Schmucker, 1970 (Scripps) - MTNet

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Bulletin. Scripps Institution of Oceanography
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Ava.2I. 19611
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Fig. 13. Two bays as recorded on the profile San Clemente Island-Tucson through
southern California. Prominent Z-variations a t the coastal station La Jolla gradually
diminish toward the open ocean and toward inland. Slight reduction"of the D-amplitude
near the coast in comparison to the D-amplitude at Tucson.
As already stated by Parkinson, coastal anomalies could arise from different
mantle conductivities under continents and oceans. It would imply that
a steep uplift of highly conductive material occurs along the continental slope,
bringing deep induction currents near to the surface below the sea floor. On
the other hand, these anomalies coincide with an outstanding superficial conductivity
contrast and they could be "edge effects" of oceanic eddy currents
which cannot penetrate into the less conducting continental surface layers and
are forced to flow parallel to the coastlines.
Because of the complicated coastal structure in southern California it was
decided to conduct similar observations in central California, where the continental
shelf is just 100 km wide. The station on the Farallon Islands offshore
San Francisco was even within 40 km of the continental slope. Three
lines of field stations were set up perpendicular to the coast and extending
about 400 km inland. These profiles crossed three geological structures,
(a) the California coast range, (b) the San Joaquin valley, (c) the Sierra
Nevada (fig. 21). It should be noted that the San Joaquin valley is a young
embayment, filled with unconsolidated sediments of presumably high conductivity,
in contrast to the poorly conducting granitic bloc of the Sierra
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