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U.S. Geological Survey Crustal Studies Technical Letter Number 23

In cooperation with the Defense Advanced Research Projects Agency

A Preliminary Summary of a Seismic-Refraction Survey in the Vicinity of the Tonto Forest Observatory, Arizona

By J.C. Roller, W.H. Jackson, D.H. Warren, and J.H. Healy

1964

Thumbnail of and link to report PDF (25.8 MB)Abstract

The U.S. Geological Survey complete d a seismic-refraction survey in the vicinity of the Tonto Forest Seismological Observatory (T.F.S.O.) in April and May 1964. More than 1200 km of reversed profiles were surveyed to determine the crustal structure and crustal and upper mantle velocities in this area. The purpose of this work was to provide information on wave-propagation paths of seismic events recorded at T.F.S.O. and to improve the performance of the Observatory in locating and identifying these events.

First arrivals indicate that the Mohorovicic discontinuity dips to the northeast by as much as 6 degrees under T.F.S.O., and may even be displaced vertically by as much as 5 km immediately north of the Observatory near the boundary of the Basin and Range a n d t he Colorado Plateau Provinces.

A preliminary examination of the first arrivals indicates that the crust at T.F.S.O. is at least 30 km thick and is made up of at least two seismic layers. A thin veneer at the surface with a velocity of approximately 4 km/sec is underlain by a layer with a velocity of approximately 5.9 km/sec to 6.1 km/sec. An intermediate layer with velocity of 6.6 to 7.0 km/sec is probably present in the lower crust, but is not revealed by first arrivals. The velocity of seismic waves in the upper mantle is about 7.9 km/sec.

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Menlo Park, California 94025
http://earthquake.usgs.gov/

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Suggested citation:

Roller, J.C., Jackson, W.H., Warren, D.H., and Healy, J.H., 1964, A Preliminary Summary of a Seismic-Refraction Survey in the Vicinity of the Tonto Forest Observatory, Arizona: U.S. Geological Survey Crustal Studies Technical Letter Number 23, 57 p. (Available at https://pubs.usgs.gov/misc/tl/0023/.)



Contents

Abstract

Introduction

Preliminary Results

Summary

References

Appendixes 1–2


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