Overview


ESEE is a joint U.S. Geological Survey - CERI project designed to study the excitation and propagation of Rayleigh Waves in the unconsolidated sediments of the Mississippi Embayment.  Two borehole explosion sources will be detonated to generate surface waves in the southern New Madrid Seismic Zone (NMSZ) near Marked Tree, AR, and in the northern NMSZ near Tiptonville, TN.

The southern explosion will be 2600 lbs and the northern 5000 lbs.

Observations of surface waves from these explosions will greatly constrain estimates of anelastic attenuation in the sediments.  Past estimates of anelastic attenuation from earthquake body wave studies and refraction studies are so great that they would imply no appreciable high frequency surface wave propagation within the embayment.  However, recent small exposion studies and analysis of analog data from a 1991 U.S.G.S. explosion show that surface waves do indeed propagate in the embayment implying a major problem in characterization of anelastic attenuation.

The scientific hypothesis is simple - anelastic attenuation in the unconsolidated sediments of the Mississippi embayment is significantly lower than previously believed (i.e., Qp and Qs are significantly higher).

The test of the hypothesis is the simple observation of Rayleigh waves from the explosions recorded at  broadband seismic stations at distances greater than 10 kilometers.

If the data are consistent with the hypothesis, then sediments of the Mississippi embayment will tend to amplify high frequency ground motions from future large earthquakes in the NMSZ increasing estimates of hazards due to strong ground motions.

Data will be collected from stations of the CERI Cooperative Network and from at least 9 temporary broadband stations that fill in network gaps (Figure 1) .  In addition, an array of at least 9 K2 accelerographs will be deployed at each explosion to record near-source body and surface waves.


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