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

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Presentation transcript:

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 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: Better locations – s-wave picks SH-wave polarity Generate a more complete catalogue of earthquake focal mechanisms Seismotectonic model

Data Pre-1995: single component data and PANDA data : New Madrid seismic network updates 96 three-component stations and 13 broadband seismometers data set: 1567 events m d ≥ events 3.0 ≤ m d < events 2.0 ≤ m d < events 1.0 ≤ m d < events 0 < m d < events

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

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

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

Seismic Cross Sections

Cartoon

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%

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

Thanks to my graduate committee for their help and support throughout this study. Mitch M. Withers Stephen P. Horton Randy T. Cox