Home  |  Top News  |  Most Popular  |  Video  |  Multimedia  |  News Feeds  |  Feedback
  Medicine  |  Nature & Earth  |  Biology  |  Technology & Engineering  |  Space & Planetary  |  Psychology  |  Physics & Chemistry  |  Economics  |  Archaeology
Top > Nature & Earth > Earthquake Lights Linked to Rift… >
Earthquake Lights Linked to Rift Environments, Subvertical Faults

Published: January 3, 2014.
By Seismological Society of America
http://www.seismosoc.org

SAN FRANCISCO – Rare earthquake lights are more likely to occur on or near rift environments, where subvertical faults allow stress-induced electrical currents to flow rapidly to the surface, according to a new study published in the Jan./Feb. issue of Seismological Research Letters.

From the early days of seismology, the luminous phenomena associated with some earthquakes have intrigued scholars. Earthquake lights (EQL) appear before or during earthquakes, but rarely after.

EQL take a variety of forms, including spheres of light floating through the air. Seconds before the 2009 L'Aquila, Italy earthquake struck, pedestrians saw 10-centimeter high flames of light flickering above the stone-paved Francesco Crispi Avenue in the town's historical city center. On Nov. 12, 1988, a bright purple-pink globe of light moved through the sky along the St. Lawrence River near the city of Quebec, 11 days before a powerful quake. And in 1906, about 100 km northwest of San Francisco, a couple saw streams of light running along the ground two nights preceding that region's great earthquake.

Continental rift environments now appear to be the common factor associated with EQL. In a detailed study of 65 documented EQL cases since 1600 A.D., 85 percent appeared spatially on or near rifts, and 97 percent appeared adjacent to subvertical faults (a rift, a graben, strike-slip or transform fault). Intraplate faults are associated with just 5 percent of Earth's seismic activity, but 97 percent of documented cases of earthquake lights.

"The numbers are striking and unexpected," said Robert Thériault, a geologist with the Ministère des Ressources Naturelles of Québec, who, along with colleagues, culled centuries of literature references, limiting the cases in this study to 65 of the best-documented events in the Americas and Europe.

"We don't know quite yet why more earthquake light events are related to rift environments than other types of faults," said Thériault, "but unlike other faults that may dip at a 30-35 degree angle, such as in subduction zones, subvertical faults characterize the rift environments in these cases."

Two of the 65 EQL events are associated with subduction zones, but Thériault suggests there may be an unknown subvertical fault present. "We may not know the fault distribution beneath the ground," said Thériault. "We have some idea of surface structures, but sedimentary layers or water may obscure the underlying fault structure."

While the 65 earthquakes ranged in magnitude, from M 3.6 to 9.2, 80 percent were greater than M 5.0. The EQL varied in shape and extent, though most commonly appeared as globular luminous masses, either stationary or moving, as atmospheric illuminations or as flame-like luminosities issuing from the ground.

Timing and distance to the epicenter vary widely. Most EQL are seen before and/or during an earthquake, but rarely after, suggesting to the authors that the processes responsible for EQL formation are related to a rapid build-up of stress prior to fault rupture and rapid local stress changes during the propagation of the seismic waves. Stress-activated mobile electronic charge carriers, termed positive holes, flow swiftly along stress gradients. Upon reaching the surface, they ionize air molecules and generate the observed luminosities.

Eyewitness reports and security cameras captured a large number of light flashes during the 2007 Pisco, Peru M 8.0 earthquake. Together with seismic records obtained on a local university campus, the automatic security camera records allow for an exact timing and location of light flashes that illuminated a large portion of the night sky. The light flashes identified as EQL coincided with the passage of the seismic waves.

Thériault likes the account of a local L'Aquila resident, who, after seeing flashes of light from inside his home two hours before the main shock, rushed his family outside to safety.

"It's one of the very few documented accounts of someone acting on the presence of earthquake lights," said Thériault. "Earthquake lights as a pre-earthquake phenomenon, in combination with other types of parameters that vary prior to seismic activity, may one day help forecast the approach of a major quake," said Thériault.




Translate this page: Chinese French German Italian Japanese Korean Portuguese Russian Spanish


Disclaimer: The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the ScienceNewsline.
Related »

Fault 
2/12/14 
San Francisco's Big 1906 Quake Was Third of a Series on San Andreas Fault
By University of Oregon
EUGENE, Ore. -- (Feb. 12, 2014) -- Research led by a University of Oregon doctoral student in California's Santa Cruz Mountains has uncovered geologic evidence that supports historical narratives …
Fault 
6/2/10 
BSSA Tip Sheet for June 2010 Issue
By Seismological Society of America
Revised seismotectonic model for California Central Coast – More complex than previously thought A new catalog of earthquake locations and focal mechanisms for the California Central Coast underscores …
Fault 
8/11/11 

New Data Shows El Mayor-Cucapah Earthquake Was Simple on Surface, Complicated at Depth
By California Institute of Technology
Andreas 
6/27/11 

Flooding of Ancient Salton Sea Linked to San Andreas Earthquakes
By University of California - San Diego
Lake 
2/10/11 

Lake-effect Theory Sinks, but Quake Timing Questions Go On
By University of Oregon
Earthquake 
8/1/11 
Seismology Tip Sheet from BSSA, August Issue
By Seismological Society of America
Please cite the Bulletin of the Seismological Society of America (BSSA) as the source of this information. The Table of Contents is available upon request. Limits on earthquake …
Lay 
9/20/13 
Seismologists Puzzle over Largest Deep Earthquake Ever Recorded
By University of California - Santa Cruz
A magnitude 8.3 earthquake that struck deep beneath the Sea of Okhotsk on May 24, 2013, has left seismologists struggling to explain how it happened. At a depth of …
Lay 
9/19/13 
Seismologists Puzzle over Largest Deep Earthquake Ever Recorded
By University of California - Santa Cruz
A magnitude 8.3 earthquake that struck deep beneath the Sea of Okhotsk on May 24, 2013, has left seismologists struggling to explain how it happened. At a depth of …
Fault 
9/30/10 
NOAA-sponsored Scientists First to Map Offshore San Andreas Fault And Associated Ecosystems
By NOAA Headquarters
For the first time, scientists are using advanced technology and an innovative vessel to study, image, and map the unexplored offshore Northern San Andreas Fault from north of San …
More » 

Most Popular - Nature »
ICE »
Science: There's Something Ancient in the Icebox
SPECIES »
Call for Alternative Identification Methods for Endangered Species
FOOD »
Food Shortages Could Be Most Critical World Issue by Mid-century
FOREST »
Five Anthropogenic Factors That Will Radically Alter Northern Forests in 50 Years
FIRES »
Drought And Fire in the Amazon Lead to Sharp Increases in Forest Tree Mortality
ScienceNewsline  |  About  |  Privacy Policy  |  Feedback  |  Mobile  |  Japanese
The selection and placement of stories are determined automatically by a computer program. All contents are copyright of their owners except U.S. Government works. U.S. Government works are assumed to be in the public domain unless otherwise noted. Everything else copyright ScienceNewsline.