So far, it does not appear to be reducing the earthquake hazard.”



A paper on the subject by Larson, the University of Tokyo’s Shin’ichi Miyazaki and UNAM’s Kostoglodov and José Antonio Santiago was published Aug. 1 in Geophysical Research Letters.



Scientists use GPS satellite receivers to record laser pulses from spacecraft to measure tiny movements in Earth’s crust.



The question of earthquake hazard is particularly important for Guerrero, since it is located 175 miles southwest of Mexico City, Larson said. “A very large earthquake in Guerrero would produce seismic waves that would travel quickly to the Mexican capital, and since Mexico City is built on water-saturated lakebed deposits that amplify seismic energy, the results would be catastrophic,” she said.


In 1985, a magnitude 8.1 earthquake triggered by the Cocos Plate dipping under the North American Plate off the west coast of southern Mexico struck along the coast north of Guerrero and killed 10,000 people in Mexico City, injured about 50,000 and caused an estimated $5 billion in property damage.



Since the last major earthquake in northwest Guerrero was a 7.6 magnitude event in 1911, many scientists think the area is ripe for a much larger earthquake, likely in the range of 8.1 to 8.4, Larson said. Geophysicists refer to the impending earthquake as the “Guerrero Gap,” she said.



“Before GPS we thought the ground moved at a constant speed between earthquakes,” Larson said. “The recognition of these transient events where the plate reverses direction is arguably the most important geophysical discovery that has stemmed from the introduction of GPS measurements.”



The Guerrero slip events recorded by Larson and Kostoglodov’s research team in 2006 are the largest ever reported in the world.



Studies of the Guerrero Gap are helping scientists better understand other subduction zones around the world, including the Cascadia region off the coast of Washington and Oregon, Larson said. Smaller but much faster backwards slip events have occurred there, as have very large earthquakes in previous centuries.

Alaskan Earthquake In 2002 Set Off Tremors On Vancouver Island





Alaskan Coast Line - Photo Credit: Web Doodle, LLC
Alaskan Coast Line – Photo Credit: Web Doodle, LLC

Perhaps it was just a matter of sympathy, but tremors rippled the landscape of Vancouver Island, the westernmost part of British Columbia, in 2002 during a major Alaskan earthquake. Geoscientists at the University of Washington have found clear evidence that the two events were related.



Tremor episodes have long been observed near volcanoes and more recently around subduction zones, regions where the Earth’s tectonic plates are shifting so that one slides beneath another. Tremors in subduction zones are associated with slow-slip events in which energy equivalent to a moderate-sized earthquake is released in days or weeks, rather than seconds.



Now researchers studying seismograph records have pinpointed five tremor bursts on Vancouver Island on Nov. 3, 2002, the result of a magnitude 7.8 earthquake on the Denali fault in the heart of Alaska.



As surface waves, called Love waves, shook Vancouver Island they triggered tremors underneath the island in the subduction zone where the Explorer tectonic plate slides beneath the North American plate. The tremors were measured by seismometers along roughly the northern two-thirds of the island.



“What we found is that when the waves pushed the North American plate to the southwest, the tremor episode turned on and when the motion reversed it turned off,” said Justin Rubinstein, a UW postdoctoral researcher in Earth and space sciences and lead author of a paper describing the work published in the Aug. 2 edition of Nature.



Though the Denali quake was mostly felt in Alaska, its effects were apparent thousands of miles away. It sloshed lakes from Seattle to Louisiana, muddied wells as far east as Pennsylvania and triggered small earthquakes in seismic zones across the Western United States.



Still, finding evidence of tremors on Vancouver Island was unusual.



“A few people have seen tremor episodes triggered by earthquakes, but not as clearly as we have. This is by far the clearest and easiest to interpret,” said co-author John Vidale, a UW professor of Earth and space sciences and director of the Pacific Northwest Seismic Network.



“This shows us it’s just like a regular fault — you add stress and it slips,” Vidale said. “It’s like regular faulting but on a different time scale.”



Other authors are Joan Gomberg of the U.S. Geological Survey in Seattle and UW researchers Paul Bodin, Kenneth Creager and Stephen Malone.



An earthquake typically will appear suddenly on a seismograph, while the much more subtle ground motion from a tremor burst gradually emerges from the background noise and then fades again, Rubinstein said.



By comparison, tremors typically produce the strongest seismic signals in a slow-slip event, in which seismic energy is released very gradually during periods as long as three weeks.


In this case, the authors suggest that the force of the Love waves induced slow slip on the interface between the North American and Explorer tectonic plates near Vancouver Island and triggered the tremor bursts, each lasting about 15 seconds.



“That made it easier for us to observe because there were these five distinct bursts,” Rubinstein said. “Normally you are not going to feel these tremors. The shaking in the tremors we observed was 1,000 times smaller than the surface waves from the earthquake.”



Being able to spot the tremors was largely a matter of distance and timing, Vidale said.



“We were able to separate the tremor signal from that of the distant earthquake because the surface waves had traveled more than 1,200 miles, losing the high-frequency vibrations that would have masked the high-frequency tremor vibrations,” Vidale said.



While the tremors were recorded a great distance from the rupture that triggered the Denali earthquake, the scientists suggest the same process could occur closer to the fault and might actually be important in the rupture process.



Seismograph data for the research came from the Canadian National Seismograph Network and was distributed by the Geological Survey of Canada.

Fragmented Structure of Seafloor Faults May Dampen Effects of Earthquakes





This bathymetric map of the seafloor shows the Siqueiros transform fault in the eastern Pacific Ocean, illustrating the fragmented structure of the fault line. (Jian Lin, Jack Cook, and Patricia Gregg, Woods Hole Oceanographic Institution)
This bathymetric map of the seafloor shows the Siqueiros transform fault in the eastern Pacific Ocean, illustrating the fragmented structure of the fault line. (Jian Lin, Jack Cook, and Patricia Gregg, Woods Hole Oceanographic Institution)

Many earthquakes in the deep ocean are much smaller in magnitude than expected. Geophysicists from the Woods Hole Oceanographic Institution (WHOI) have found new evidence that the fragmented structure of seafloor faults, along with previously unrecognized volcanic activity, may be dampening the effects of these quakes.



Examining data from 19 locations in the Atlantic, Pacific, and Indian oceans, researchers led by graduate student Patricia Gregg have found that “transform” faults are not developing or behaving as theories of plate tectonics say they should. Rather than stretching as long, continuous fault lines across the seafloor, the faults are often segmented and show signs of recent or ongoing volcanism. Both phenomena appear to prevent earthquakes from spreading across the seafloor, thus reducing their magnitude and impact.



Gregg, a doctoral candidate in the MIT/WHOI Joint Program in Oceanography and Oceanographic Engineering, conducted the study with seismologist Jian Lin and geophysicists Mark Behn and Laurent Montesi, all from the WHOI Department of Geology and Geophysics. Their findings were published in the July 12 issue of the journal Nature.



Oceanic transform faults cut across the mid-ocean ridge system, the 40,000-mile-long mountainous seam in Earth’s crust that marks the edges of the planet’s tectonic plates. Along some plate boundaries, such as the Mid-Atlantic Ridge, new crust is formed. In other regions, such as the western Pacific, old crust is driven back down into the Earth.



If you imagine the mid-ocean ridge as the seams on a baseball, then transform faults are the red stitches, lying mostly perpendicular to the ridge. These faults help accommodate the motion and geometry of Earth’s tectonic plates, cracking at the edges as the different pieces of rocky crust slip past each other.



The largest earthquakes at mid-ocean ridges tend to occur at transform faults. Yet while studying seafloor faults along the fast-spreading East Pacific Rise, Gregg and colleagues found that earthquakes were not as large in magnitude or resonating as much energy as they ought to, given the length of these faults.



The researchers decided to examine gravity data collected over three decades by ships and satellites, along with bathymetry maps of the seafloor. Conventional wisdom has held that transform faults should contain rocks that are colder, denser, and heavier than the new crust being formed at the mid-ocean ridge. Such colder and more brittle rocks should have a “positive gravity anomaly”; that is, the faults should exert a stronger gravitational pull than surrounding seafloor region. By contrast, the mid-ocean ridge should have a lesser gravity field, because the crust (which is lighter than underlying mantle rocks) is thicker along the ridge and the newer, molten rock is less dense.


But when Gregg examined gravity measurements from the East Pacific Rise and other fast-slipping transform faults, she was surprised to find that the faults were not exerting extra gravitational pull. On the contrary, many seemed to have lighter rock within and beneath the faults.



“A lot of the classic characteristics of transform faults didn’t make sense in light of what we were seeing,” said Gregg. “What we found was the complete opposite of the predictions.”



The researchers believe that many of the transform fault lines on the ocean floor are not as continuous as they first appear from low-resolution maps. Instead these fault lines are fragmented into smaller pieces. Such fragmented structure makes the length of any given earthquake rupture on the seafloor shorter—giving the earthquake less distance to travel along the surface.



It is also possible that magma, or molten rock, from inside the earth is rising up beneath the faults. Earthquakes stem from the buildup of friction between brittle rock in Earth’s plates and faults. Hot rock is more ductile and malleable, dampening the strains and jolts as the crust rubs together and serving as a sort of geological lubricant.



“What we learn about these faults and earthquakes underwater could help us understand land-based faults such as the San Andreas in California or the Great Rift in eastern Africa,” said Lin, a WHOI senior scientist and expert on seafloor earthquakes. “In areas where you have strike-slip faults, you might have smaller earthquakes when there is more magma and warmer, softer rock under the fault area.”



The findings by Gregg, Lin, and colleagues may also have implications for understanding the theory of plate tectonics, which says that new crust is only formed at mid-ocean ridges. By traditional definitions, no crust can be created or destroyed at a transform fault. The new study raises the possibility that new crust may be forming along these faults and fractures at fast-spreading ridges such as the East Pacific Rise.



“Our understanding of how transform faults behave must be reevaluated,” said Gregg. “There is a discrepancy that needs to be addressed.”



Funding for this research was provided by the NSF Graduate Research Fellowship Program, the WHOI Deep Ocean Exploration Institute, the NSF Ocean Sciences Directorate, and the Andrew W. Mellon Foundation Awards for Innovative Research.