Finding NMEO New Madrid Earth Observatory Targets, Approaches, Problems

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Finding NMEO - New Madrid Earth
ObservatoryTargets, Approaches, Problems

• Chuck Langston
• CERI
• University of Memphis
• May 3, 2007

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Where to?

• Intraplate Earthquake Sources
• Wave Propagation in the Continental Interior
• Geological Structure

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Intraplate Earthquake Sources
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5 Sequences of Events over 2400 years
Tuttle, Schweig, Sims, Lafferty, Wolf, and Haynes
(2002)
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• Miao (2007)

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Miao (2007)
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Miao (2007)
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GPS
11 permanent GPS stations GPS Array in Mid
America (GAMA) Velocities of GAMA sites indicate
strain rates of 10-7 per year, comparable to
those across active plate boundaries Velocities
in the far-field do not differ significantly from
zero. Smalley, Ellis, Paul, Van Arsdale(2005)
Nature 435, 1088-1090
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• Stein (2007)

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Forte et al (2007)

• Dynamic topography

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Fundamental Scientific Problem of Intraplate
Earthquakes

• Apparent Low Strain Rate over Geological Time
• Paleoseismic Evidence of 3, possibly 5, Clusters
  of Large Events
• Continuing Seismicity

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Unusual Geological Setting
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Unconsolidated Sediments of the Mississippi
Embayment

• Hides the Faults and Geology
• Separates the seismogenic region from direct
  geophysical observation
• Low impedance must be significant for shaking
  hazards assessments
• Amplifies ambient noise fields

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• Jemberie and Langston (2005)

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Mississippi Embayment
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Typical Cross Section

• Northing, degrees

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Target Intraplate Earthquake Source Processes

• Get below the unconsolidated sediments
• Low noise environment
• Avoid low Q, high wave scattering
• Source Spectra of Background Seismicity
• Microseismicity - Possible ETS (Episodic Tremor
  Source)
• Strain Transients and Dynamic Strain

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Approach

• PBO Strain Instrument and Sensitive Broad Band
  Sensor Beneath Unconsolidated Sediments
• Blytheville Deep Earthquake Cluster
• Reelfoot Fault

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Problems

• Drilling into limestone karst _at_ 800 - 1000m
• Emplacement of a deep strainmeter
• Will it be deep enough to avoid significant
  structure effects?

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The top 5 km
Installation
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Target Intraplate Earthquake Source

• Determine Physical Properties of the active
  Reelfoot Fault
• Pore pressure
• Rock fabric
• Geometry
• Monitor Fault Strain

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Approach

• ReelFOD
• Drill the fault in the Paleozoic Section (1km)

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Problems

• Drilling into Karst
• Finding the Reelfoot Fault
• Possibly not a seismogenic or creeping part of
  the fault

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Seismic Wave Propagation in the Continental
Interior

• Mississippi Embayment Sediments
• Does it really amplify seismic waves?
• Is it a potentially destructive waveguide?
• What is the nature of its non-linear, high strain
  response?
• Is distance attenuation really small in the
  Central U.S.?

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Target Sediment Amplification and Non-Linear
Response

• What is the detailed vertical velocity, density,
  and attenuation structure of the unconsolidated
  sediments?
• What is the non-linear response of the sediments?

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Approach Vertical Accelerometer Array

• Central United States Seismic Observatory - U of
  Kentucky

U of Kentucky website
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Chavarria, Malin, and Shalev (2004)

• SAFOD Pilot Hole VSP

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Problems

• Will be a main topic of discussion at the workshop

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Target Wave propagation in the sedimentary
waveguide, distance attenuation

• What are the detailed characteristics of seismic
  phases from earthquakes in an around the
  embayment?
• Amplitude decay with distance
• Horizontal slowness
• Scattering

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Approach 1 to 3 Surface Seismic Arrays

• 5 to 10 Hz

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Problems

• Siting (minor)

Attributes

• Integration within existing facility
• Regional observatory as well as local

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Geological Structure

• What is the geological structure beneath the
  unconsolidated sediments?
• What is its history?
• How is it related to current tectonics?

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Target Basement and Paleozoic Geological
Structure

• What is the configuration and geology of the
  basement?
• What are the expressions of major thermal events
  in geological history?
• What are the extent of rift structures in the
  region?
• What is the relationship of older structure on
  current faulting?

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Mid-America
Canadian shield
Rocky Mountains
Great Plains
Interior basins and domes
Appalachians
Gulf Coastal Plain
Bill Thomas
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Juanjuan Cao
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Latest Proterozoic - Early Cambrian Reelfoot
half graben no volcanism Pennsylvanian-Permia
n Appalachian Compression (Blytheville,
Pascola Arch) Thermal Event(?) igneous
activity (Fluorospar District) Triassic-Jurass
ic Gulf of Mexico Rifting, Arkansas
Transform Upper Cretaceous Thermal event -
Syenite Intrusions Uppermost Cretaceous
through Tertiary Mississippi Embayment
formation
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How old is the Reelfoot Fault?
Ivan Rabak
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• Pascola Arch
• Dart (1998)
• Antiform showing 2 km of erosion
• At least since Cretaceous

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• Magnetic Anomaly
• Basin Depth
• Paleozoic subcrop

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Approach Data Depository

• Available seismic refraction data
• Available seismic reflection data
• Available potential fields data
• Available Borehole logs
• Purchase addition existing reflection data

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Problems

• Data Mining - much exists
• Costs of industry data
• Archiving method

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NMEO?
Surface Array Deep PBO BB ReelFOD
PBO CUSSO Data Depository Additional GPS
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NMEO?

• What is possible?
• What will give the most scientific and
  engineering value?
• What will NMEO be?
• How do we do it?
• Who is interested?