Exploration of the lower lithosphere; northeastern United States

Details Exploration of the lower lithosphere; northeastern United States Exploration of the lower lithosphere; northeastern United States

Feb 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992pepi...70...22h&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 70, Issue 1-2, p. 22-38.

Physics

4

Scientific paper

In this study we report on the modeling of broadband seismograms from moderate-sized earthquakes at regional distances. We demonstrate that the longer-period motions (World Wide Standardized Seismograph Network; WWSSN) preceding the direct S arrival can be modeled reasonably well with a crustal model consisting of a layer over a half-space. Although a generic model, assumed to be the same everywhere, can be used to model the Pnl waveshape, some adjustments are required to fit the Pn and Sn timing for specific paths. Inversion of three-component seismograms assuming such simple models proves effective in source retrieval using a single station. Shorter periods can then be modeled by adding more detail to the velocity structure, holding the source fixed and repeating the process.
Application of this modeling procedure to earthquakes occurring in the New England region proves interesting. In particular, paths on opposite sides of the Appalachian Thrust Belt produce distinct models. Paths along the western side of the belt can be modeled with an average crustal thickness of 35 km, the compressional and shear velocities of the crust are 6.5 km s-1 and 3.6-3.7 km s-1, and those of the upper mantle 8.4-8.5 km s-1 and 4.7-4.8 km s-1, respectively. The results are in agreement with the normal shield parameters. Paths along the eastern side of the belt indicate more variability but yield consistently lower lithospheric velocities by 3-4% for P waves. These models predict P-wave travel time delays across this zone of about 0.3 s, in agreement with teleseismic delays.

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