Earthquake Focal Mechanisms from the New Madrid Seismic Zone

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Earthquake Focal Mechanisms from the New Madrid
Seismic Zone Thesis Proposal Brown Bag Greg
Johnson
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• Outline
• 1) Purpose
• 2) Study area
• 3) Data Method
• 4) Preliminary Results
• 5) Future Work

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• Purpose
• History Limited number of available focal
  mechanisms
• Herrmann Surface wave studies of larger events
• Lui Microearthquake focal mechanisms using
• waveform modeling and PANDA data
• Chiu P-wave first motion study from PANDA
• recorded events
• New three component data 2000-2007
• Better locations s-wave picks
• SH-wave polarity
• Generate a more complete catalogue of earthquake
  focal mechanisms
• Seismotectonic model

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• Data
• Pre-1995 single component data and PANDA data
• 1995-1999 New Madrid seismic network updates
• 96 three-component stations and 13 broadband
  seismometers
• 2000-2007 data set 1567 events
• md 4.0 - 4 events
• 3.0 md lt 4.0 - 13 events
• 2.0 md lt 3.0 - 284 events
• 1.0 md lt 2.0 - 1190 events
• 0 lt md lt 1.0 - 76 events

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Method - Generation of earthquake focal mechanisms
FPFIT Use only P-wave Polarity Parameter
Estimate Strike 200 15 Dip 85
28 Rake - 5 35 Constrained FM when
uncertainty 20
FOCMEC Combine SH- first motion polarity
observations Parameter Estimate Strike 180
6 Dip 40 5 Rake 90 8
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Study Area

• New Madrid Seismic Zone
• Seismicity
• Northern Mississippi embayment
• Structure
• Embayment structures
• Focal mechanisms available
• Herrmann - 16
• Lui - 54
• Chiu - 9
• Allison Shumway - ?

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Method - Mapping focal mechanisms
1) Distribution of focal mechanisms on
segments
2) Categorize type by rake
3) Characterization
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Seismic Cross Sections
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Cartoon
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Preliminary Results Central segment 28 of
focal mechanisms identified with this segment
show reverse slip on a nodal plane striking
N21W with 45º dip to the southwest
Totals Reverse slip 50 Strike slip
21 Normal slip 29 Southern segment 19
of the focal mechanisms identified with this
segment show right-lateral strike-slip on a
nearly vertical nodal plane striking N50E
Totals Reverse slip 35 Strike slip
49 Normal slip 16 Northern segment 45
of the focal mechanisms identified with this
segment show right-lateral strike-slip on a
nearly vertical nodal plane striking N30E
Totals Reverse slip 41 Strike slip
55 Normal slip 4
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Future work Complete 2007 dataset Evaluate
and archive focal mechanisms Update catalog
and map Seismotectonic Model (time permitting)
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Thanks to my graduate committee for their help
and support throughout this study. Mitch M.
Withers Stephen P. Horton Randy T. Cox
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