During the past 5 years, few new indications of convincing longer-term tectonomagnetic
events (i.e., durations greater than minutes to weeks) are apparent in
multiple near-field magnetometer records obtained along active faults as a result
perhaps of strain redistribution prior to moderate/large earthquakes (see, for example,
Figure 3 (Lower) above). These signals either are rare or do not generally
have amplitudes greater than a nanotesla or so. If signal amplitudes are less than
a nanotesla, it is unlikely that any reported precursive signals at great distances
from these earthquakes are truly earthquake related. Long term relatively uniform
changes, apparently related to crustal loading have been previously reported
(Johnston, 1989; Oshiman et al., 1983).