earthquake focal mechanisms from the new madrid seismic zone thesis proposal brown bag greg johnson
DESCRIPTION
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 modelTRANSCRIPT
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: 2000-2007•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
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
Method - Generation of earthquake focal mechanisms
FPFIT Use only P-wave Polarity
Parameter Estimate:Strike = 200° ± 15Dip = 85° ± 28Rake = - 5° ± 35
Constrained FM when uncertainty ≤ 20°
FOCMECCombine SH- first motion polarity observations
Parameter Estimate
Strike = 180° ± 6Dip = 40° ± 5Rake = 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
• TotalsReverse 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
• TotalsReverse 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
• TotalsReverse 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