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A Time-Term Interpretation of the First-Arrival Data of the 1963 Lake Superior Experiment

2011; American Geophysical Union; Linguagem: Inglês

10.1029/gm010p0166

2328-8779

Michael J. Berry, G. F. West,

Geophysics and Gravity Measurements

The first-arrival data of the Lake Superior Experiment of 1963 have been interpreted by the time-term method, which analysis has shown to be well suited to this type of survey, and the results appear to be consistent and meaningful. Approximately 500 first arrivals from head waves generated at the Mohorovičić discontinuity have been reduced to estimates of crustal time terms at more than 100 locations. A much shallower refracting surface, here called the upper refractor, furnished nearly 1000 observations to yield upper-crustal time terms at the same locations. The analysis reveals the material beneath the upper refractor and beneath the M discontinuity to have velocities of 6.63 and 8.10 km/sec, respectively. On the basis of a simple interpretation of the time terms, the surface of the upper refractor is revealed as undulating, coming close to the surface at the edges of the lake, and reaching maximum depths (not exceeding 15 km) to the east and west of the Keweenaw Peninsula. On a similar basis the M discontinuity is revealed as an easterly dipping surface, having a depth of approximately 35 km at the west end of the lake and reaching a maximum depth of about 60 km in the region just west of the Keweenaw Peninsula. Eastward, the time-term values fluctuate but do not increase or decrease systematically.