Electronic Theses and Dissertations

Identifier

2468

Date

2015

Date of Award

7-24-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Earth Sciences

Concentration

Geophysics

Committee Chair

Charles Langston

Committee Member

Christine Powell

Committee Member

Robert Smalley

Committee Member

Mitch Withers

Abstract

Part 1: A phased array of 19 broadband seismometers was deployed from November 2009 to September 2011 to detect nonvolcanic tremor associated with the Reelfoot fault. An autodetection algorithm using broadband frequency–wavenumber analysis was used to search for the recurrence of signals. The original signals, detected in 2006, appeared as short duration, impulsive arrivals with a high phase velocity. We identify thousands of signals during the experiment. Two azimuthal peaks are observed arriving from the west and northeast. The detections are similar to the events seen in 2006 and are inferred to come from very small ML=-1 microearthquakes occurring in shallow basement faults. Most signals arrive with coherent S-wave energy which implies very small local and regional earthquakes. Other signals show distinct changes in slowness and azimuth as a function of time. These events were interpreted as atmospheric acoustic sources. The high-frequency content and impulsive arrivals of the nonacoustic arrivals are not consistent with traditional tectonic tremor but indicate seismic activity in the crust near the Reelfoot thrust fault.Part 2: Waveforms from the Eastern Tennessee Seismic Network are corrected to the nominal Wood–Anderson (WA) torsion seismometer to obtain a total of 11,905 amplitudes to determine a local magnitude scale for the Eastern Tennessee Seismic Zone (ETSZ). We obtain the following distance correction function:-log10(A0)=0.538log10(r/17)−0.0002516(r-17)+2.0 from our inversion. The -log10(A0) is very flat at distances > 200  km, suggesting low distance attenuation at local and near-regional distances. The b-values for the currently reported duration magnitude is 0.9.Part 3: Dispersion measurements obtained from ambient noise tomography and earthquake data are combined with radial receiver functions from 134 stations to invert for a high resolution shear-wave velocity model of the ETSZ. We obtain velocities models to depths of 200 km to obtain information about the structure of the crust and upper mantle. We detect a strong velocity contrast across the vertical projection of the New York –Alabama lineament which we attribute to an ancient strike-slip fault. We also observe a low-velocity zone in the upper mantle which could be the base of the continental lithosphere in this area. The majority of the depths of this low velocity zone begin around 125 km.

Comments

Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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