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detectible Present Earthquakes by decade


									Inspection and Analysis of
Patterns and Anomalies in
Earthquake Data From the New
Madrid Fault
Trina Merrick
GSC 521
November 19, 2009

Project Goals
 Detect patterns by date, location, and
  magnitude of earthquakes in the New
  Madrid Fault Zone
 Look for increase in or diminishing
  activity, intensity, changes in depth
 Inquiry on shifting of epicenter locations
 Provide a Basis for Future Research on
  the Fault Area

 This research used New Madrid area
  earthquake data collected from 1974
  to present.
 GIS (ArcMap) was used to process,
  analyze and display the data in order
  to look for specific geologic trends.

Background: The New Madrid Fault

 Scientific Basics
 History
 Data Collection

The Scientific Basics: New Madrid
   The system is a series of faults buried deep
    beneath the crust that runs 150 miles involving
    eight states and crossing the Mississippi River in
    three places or more.
   The weak area is known as the Reelfoot Rift. The
    zone is unlike the Western Faults, which lie on a
    Plate Boundary. Instead, a weak area in the crust
    which is probably put under stress due to the
    North American Plate pushing against the Pacific
    Plate. The release of the stress on the rocks
    occurs during an earthquake.   5
A Brief History of New Madrid
Seismic Zone
In ancient times, a rift began to form in the North American Plate, but did not
    penetrate the surface. The reasons are unclear, but glacial weight,
    geology, and hydrology could have all played roles. The thin portion filled
    with upwelling igneous rock, which differed from its surroundings.
Probable stress from forces on the North American Plate by other plates
    caused earthquakes, even in ancient times, as evidenced by sand blows
    and geology uncovered by scientists studying paleosiesmology of the
The largest Earthquakes in the continental US East of the Rocky Mountains
    occurred in the New Madrid Fault Zone Area in the 1800’s.
Between 1811 and 1812, 4 earthquakes magnitude estimated at greater than
    7.0, occurred over 3months. Aftershocks were common for many years.
January 4, 1843 saw an earthquake of an estimated 6.0 and on October 31, an
    earthquake of estimated 6.2 magnitude occurred.
In 1974 Instruments were installed in and around the area.
As of November 2, 2009 Approximately 6653 earthquakes have been detected
    by the instruments.

A Brief History of New Madrid
Seismic Zone Data
 Data was collected on earthquakes prior
  to 1974 by interviewing and researching
  historical accounts, rather than by
  technical means.
 Since 1974, a catalog of Seismic Data has
  been kept and has been utilized for this
 Magnetic Field, Gravitational Field Data,
  and many other types of data are being
  collected on a larger scale than ever
  before around the globe.
Different than other Faults
   While data is available on the earthquakes
    in the region (both recent and historical),
    there is less clearly known about the
    specific nature of the New Madrid Fault
    Zone (and nearby active areas).
    The reasons are varied, but stem largely
    from the fact that it is an intraplate seismic
    zone and does not have many features on
    the surface.
Intraplate Earthquakes
   Less than 10 % of all Earthquakes on Earth are
    intraplate, yet 2/3 of the Earth’s Crust is stable
    interior crust
   Many are weakened former plate boundaries or
    areas where the crust was not completely
    penetrated by a rift
   Less understood than plate boundary quakes
   Longer recurrence time than boundary quakes
   Release more force per unit area than boundary
   Many times are in areas of ancient divergence
   The study of
    earthquakes in the
    New Madrid
    Seismic Zone
    sheds some light
    on the activity in
    the region

                 Chart courtesy of:
Message from Center for Earthquake
Research and Information (CERI)
When you visit the CERI site and try to pull up a map of the fault lines:

Known hazardous faults and fault zones shown on maps
“The Central and Southeast U.S. region covers a large area of relatively
   diffuse, low rate seismicity. Principal areas of activity include the New
   Madrid Seismic Zone, the East Tennessee, and Southern Appalachian
   Seismic Zones, and South Carolina. Earthquakes do occur throughout the
   entire region. Due to the relatively low rate of seismicity, ground cover,
   deep soil, etc, most faults within the region aren't even mapped. Even the
   precise location of faults within the New Madrid Seismic Zone are subject
   to debate (though it is becoming more clear). Thus, unlike other recent eqs
   systems, we have elected not to show faults. “

Map of Other Faults vs. Map of New

San Bernardino, CA Area   Mississippi River
                          Valley Area
Basic Statistics
 Total Earthquakes (all detectible) 1974-Present:
 Earthquakes by decade:
1970s 1125
1980s 2361
1990s 969
2000s 2198
The difference in number could be attributed to
  fluctuations in numbers, but could also be due to
  sensing equipment improvement, new
  installations, and improved sensitivity and
  reporting techniques.
Earthquakes by Decade: 1970s

Earthquakes by Decade: 1980s

Earthquakes by Decade: 1990s

Earthquakes by Decade: 2000s

Earthquakes by Decade: Analysis
 A visual comparison of the Earthquake
  Maps did not reveal any significant
  patterns by location, date, or magnitude
 Several problems with data analysis were
  clear: Date ranges for each decade were
  uneven, seismic sensors varied in number
  over the decades, and seismic sensitivity
  varied over the time span.
 Statistical analysis was needed.
Directional Distribution by Decade

Directional Distribution Statistics
   A Directional Distribution of one
    Standard Deviation was run on each
    decade of data to look for trends or
    changes in patterns of earthquakes.

Overlay of Directional Distribution

Directional Distribution Overlay
   There was some change in
    distribution over the decades,
    however, it was not in a consistent
    direction. The larger distribution of
    later earthquakes could be attributed
    to more data points due to greater
    sensitivity of equipment and a
    greater number of small earthquakes
    in the mid-Tennessee area.
Mean Center
By Decade

This analysis, again
did not reveal any
significant pattern to
aid in further
understanding of the
nature of the fault

Analysis of Significant Earthquakes (Richter Scale)

  No Significant findings
  came from running this
  filter, however, this
  does show that the
  NMSZ, does in fact
  have less frequent
  4.0plus events than
  most interplate fault

Analysis and Observations by Depth

No significant patterns were discernable by depth.   25
Future Research and Extensions
    There are many research questions related to this study. Some interesting extensions
     might be:
Would extensive magnetic field and gravitational field data reveal significant patterns that
     would lead to better mapping and/or preparedness models of the New Madrid Seismic
Would depth analysis for data collected by seismic sensors provide a basis for better
     mapping and/or preparedness models of the New Madrid Seismic Zone?
Would Magnetic Field, Gravitational Field sensing and GPS data support or refute the
     hypothesis/theory of diminishing threat of the New Madrid Seismic Zone?
Would hydrological analysis and geologic chemistry provide insight into patterns of
     intensity and occurrence of intraplate earthquakes?
If the New Madrid Seismic Zone is “dying”, would analysis of geophysical features, such
     as deep igneous structures, predict the next intraplate seismic zone affected?

   In order to truly predict the future of the NMSZ, a more complete analysis is
    necessary. This must include a 3D approach, rather than a conventional 2D surface
    analysis that has been used thus far. While 2D surface analysis may be sufficient for
    plate boundary seismic zones, the intraplate zones do not have surficial components,
    and cannot be completely understood in this manner. A 3D study might include any
    combination of depth analysis of epicenters, hydrology and geology, magnetic data,
    gravitational data, GPR, GPS, and other sources.

Personal Achievements
   Although the statistical analysis of the data was
    simplistic and, in most contexts, uneventful and
    unoriginal (many of the references I included
    have completed much more sophisticated
    analysis on the same data), the majority of time
    spent was in research of the seismic zone and
    applying skills in GIS. This powerful program and
    the complex nature of the seismic zone will
    continue to provide researchers with a wealth of
    questions to explore far into the future.

     Kaye M. Shedlock, "Intraplate earthquakes", in AccessScience@McGrawHill,, DOI 10.1036/10978542.YB010921
     USGS Earthquakes:maps
     USGS Earthquakes:maps
      Data for Quaternary faults, liquefaction features, and possible tectonic features in the Central and
      Eastern United States, east of the Rocky Mountain front; U.S. Department of the Interior, U.S.
      Geological Survey; By Anthony J. Crone and Russell L. Wheeler; Open-File Report 00-260; 2000 USGS
Data for Quaternary faults, liquefaction features, and possible tectonic features in the Central and
      Eastern United States, east of the Rocky Mountain front; U.S. Department of the Interior, U.S.
      Geological Survey; By Anthony J. Crone and Russell L. Wheeler; Open-File Report 00-260; 2000 USGS

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