| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
GEOPHYSICS LABORATORY UNIVERSITY OF TORONTO, TORONTO, Canada
Abstract
The first-arrival data of the Lake Superior Experiment of 1963 have been interpreted by the time-term method. The analysis has shown the method 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 Mohorovi
i
discontinuity, have been reduced to estimates of crustal time-terms at over 100 locations. A much shallower refracting surface (here called the Upper Refractor) furnished nearly 1,000 observations to yield upper crustal time-terms at the same locations. The analysis reveals the material beneath the UR and beneath the M to have velocities of 6.63 and 8.10 km/sec respectively. The surface of the Upper Refractor, on the basis of a simple interpretation of the time-terms, is revealed as undulating, coming close to the surface at the edges of the lake and reaching maximum depths of approxmately 15 km to the east and west of the Keweenaw Peninsula. On a similar basis the Mohorovii 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. Eastwards, the time-term values fluctuate but do not increase or decrease systematically.
The velocity of the material lying above the Upper Refractor is not well determined, but appears to be roughly 5.5 km/sec. A perusal of geological literature suggests that this low velocity material is mostly sedimentary, filling a well-known synclincal basin whose axis bends around the Keweenaw Peninsula. This mainly sedimentary section is known to be underlain by a great thickness of igneous rocks, which in all probability corresponds to the Upper Refractor mapped by the seismic studies.
This article has been cited by other articles:
|
|
 |
|
  J. R. KAYAL and R. DE Pn velocity study using a temporary seismographic network in the Shillong Plateau, Northeast India Bulletin of the Seismological Society of America, October 1, 1987; 77(5): 1718 - 1727. [Abstract] [PDF]
|
|
|
|
|
|
W. M. KOHLER and G. S. FUIS Travel-time, time-term, and basement depth maps for the Imperial Valley region, California, from explosions Bulletin of the Seismological Society of America, October 1, 1986; 76(5): 1289 - 1303. [Abstract] [PDF]
|
|
|
|
|
|
C. E. ZERVAS and R. S. CROSSON Pn observation and interpretation in Washington Bulletin of the Seismological Society of America, April 1, 1986; 76(2): 521 - 546. [Abstract] [PDF]
|
|
|
|
 |
|
 J. J. DOODY and M. BROOKS Seismic refraction investigation of the structural setting of the Lizard and Start complexes, SW England Journal of the Geological Society, January 1, 1986; 143(1): 135 - 139. [Abstract] [PDF]
|
|
|
|
|
|
L. H. JAKSHA and D. H. EVANS Reconnaissance seismic refraction-reflection surveys in northwestern New Mexico Bulletin of the Seismological Society of America, August 1, 1984; 74(4): 1263 - 1274. [Abstract] [PDF]
|
|
|
|
|
|
J. N. MURDOCK Seismic velocity structure of the metamorphic belt of central California Bulletin of the Seismological Society of America, February 1, 1980; 70(1): 203 - 221. [Abstract] [PDF]
|
|
|
|
|
|
T. MATUMOTO, M. OHTAKE, G. LATHAM, and J. UMANA Crustal structure in Southern Central America Bulletin of the Seismological Society of America, February 1, 1977; 67(1): 121 - 133. [Abstract] [PDF]
|
|
|
|
|
|
R. L. MCCOLLOM and R. S. CROSSON An array study of upper mantle velocity in Washington State Bulletin of the Seismological Society of America, April 1, 1975; 65(2): 467 - 482. [Abstract] [PDF]
|
|
|
|
|
|
R. L. WESSON, J. C. ROLLER, and W. H. K. LEE Time-term analysis and geological interpretation of seismic travel-time data from the Coast Ranges of central California Bulletin of the Seismological Society of America, August 1, 1973; 63(4): 1447 - 1471. [Abstract] [PDF]
|
|
|
|
|
|
S. A. D. BAMFORD Applications of simulated data studies to crustal refraction seismology Bulletin of the Seismological Society of America, August 1, 1971; 61(4): 1013 - 1031. [Abstract] [PDF]
|
|
|
|
|
|
R. M. HAMILTON Time-term analysis of explosion data from the vicinity of the Borrego Mountain, California, earthquake of 9 April 1968 Bulletin of the Seismological Society of America, April 1, 1970; 60(2): 367 - 381. [Abstract] [PDF]
|
|
|
|
|
|
L. REITER An investigation into the time term method in refraction seismology Bulletin of the Seismological Society of America, February 1, 1970; 60(1): 1 - 13. [Abstract] [PDF]
|
|
|
|
|
|
R. F. MEREU and J. A. HUNTER Crustal and upper mantle structure under the Canadian Shield from Project Early Rise data Bulletin of the Seismological Society of America, February 1, 1969; 59(1): 147 - 165. [Abstract] [PDF]
|
|
|
|
|
|
R. W. E. GREEN and A.L. HALES The travel times of P waves to 30{degrees} in the central United States and upper mantle structure Bulletin of the Seismological Society of America, February 1, 1968; 58(1): 267 - 289. [Abstract] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
