FLO-LOC's FLO-NOTES

Providing general information of interest regarding FLO-LOC's products & services,
and earthquake-related terminology, articles, photos, & web links.

Why does FLO-LOC calibrate its seismic sensor in "percent of g"?

The evening news usually reports the strength of an earthquake as an number on the "Richter Scale". This is not a precise measure of the severity of an earthquake. That numerical scale of magnitude, devised by C.F. Richter in 1935, which describes the magnitude or the amount of energy released by an earthquake at its source is now rarely used by the scientific community. Instead there are several other methods of calculating magnitude, all of which give different numbers for the same seismic event. Then there is the "Modified Mercalli Scale" which measures, subjectively, the effects of a seismic event at a particular distance from its epicenter, giving us yet another number. Because of all this confusion of numbers, the news media usually takes the largest available number and report it as "Richter".*

The severity of an earthquake at any particular place is called "intensity" and is calculated from the amount of ground motion measured there. The intensity of an earthquake at your location is affected by many factors including the distance from the earthquake's epicenter and the nature of the underlying rock and soil.

Currently there are no national standards in place for seismic shutoff devices in the water industry, therefore FLO-LOC, Inc. adheres to those requirements set by the State of California for its approval of seismic shutoff devices for gas valves. The method used by the State of California is to measure ground displacement at a particular location as a percent of g. or gravity. A force equal to one g. will cancel gravity and make any mass weightless. Although this is rarely encountered, the Landers California earthquake of June 28, 1992 produced a ground displacement of at least one g. as their three million gallon reservoir, located unfortunately at the earthquake's exact epicenter, was lifted approximately one meter off the ground, then dropped, splitting its seams and instantly dumping its water.

FLO-LOC typically sets its seismic sensors at .25g., the point just before which damage to valves and distribution systems may occur. The exact setting for any FLO-LOC seismic sensor will of course depend upon the nature of the underlying rock and soil at your particular site.

* Source: "Damages and Losses From Future New Madrid Earthquakes." David Stewart, Associate Professor, Department of Earth Sciences, Center for Earthquake Studies, Southeast Missouri State University, August 1991.

Earthquake Terminology

Whenever an earthquake is reported on TV or in the press, one is inundated with technical terms: Richter Scale, Intensity, Magnitude, etc. We feel that a few simple definitions might help clear up these muddied waters. Here's an index, and the glossary is below.

	A - Q		R - Z

	Accelerations...		Richter Scale
	Earthquakes		Seismic Waves
	Epicenter		SCADA
	FEMA		Seismogram
	Focus		Seismograph
	Frequency		USGS
	Intensity		Waves, Body or Surface
	Liquefaction		- see Seismic Waves
	Magnitude

Glossary:

Accelerations:

Accelerations due to gravity - the vertical acceleration with which a ball falls if released at rest in a vacuum (to eliminate wind resistance). Value = 1.0g. Horizontal acceleration due to earthquakes is often expressed as a percent of gravity or %g. For example if a body weighs 100 pounds and receives a lateral earthquake force of 20 pounds, that can be expressed as a force of 20%g. (0.2g.). A vertical earthquake force in excess of 100%g. (1.0g.) will throw any object regardless of size or mass into the air. (See Landers Earthquake photos .)

Peak horizontal acceleration - maximum measurement of horizontal ground motion produced by earthquakes; stated as a percent of gravity (1.0g.).

Earthquakes:

Earthquake mitigation - planning, legislation, education and activities accomplished before an earthquake which will lessen damages to life and property during and after a seismic event. (This is one area where FLO-LOC's products can help! )

	*Any Earthquake of magnitude -*	*Earthquake rating / name -*
	2.9 or less	Very minor earthquake
	3.0 - 3.9	Minor earthquake
	4.0 - 4.9	Light earthquake
	5.0 - 5.9	Moderate earthquake
	6.0 - 6.9	Strong earthquake
	7.0 - 7.9	Major earthquake
	8.0 or greater	Great earthquake

Epicenter - the point on the surface of the earth directly above the focus of an earthquake.

FEMA - Federal Emergency Management Agency. The Federal Agency with lead responsibility for implementing the National Earthquakes Hazards Reduction Program (NEHRP), including planning, coordination, assistance to state and local programs, public education and coordination of federal response to catastrophic earthquakes.

Focus - the point within the earth's crust from which earthquake waves first originate.

Frequency - the number of waves that pass a fixed point each second. The most damaging frequencies of seismic wave range from two (2) cycles per second to as slow as one (1) cycle in three or four seconds.

Intensity (of earthquakes) - a measure of the effects of an earthquake at a particular place. Intensity depends no only on the earthquake's magnitude but also on the distance from the epicenter and on the local geology. Intensities tend to be greatest in areas underlain by wet sand or clay. See also "Earthquakes".

Liquefaction - the sudden transformation of soil into a fluid. Repeated earthquake vibrations can cause a loose, water-saturated sand to suddenly lose all of its shear strength or internal friction and collapse.

Magnitude (of earthquakes) - a measure of earthquake size, determined by taking the common logarithm (base 10) of the largest ground motion recorded during the arrival of a seismic wave type and applying a standard correction for distance to the epicenter.

Richter scale - a numerical scale of magnitude devised by C. F. Richter in 1935 which describes the quantity of energy released by an earthquake. Today, however, there are several scales used, each resulting in a different number, or magnitude, for the same event. It has become customary, in statements to the press, to quote the largest number, regardless of which scale was used, and call it "Richter".

Seismic waves - the disturbances propagated outward from the focus of an earthquake.

Body waves - seismic waves that travel through the earth. There are two kinds of body waves: P waves and S waves. The P wave, sometimes called the "primary wave" because it travels it travels faster and arrives first, is a compression wave, vibrating in the direction of propagation. The S wave, sometimes called the "secondary wave" because it arrives after the P wave, is a shear wave, vibrating at right angles to the direction of propagation.

Surface waves - seismic waves that travel only along the surface of the Earth.

SCADA - acronym for Supervisory Control And Data Acquisition.

Seismogram - the record made by a seismograph.

Seismograph - an instrument for recording as a function of time the motions of the Earth's surface that are caused by seismic waves.

USGS - United States Geological Survey. The federal agency with responsibility for determining earthquake potential, earthquake prediction, earthquake information, earthquake hazards and risk assessments and technical assistance in fostering implementation of loss-reduction measures.

(FLO-LOC's products and services assist in loss protection and secondary loss prevention; see our Products info and Installations pages!)

See Flo-Notes, page two , for photos of the Landers Earthquake of 1992.

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