Media Advisory: Scientists Explore Quake Zone Southwest of New Madrid

Between Little Rock, Ark., and Memphis, Tenn., scientists have found evidence of an earthquake source capable of magnitude 7 or greater earthquakes located at the southwestern end of the ancient Reelfoot Rift. This is the same geologic structure that hosts the New Madrid seismic zone which is responsible for the major earthquakes that occurred in the midcontinent almost 200 years ago.

The geologic proof includes large, visible sand blows formed by strong ground shaking, and subsurface geophysical imaging of faulting nearby. Field observations and radiocarbon dating suggest that the sand blows formed as the result of two to four earthquakes between 4,800 and 10,000 years ago.

As part of the Eastern Section of the Seismological Society of America meeting in Little Rock, Oct. 17-18, scientists from around the world will examine this evidence of the prehistoric earthquakes exposed in a trench that was excavated across one of the prominent sand blows. Geological techniques used to map sand blows, feeder dikes, and related ground failure to characterize faulting will also be shared.

When:	Sunday, Oct. 16, 12 p.m.
Who:	Scientists from the U.S. Geological Survey, University of Arkansas at Little Rock, and other earthquake experts from around the world.
Where:	Lee Road 232, Marianna, Ark., GPS coordinates 34.705229,-90.801787: a site of large and weathered sand blows that formed between 4.8 and 10 thousand years ago in the Marianna area. The site is approximately 1.5 hours from Memphis and 2 from Little Rock. Please contact Heidi Koontz at hkoontz@usgs.gov for exact directions.
Why:	Major earthquakes have occurred in the New Madrid area for centuries. Scientists are studying geologic and geophysical clues to better understand what has occurred prior to the historic record of earthquakes in order to better understand what is likely to occur in the future.

Click here for more information about the New Madrid Earthquake Bicentennial.

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Parameter	Value	Description
Magnitude	mb	The magnitude for the event.
Longitude	° East	Decimal degrees longitude. Negative values for western longitudes.
Latitude	° North	Decimal degrees latitude. Negative values for southern latitudes.
Depth	km	Depth of the event in kilometers.
Place		Textual description of named geographic region near to the event. This may be a city name, or a Flinn-Engdahl Region name.
Time	1970-01-01 00:00:00	Time when the event occurred. UTC/GMT
Updated	1970-01-01 00:00:00	Time when the event was most recently updated. UTC/GMT
Timezone offset		Timezone offset from UTC in minutes at the event epicenter.
Felt		The total number of felt reports
CDI		The maximum reported intensity for the event.
MMI		The maximum estimated instrumental intensity for the event.
Alert Level		The alert level from the PAGER earthquake impact scale. Green, Yellow, Orange or Red.
Review Status		Indicates whether the event has been reviewed by a human.
Tsunami		This flag is set to "1" for large events in oceanic regions and "0" otherwise. The existence or value of this flag does not indicate if a tsunami actually did or will exist.
SIG		A number describing how significant the event is. Larger numbers indicate a more significant event.
Network		The ID of a data contributor. Identifies the network considered to be the preferred source of information for this event.
Sources		A comma-separated list of network contributors.
Number of Stations Used		The total number of Number of seismic stations which reported P- and S-arrival times for this earthquake.
Horizontal Distance		Horizontal distance from the epicenter to the nearest station (in degrees).
Root Mean Square	sec	The root-mean-square (RMS) travel time residual, in sec, using all weights.
Azimuthal Gap		The largest azimuthal gap between azimuthally adjacent stations (in degrees).
Magnitude Type		The method or algorithm used to calculate the preferred magnitude for the event.
Event Type		Type of seismic event.
Event ID		Id of event.
Event Code		An identifying code assigned by, and unique from, the corresponding source for the event.
Event IDS		A comma-separated list of event ids that are associated to an event.

Parameter

Value

Description

Magnitude

The magnitude for the event.

Longitude

° East

Decimal degrees longitude. Negative values for western longitudes.

Latitude

° North

Decimal degrees latitude. Negative values for southern latitudes.

Depth

Depth of the event in kilometers.

Place

Textual description of named geographic region near to the event. This may be a city name, or a Flinn-Engdahl Region name.

Time

1970-01-01 00:00:00

Time when the event occurred. UTC/GMT

Updated

1970-01-01 00:00:00

Time when the event was most recently updated. UTC/GMT

Timezone offset

Timezone offset from UTC in minutes at the event epicenter.

Felt

The total number of felt reports

CDI

The maximum reported intensity for the event.

MMI

The maximum estimated instrumental intensity for the event.

Alert Level

The alert level from the PAGER earthquake impact scale. Green, Yellow, Orange or Red.

Review Status

Indicates whether the event has been reviewed by a human.

Tsunami

This flag is set to "1" for large events in oceanic regions and "0" otherwise. The existence or value of this flag does not indicate if a tsunami actually did or will exist.

SIG

A number describing how significant the event is. Larger numbers indicate a more significant event.

Network

The ID of a data contributor. Identifies the network considered to be the preferred source of information for this event.

Sources

A comma-separated list of network contributors.

Number of Stations Used

The total number of Number of seismic stations which reported P- and S-arrival times for this earthquake.

Horizontal Distance

Horizontal distance from the epicenter to the nearest station (in degrees).

Root Mean Square

sec

The root-mean-square (RMS) travel time residual, in sec, using all weights.

Azimuthal Gap

The largest azimuthal gap between azimuthally adjacent stations (in degrees).

Magnitude Type

The method or algorithm used to calculate the preferred magnitude for the event.

Event Type

Type of seismic event.

Event ID

Id of event.

Event Code

An identifying code assigned by, and unique from, the corresponding source for the event.

Event IDS

A comma-separated list of event ids that are associated to an event.

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Media Advisory: Scientists Explore Quake Zone Southwest of New Madrid

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