Title: Finding NMEO New Madrid Earth Observatory Targets, Approaches, Problems
1Finding NMEO - New Madrid Earth
ObservatoryTargets, Approaches, Problems
- Chuck Langston
- CERI
- University of Memphis
- May 3, 2007
2Where to?
- Intraplate Earthquake Sources
- Wave Propagation in the Continental Interior
- Geological Structure
3Intraplate Earthquake Sources
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55 Sequences of Events over 2400 years
Tuttle, Schweig, Sims, Lafferty, Wolf, and Haynes
(2002)
6 7Miao (2007)
8Miao (2007)
9GPS
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
10 11Forte et al (2007)
12Fundamental Scientific Problem of Intraplate
Earthquakes
- Apparent Low Strain Rate over Geological Time
- Paleoseismic Evidence of 3, possibly 5, Clusters
of Large Events - Continuing Seismicity
13Unusual Geological Setting
14Unconsolidated 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
15- Jemberie and Langston (2005)
16Mississippi Embayment
17Typical Cross Section
18Target 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
19Approach
- PBO Strain Instrument and Sensitive Broad Band
Sensor Beneath Unconsolidated Sediments - Blytheville Deep Earthquake Cluster
- Reelfoot Fault
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21Problems
- Drilling into limestone karst _at_ 800 - 1000m
- Emplacement of a deep strainmeter
- Will it be deep enough to avoid significant
structure effects?
22The top 5 km
Installation
23Target Intraplate Earthquake Source
- Determine Physical Properties of the active
Reelfoot Fault - Pore pressure
- Rock fabric
- Geometry
- Monitor Fault Strain
24Approach
- ReelFOD
- Drill the fault in the Paleozoic Section (1km)
25Problems
- Drilling into Karst
- Finding the Reelfoot Fault
- Possibly not a seismogenic or creeping part of
the fault
26Seismic 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.?
27Target 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?
28Approach Vertical Accelerometer Array
- Central United States Seismic Observatory - U of
Kentucky
U of Kentucky website
29Chavarria, Malin, and Shalev (2004)
30Problems
- Will be a main topic of discussion at the workshop
31Target 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
32Approach 1 to 3 Surface Seismic Arrays
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34Problems
Attributes
- Integration within existing facility
- Regional observatory as well as local
35Geological Structure
- What is the geological structure beneath the
unconsolidated sediments? - What is its history?
- How is it related to current tectonics?
36Target 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?
37Mid-America
Canadian shield
Rocky Mountains
Great Plains
Interior basins and domes
Appalachians
Gulf Coastal Plain
Bill Thomas
38Juanjuan Cao
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41Latest 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
42How old is the Reelfoot Fault?
Ivan Rabak
43- Pascola Arch
- Dart (1998)
- Antiform showing 2 km of erosion
- At least since Cretaceous
44- Magnetic Anomaly
- Basin Depth
- Paleozoic subcrop
45Approach Data Depository
- Available seismic refraction data
- Available seismic reflection data
- Available potential fields data
- Available Borehole logs
- Purchase addition existing reflection data
46Problems
- Data Mining - much exists
- Costs of industry data
- Archiving method
47NMEO?
Surface Array Deep PBO BB ReelFOD
PBO CUSSO Data Depository Additional GPS
48NMEO?
- What is possible?
- What will give the most scientific and
engineering value? - What will NMEO be?
- How do we do it?
- Who is interested?