Schmucker, 1970 (Scripps) - MTNet

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32 Bulletin, <strong>Scripps</strong> Institution of Oceanography 3. 17 Analysis of Diurnal Variations and Pulsations Hourly means, centered on the full hour, were derived from local midnight to local midnight on eight quiet days (if available) for each line of survey stations and then averaged over these days. After the removal of the noncyclic trend the resultant hourly values were harmonically analyzed in the usual manner (cf. chap. 16 in "Geomagnetism"). Temperature effects diminished the Significance of the 1 st harmOniC, while the consistent behavior of the 2nd and 3rJ harmonic showed that they are essentially free from such contaminations (see tabs. 11-15). No attempts have been made to separate or to correlate any anomalous part of the observed diurnal variations, even though local anomalies of internal origin were clearly recognized at many sites. The time resolution of the records of about one minute did not allow a detailed analysis of pulsations, based on continuous scalings. Instead, peakto-peak values were measured, separately for each survey station and regardless of time lags between peaks of the three components. This left in particular the horizontal orientation of the disturbance vector undetermined. The peak values thus obtained were squared and averaged over about ten pulsations or pulsation trains of roughly the same period. Denoting these squared averages with sD' sH, sz, the mean ratio of vertical to horizontal pulsation amplitude equals for that particular period and survey station (tab. 16). (3.40)
4. DESCRIPTION OF THE ANOMALIES 4. 1 Introduction The first six months of field operations (January to June 1960) were carried out on a 1000 km east-west profile through the southwestern states, crossing the Southern Rockies, the Rio Grande valley, and extending deep into West Texas (fig. 2). The second phase of the program (November 1960 to February 1962) was devoted to a detailed survey in southern and central California with inclusion of the eastern slope of the Sierra Nevada. The encountered anomalies of geomagnetic variations are now described in geographical order and each anomaly is illustrated by selected magnetograms. Their final interpretation follows in chapter 7. The results of the statistical data reduction are listed in tables 5 to 16. . 4.2 Rio Grande Anomaly of Bays and Other Fast Disturbances The survey was started near Tucson, Arizona, which is well-known for its small Z-variations during bays and magnetic storms (Bartels et aI., 1939). This indicates a horizontally stratified conductivity distribution with high conductivities near the surface. Equally subdued Z -variations were found at several field stations around Tucson (NOG, SEL, RAY, COC). The "Tucson-type" Z -variations end about 400 km east of Tucson. Between Las Cruces and Cornudas the Z -amplitude of bays and storms increases about threefold relative to Tucson. The Z -variations remain of this intensity as far east as Sweetwater, Texas, which was the most eastern survey station (fig. 7). Already a visual inspection of the traces reveals that the increased Zvariations east of the Rio Grande resemble in their appearance those in D. This indicates that a north-south striking conductivity structure is the underlying cause for the anomalous behavior of Z, parallel to the Rocky Mountain front in New Mexico. The increased Z -amplitude does not seem to be restricted to a limited area, since no equivalent to the subdued "Tucson-type" Z -variations has been found in West Texas. Hence, we have here a regional change of the internal part of bays. The increased Z -variations at Sweetwater as well as the reduced Z -variations at Tucson are both considered to be "normal" in the sense that these stations lie within regions of stratified but different internal structures with high mantle conductivities west and low mantle conductivities east of the Rio 33
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APPENDIX. I (To SECTION 3.6) Trend
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EXPLANATIONS FOR PLATES I-VI The pl
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