Dst Storm Index

Scientists are concerned with the local accuracy of the representation of geomagnetic storms by the Dst index. Using records from a 1990 longitude line of stations through central Australia (from Darwin to Port Augusta) together with the permanent observatories near the four corners of that country, the differences between the Australian recorded fields and the index were

mafic rock Hoo<J Bremerton outcrop cana.

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mafic rock Hoo<J Bremerton outcrop cana.

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20-100 1 00-400

FIGURE 5.8 ► This cross section is a two-dimensional model of transverse magnetic mode magnetotelluric (MT) data from a profile across the Olympic Peninsula of western Washington state. MT soundings were obtained at the numbered locations. The west end of the profile is near the coastline and the east end terminates on the west side of Puget Sound at Bremerton. The main focus of this MT profile was the study of the thick mafic rocks, which occur here and which have been found in other MT studies to have resistivities of 150-2000 ohm-meters. The release of tectonic stresses within the mafic rocks gives rise to numerous small earthquakes (shown by black dots) that are concentrated in the mafic rocks at depths of 10-20 km. More conductive rocks of less than 100 ohm-meters in the cross section are related to Tertiary and Quaternary sedimentary rocks. Intermediate values of resistivity may be related to some of the mafic rocks and to interfingered mafic rocks and sedimentary rocks. Figure from Dal Stanley of USGS.

determined (Figure 5.10). The storm fields throughout that country were quite similar in appearance; thus, they were not due to local anomalies. There were often large local storm field differences from the index.

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