Strong Earth tides can trigger earthquakes, UCLA scientists report

October 21, 2004

Earthquakes can be triggered by the Earth's tides, UCLA scientists confirmed Oct. 21 in Science Express, the online journal of Science. Earth tides are produced by the gravitational pull of the moon and the sun on the Earth, causing the ocean's waters to slosh, which in turn raise and lower stress on faults roughly twice a day. Scientists have wondered about the effects of Earth tides for more than 100 years. (The research will be published in the print version of Science in November.)

"Large tides have a significant effect in triggering earthquakes," said Elizabeth Cochran, a UCLA graduate student in Earth and space sciences and lead author of the Science paper. "The earthquakes would have happened anyway, but they can be pushed sooner or later by the stress fluctuations of the tides."

"Scientists have long suspected the tides played a role, but no one has been able to prove that for earthquakes worldwide until now," said John Vidale, UCLA professor of Earth and space sciences, interim director of UCLA's Institute of Geophysics and Planetary Physics, and co-author of the paper. "Earthquakes have shown such clear correlations in only a few special settings, such as just below the sea-floor or near volcanoes."

"There are many mysteries about how earthquakes occur, and this clears up one of them," Vidale said. "We find that it takes about the force arising from changing the sea level by a couple of meters of water to noticeably affect the rate of earthquakes. This is a concrete step in understanding what it takes to set off an earthquake."

Cochran, Vidale and co-author Sachiko Tanaka are the first researchers to factor in both the phase of the tides and the size of the tides, and are using calculations of the effects of the tides more accurate than were available just three years ago. Tanaka is a seismologist with Japan's National Research Institute for Earth Science and Disaster Prevention.

Cochran and Vidale analyzed more than 2,000 earthquakes worldwide, magnitude 5.5 and higher, which struck from 1977 to 2000. They studied earthquakes in "subduction zones" where one tectonic plate dives under another, such as near the coasts of Alaska, Japan, New Zealand and western South America. "These earthquakes show a correlation with tides because along continent edges ocean tides are strong," Vidale said, "and the orientation of the fault plane is better known than for faults elsewhere."

Cochran conducted a statistical analysis of the earthquakes and tidal stress data, using state-of-the-science tide calculations from Tanaka and the best global earthquake data, which came from Harvard seismologists. This research follows up on a 2002 study by Tanaka. The current research was funded by the National Science Foundation and the Laurence Livermore National Laboratory.

Cochran and Vidale found a strong correlation between when earthquakes strike and when tidal stress on fault planes is high, and the likelihood of these results occurring by chance is less than one in 10,000, Cochran said. They found that strong tides impose enough stress on shallow faults to trigger earthquakes. If the tides are very large, more than two meters, three?quarters of the earthquakes occur when tidal stress acts to encourage triggering, she found. Fewer earthquakes are triggered when the tides are smaller.

In California, and in fact in most places in the world, the correlation between earthquakes and tides is considerably smaller, Vidale said. In California, tides may vary the rate of earthquakes at most one or two percent; the overall effect of the tides is smaller, he said, because the faults studied are many miles inland from the coast and the tides are not particularly large.

University of California - Los Angeles

Related Stress Articles from Brightsurf:

Stress-free gel
Researchers at The University of Tokyo studied a new mechanism of gelation using colloidal particles.

Early life stress is associated with youth-onset depression for some types of stress but not others
Examining the association between eight different types of early life stress (ELS) and youth-onset depression, a study in JAACAP, published by Elsevier, reports that individuals exposed to ELS were more likely to develop a major depressive disorder (MDD) in childhood or adolescence than individuals who had not been exposed to ELS.

Red light for stress
Researchers from the Institute of Industrial Science at The University of Tokyo have created a biphasic luminescent material that changes color when exposed to mechanical stress.

How do our cells respond to stress?
Molecular biologists reverse-engineer a complex cellular structure that is associated with neurodegenerative diseases such as ALS

How stress remodels the brain
Stress restructures the brain by halting the production of crucial ion channel proteins, according to research in mice recently published in JNeurosci.

Why stress doesn't always cause depression
Rats susceptible to anhedonia, a core symptom of depression, possess more serotonin neurons after being exposed to chronic stress, but the effect can be reversed through amygdala activation, according to new research in JNeurosci.

How plants handle stress
Plants get stressed too. Drought or too much salt disrupt their physiology.

Stress in the powerhouse of the cell
University of Freiburg researchers discover a new principle -- how cells protect themselves from mitochondrial defects.

Measuring stress around cells
Tissues and organs in the human body are shaped through forces generated by cells, that push and pull, to ''sculpt'' biological structures.

Cellular stress at the movies
For the first time, biological imaging experts have used a custom fluorescence microscope and a novel antibody tagging tool to watch living cells undergoing stress.

Read More: Stress News and Stress Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to