* Astronomy

Date: Jan 19 04:27 2010

RE: Earthquake

Blobrana · L

Measuring the magnitude of earthquakes

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Earthquake Magnitude Scale

Magnitude	Earthquake Effects	Estimated Number Each Year
2.5 or less	Usually not felt, but can be recorded by seismograph.	900,000
2.5 to 5.4	Often felt, but only causes minor damage.	30,000
5.5 to 6.0	Slight damage to buildings and other structures.	500
6.1 to 6.9	May cause a lot of damage in very populated areas.	100
7.0 to 7.9	Major earthquake. Serious damage.	20
8.0 or greater	Great earthquake. Can totally destroy communities near the epicenter.	One every 5 to 10 years

Earthquake Magnitude Classes

Earthquakes are also classified in categories ranging from minor to great, depending on their magnitude.

Class	Magnitude
Great	8 or more
Major	7 - 7.9
Strong	6 - 6.9
Moderate	5 - 5.9
Light	4 - 4.9
Minor	3 -3.9

The Richter magnitude scale, also known as the local magnitude (ML) scale, assigns a single number to quantify the amount of seismic energy released by an earthquake. It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitude of the largest displacement from zero on a WoodAnderson torsion seismometer output. So, for example, an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0. The effective limit of measurement for local magnitude ML is about 6.8.
Source

Blobrana · L

Geologic faults

Blobrana · L

RE: Earthquake

Blobrana · L

The CISN ShakeAlert system

An earthquake early warning system for California is feasible in coming years, according to research being presented Dec. 14-15 at the American Geophysical Union meeting in San Francisco. The ongoing study demonstrates that an earthquake early warning system for California is possible and lays out how such a system could be built.
Earthquake early warning systems, already successfully deployed in Mexico, Japan and Taiwan, can detect an earthquake in progress and provide notice of seconds to tens of seconds prior to actual ground shaking. Building on developments in other countries with significant earthquake risk, scientists are exploring early warning in the United States.
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Blobrana · L

U.S. seismologists have found evidence that the massive 2004 earthquake that triggered killer tsunamis throughout the Indian Ocean weakened at least a portion of California's famed San Andreas Fault. The results, which appear this week in the journal Nature, suggest that the Earth's largest earthquakes can weaken fault zones worldwide and may trigger periods of increased global seismic activity.

"An unusually high number of magnitude 8 earthquakes occurred worldwide in 2005 and 2006. There has been speculation that these were somehow triggered by the Sumatran-Andaman earthquake that occurred on Dec. 26, 2004, but this is the first direct evidence that the quake could change fault strength of a fault remotely" - study co-author Fenglin Niu, associate professor of Earth science at Rice University.

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The only link between deadly earthquakes in Indonesia and the South Pacific was the stretch of seismic activity where they struck - the site of most of the world's quakes, according to experts.
They said that Tuesday's 8.0-magnitude quake that hit the remote Pacific islands of Samoa and Western Samoa and a 7.6 tremor the next day in Indonesia were along the "Ring of Fire" on the Australian tectonic plate, but too far apart for any connection.

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Blobrana · L

Distant earthquakes may increase the risk of subsequent earthquakes around the globe, a team of US seismologists reports.
Examining 22 years of seismic data from a section of the San Andreas fault near the small central Californian town of Parkfield - an earthquake hotspot - the researchers found a substantial upsurge in the frequency of small earthquakes in 2005. These occurred following the SumatraAndaman earthquake in late 2004, which caused the deadly Indian Ocean tsunami.

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Blobrana · L

U.S. researchers try to use Twitter in reporting quakes
U.S. researchers are studying the possibility of using Twitter to report earthquakes, a U.S. Geological Survey scientist said Saturday. Scientists have begun using a Twitter pipeline to monitor use of words quake, earthquake and terremoto -- the Spanish word for earthquake -- on the Web.

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Blobrana · L

Author William K. Vogeler Says Gravity Wobble Caused Big Earthquakes

Author of An Amateur Astronomer's Guide to Gravity to Speak at Pacific Astronomy and Telescope Show
Many of the largest earthquakes in history may have been caused by a wobble in the Earth's obit, according to an author of a new book about gravity.
William K. Vogeler, speaking to astronomers at the Pasadena Convention Centre this month, will explain how recent gravity measurements support his theory. Vogeler contends that the Earth shudders as it approaches the Sun.

Source

Ed ~ This is an unusual claim, that somehow seems to goes against preceding research that shows there is no correlation, or pattern, to large earthquakes.

Blobrana · L

Typhoons trigger slow earthquakes
Scientists have made the surprising finding that typhoons trigger slow earthquakes, at least in eastern Taiwan. Slow earthquakes are non-violent fault slippage events that take hours or days instead of a few brutal seconds to minutes to release their potent energy. The researchers discuss their data in a study published in the June 11, issue of Nature.

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