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The Sound Of A Distant Rumble: Researchers Track Underwater Noise Generated By December 26 Earthquake

Date:
July 23, 2005
Source:
The Earth Institute at Columbia University
Summary:
Underwater sound picked up by the network that monitors the globe for nuclear test explosions, enabled researchers to analyze the rupture as it progressed along the Sumatra Fault on December 26. The study found that the earthquake may have occurred in two distinct phases and points to the need for scientists and disaster response officials to have access to the monitoring data in real time.

Time After Event Origin Time (seconds).
Credit: Image courtesy of The Earth Institute at Columbia University

When the sea floor off the coast of Sumatra split on the morning of December 26, 2004, it took days to measure the full extent of the rupture. Recently, researchers at Columbia University's Lamont-Doherty Earth Observatory analyzed recordings of the underwater sound produced by the magnitude 9.3 earthquake. Their unique approach enabled them to track the rupture as it moved along the Sumatra-Andaman Fault, raising the possibility that scientists could one day use the method to track underwater earthquakes in near real time and opening new avenues in seismologic research.

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"We were able to constrain some details such as the speed and duration of the rupture more accurately than traditional seismic methods," said Maya Tolstoy, a Doherty Research Scientist and lead author of the study. "Moreover, we found the earthquake happened in two distinct phases, with faster rupture to the south and slower to the north, almost as if there were two back-to-back events." The study appears in the July/August edition of Seismological Research Letters.

The researchers found that the first phase encompassed the first three minutes of the eight-minute earthquake, during which the rupture proceeded north at about 1.7 miles per second (2.8 km/sec) from the epicenter. During the second phase, the rupture slowed to 1.3 miles per second (2.1 km/sec) and continued north for another five minutes until it reached a plate boundary where the fault changes from subduction to strike-slip. This suggests that had the subduction zone continued, this longest-ever-recorded earthquake might have been even longer.

The analysis that Tolstoy and her co-author DelWayne Bohnenstiehl used also shows promise for helping officials quickly determine where relief activities are needed. In the case of the Indonesian earthquake, early seismic data indicated that only the southernmost third of the fault was involved. Later analysis revealed that about 750 miles actually ruptured, a finding that was supported by Tolstoy and Bohnenstiehl’s study.

Recently the International Monitoring System of the Comprehensive Nuclear Test Ban Treaty, which operates the microphones that picked up sounds of the earthquake, began making their data available on a trial basis to tsunami warning organizations recognized by UNESCO. Tolstoy hopes that eventually scientists will gain easier access to these data as well, which would help them learn more about the basic processes of the Earth. "There is an opportunity here to make a contribution to international disaster monitoring, as well as help us better understand earthquakes and tsunamis and potentially mitigate these events in the future." said Tolstoy. "It makes sense to let others listen in."

About The Lamont-Doherty Earth Observatory
The Lamont-Doherty Earth Observatory, a member of The Earth Institute at Columbia University, is one of the world's leading research centers seeking fundamental knowledge about the origin, evolution and future of the natural world. More than 200 research scientists study the planet from its deepest interior to the outer reaches of its atmosphere, on every continent and in every ocean. From global climate change to earthquakes, volcanoes, nonrenewable resources, environmental hazards and beyond, Observatory scientists provide a rational basis for the difficult choices facing humankind in the planet's stewardship. For more information, visit www.ldeo.columbia.edu.

About The Earth Institute at Columbia University
The Earth Institute at Columbia University is the world’s leading academic center for the integrated study of Earth, its environment and society. The Earth Institute builds upon excellence in the core disciplines—earth sciences, biological sciences, engineering sciences, social sciences and health sciences—and stresses cross-disciplinary approaches to complex problems. Through research, training and global partnerships, the Earth Institute mobilizes science and technology to advance sustainable development, while placing special emphasis on the needs of the world’s poor.



Story Source:

The above story is based on materials provided by The Earth Institute at Columbia University. Note: Materials may be edited for content and length.


Cite This Page:

The Earth Institute at Columbia University. "The Sound Of A Distant Rumble: Researchers Track Underwater Noise Generated By December 26 Earthquake." ScienceDaily. ScienceDaily, 23 July 2005. <www.sciencedaily.com/releases/2005/07/050722132947.htm>.
The Earth Institute at Columbia University. (2005, July 23). The Sound Of A Distant Rumble: Researchers Track Underwater Noise Generated By December 26 Earthquake. ScienceDaily. Retrieved December 18, 2014 from www.sciencedaily.com/releases/2005/07/050722132947.htm
The Earth Institute at Columbia University. "The Sound Of A Distant Rumble: Researchers Track Underwater Noise Generated By December 26 Earthquake." ScienceDaily. www.sciencedaily.com/releases/2005/07/050722132947.htm (accessed December 18, 2014).

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