		--- TRINET'S SHAKEMAP ---
-- A Broadcaster's Guide to Reporting Earthquake Intensity --

Earthquake Information Summary:
	Date:     	Thu Jun 11, 2009
	Time:     	01:44:55 GMT
	Location: 	N65.88 W19.74:   8.1 km SSV af Drangey
	Name:		Unnamed Earthquake (Event ID 20090611007)
	Magnitude: 	2.2


ShakeMap on the world-wide web:	  http://www.trinet.org/shake

INSTRUMENTAL INTENSITY SCALE:		 
   ESTIMATED INTENSITY		PERCEIVED SHAKING	POTENTIAL DAMAGE
   -------------------		-----------------	---------------
	I			Not Felt		None
	II-III			Weak			None
	IV			Light			None
	V			Moderate		Very Light
	VI			Strong			Light
	VII			Very Strong		Moderate
	VIII			Severe			Moderate/Heavy
	IX			Violent			Heavy
	X			Extreme			Very Heavy
   -------------------		-----------------	----------------

TRINET is the seismic network in southern California operated 
cooperatively by:
		United States Geological Survey (USGS)
  	    California Institute of Technology (Caltech)
 	   California Division of Mines and Geology (CDMG)

CONTACTS:
	Dr. David Wald, USGS, Pasadena
	Dr. Bruce Worden, USGS, Pasadena
	Mr. James Goltz, Caltech


What is earthquake intensity? How does ShakeMap display intensity?

ShakeMap is a geographic representation of the ground shaking produced by 
an earthquake. Intensity is one of the ways that ground shaking is 
expressed, along with more quantitative measures like velocity and 
acceleration. The information ShakeMap presents is different from the 
earthquake magnitude.  Magnitude is the number (for example, 7.1) that 
represents the energy released in an earthquake; a single number 
representing magnitude is assigned to each earthquake. Intensity, on the 
other hand, is a measure of how the ground shook at a particular site. So, 
while an earthquake has one magnitude and one epicenter, it produces a 
range of ground shaking levels at sites throughout the region. These 
different intensities depend on distance from the earthquake, the rock and 
soil conditions at geographical sites, and variations in the propagation 
of seismic waves from the earthquake due to complexities in the structure 
of the Earth's crust. ShakeMap focuses on the ground shaking produced by 
the earthquake, rather than the characteristics of the earthquake source.

How are earthquake intensities expressed?

Intensities portray the effects of an earthquake in a particular 
location.  These effects include potential damage, perception of shaking 
and permanent changes in topography.  Whether there was damage, and the 
severity of observed damage, is one element of intensity. Intensity scales 
also take into account how the earthquake was perceived by persons in a 
geographic location ranging from "not felt" to "unable to stand." The 
impact of the earthquake shaking on the ground, whether, for example, 
cracks or displacements occurred, or in some cases of severe shaking, 
landslides, is also a feature of measured intensity.  

The most popular intensity scale used in the United States is the Modified 
Mercalli Scale (MMI) first developed in 1931.  This scale uses Roman 
Numerals to represent progressively greater shaking from MMI I in which 
"people do not feel any earth movement" to MMI X in which "most buildings 
and their foundations are destroyed, bridges and dams are severely damaged 
and large landslides occur."  Historically, intensities were derived in 
the months following an earthquake through questionnaires sent to Post 
Offices in the impacted area.  Postal officials were asked to report the 
effects of shaking in their district and their observations were combined 
with those of scientists and engineers. When all the questionnaires and 
observations were combined, they were used to construct an intensity map 
of the earthquake.  

With the development of the new seismic network under the TriNet project, 
intensity (ShakeMaps) maps can be generated automatically from measured 
ground acceleration and velocity. These "instrumental intensities" are 
calculated and mapped within 5 minutes of the earthquake and are thus 
termed "real-time" maps.  To the extent possible, shaking expressed as 
intensity in ShakeMap correspond to the observed intensity of the older 
Modified Mercalli scale. To provide news broadcasters guidance in the 
interpretation of intensities reported in ShakeMap, we have provided below 
the ten intensity levels and the human perception, damage and topographic 
change associated with each level.

It is important to note in reporting intensity information contained in 
ShakeMap that shaking and damage vary considerably from location to 
location, and only some structures may exhibit the effects noted below in 
an area assigned a particular intensity.


MODIFIED MERCALLI INTENSITY SCALE 

MMI    
Value 		Full Description
-----	------------------------------------------------------------------------

I	People do not feel any earth movement.

II  	Felt by persons at rest, on upper floors of tall buildings 

III	Felt by people indoors.  Hanging objects swing back and forth. 
	Vibration from the earthquake may seem like the passing of light 
	trucks. May not be recognized as an earthquake.

IV      Hanging objects swing.  Vibration may seem like the passing of heavy 
	trucks or a jolt, like a heavy ball striking the walls.  Parked 
	vehicles may rock noticeably. Windows, dishes, doors may rattle and 
	glasses clink.  In the upper range of IV, walls of wood frame 
	buildings may creak.     

V	Almost everyone feels movement whether inside or outdoors. Sleeping 
	people are awakened.  Liquids in containers are disturbed; some are 
	spilled.  Small unstable objects are displaced or overturned. Doors 
	swing, close, or open.  Shutters, pictures on the wall move.       
 
VI	Felt by all; some are frightened and take cover. People have 
	difficulty walking due to motion. Objects fall from shelves and 
	dishes, glassware and ceramics may be broken. Pictures fall off 
	walls. Furniture moves or is overturned.  Weak plaster and masonry 
	cracked. Damage slight in poorly constructed buildings. Trees, bushes 
	shaken visibly or are heard rustling.

VII 	People have difficulty standing. Drivers on the road feel their cars 
	shaking. Furniture may be overturned and broken. Loose bricks fall 
	from buildings and masonry walls and cracks in plaster and masonry 
	may appear. Weak chimneys may break at the roofline. Damage is slight
	to moderate in well-built structures; considerable in poorly 
	constructed buildings and facilities.

VIII 	Drivers have trouble steering. Tall structures such as towers, 
	monuments and chimneys may twist and fall. Wood frame houses that 
	are not bolted to their foundations may shift and sustain serious 
	damage.  Damage is slight to moderate in well-constructed buildings, 
	considerable in poorly constructed buildings. Branches are broken and
	fall from trees.  Changes occur in flow or temperature of springs and 
	wells. Cracks appear in wet ground and on steep slopes. 

IX	Masonry structures and poorly constructed buildings suffer serious 
	damage or collapse. Frame structures, if not bolted, shift off 
	foundations. Serious damage to reservoirs.  Underground pipes broken.  
	Conspicuous cracks in the  ground. In alluvial areas, sand and mud 	
	ejected and sand craters are formed.

X 	Most masonry and frame structures destroyed along with their 
	foundations.  Some well-built wooden structures and bridges are 
	destroyed.  Serious damage to dams, dikes, and embankments. Large 
	landslides occur.  Water thrown on the banks of canals, rivers and 
	lakes.  Sand and mud shift horizontally on beaches and flat land.  
	Rails bent. 
-----	------------------------------------------------------------------------

Earthquake Planning Scenarios

In addition to post-earthquake shaking maps, we can estimate and display
intensities and ground motions for "Earthquake Scenarios". These are events
on faults that have ruptured in the past or have a likelihood of rupturing
in the future. The primary purpose is for emergency response exercises and
planning as well as for understanding the potential consequences of future
large earthquakes.

These earthquake scenarios are not earthquake predictions. No one knows in
advance when an earthquake will occur or how large it will be. However, if
we make assumptions about the size and location of a hypothetical
earthquake, we can make a reasonable prediction of the effects of that
earthquake, particularly the way in which the  ground will shake. This
knowledge of the potential shaking effects is the main benefit of the
earthquake scenario for planning and preparedness purposes.

Please read more about scenario earthquakes at
www.trinet.org/shake/about.html#scenario.
