Mysterious tremor-like signals seen on the reelfoot fault, Northern Tennessee


A phased array of 19 broadband seismometers was deployed from November 2009 to September 2011 in an effort to detect nonvolcanic tremor or tectonic tremor associated with the Reelfoot fault, northern Tennessee. An autodetection algorithm using broadband frequency–wavenumber analysis was used to search for the recurrence of signals first reported during an active source experiment in 2006. The original signals appeared as short duration, impulsive arrivals with a high phase velocity ranging from 3 to 25 km=s.We have identified thousands of similar signals on the 2-year long array data. Two distinct detection peaks are observed with event azimuths from the west and northeast. The detections are most similar to the events seen in 2006 and are inferred to come from very small (ML ~ −1) microearthquakes that occur in the shallow basement on faults adjacent to the Reelfoot fault. These include detections with coherent S-wave energy that reinforce the interpretation of very small local and regional events. Other signals detected 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 tectonic tremor as seen in other parts of the world but do indicate seismic activity in the crust near the Reelfoot thrust fault that was previously unknown.

Publication Title

Bulletin of the Seismological Society of America