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Earthquake Focal Mechanisms from the New Madrid Seismic Zone Thesis Proposal Brown Bag Greg Johnson

Earthquake Focal Mechanisms from the New Madrid Seismic Zone Thesis Proposal Brown Bag Greg Johnson. Outline 1) Purpose 2) Study area 3) Data & Method 4) Preliminary Results 5) Future Work. Purpose History: Limited number of available focal mechanisms

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Earthquake Focal Mechanisms from the New Madrid Seismic Zone Thesis Proposal Brown Bag Greg Johnson

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  1. Earthquake Focal Mechanisms from the New Madrid Seismic Zone Thesis Proposal Brown Bag Greg Johnson

  2. Outline 1) Purpose 2) Study area 3) Data & Method 4) Preliminary Results 5) Future Work

  3. 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

  4. 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 < 4.0 - 13 events • 2.0 ≤ md < 3.0 - 284 events • 1.0 ≤ md < 2.0 - 1190 events • 0 < md < 1.0 - 76 events

  5. 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

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

  7. Method - Mapping focal mechanisms 1) Distribution of focal mechanisms on segments 2) Categorize type by rake 3) Characterization

  8. Seismic Cross Sections

  9. Cartoon

  10. 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%

  11. Future work • Complete 2007 dataset • Evaluate and archive focal mechanisms • Update catalog and map • Seismotectonic Model (time permitting)

  12. 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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