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Tectonomagnetism and tectonoelectricity
Author(s) -
Johnston M. J. S.
Publication year - 1987
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg025i005p00983
Subject(s) - geology , seismology , magnetometer , volcano , geophysics , fault (geology) , extrusive , ambient noise level , active fault , magnetic field , geomorphology , physics , quantum mechanics , sound (geography)
The last four years has seen a considerable waning of efforts in the U.S. to use the inherent stress sensitivity of the magnetization of rocks in tectonically active regions as a tool for understanding and, perhaps predicting, earthquake activity and volcanic eruptions. The primary reasons for this decreased interest derive from accumulating evidence that the mean deviatoric stress release during earthquakes (and the ambient shear stress near active faults) is lower than than had been previously assumed and, secondly, the observational limits of magnetometers separated by about 10 km, after application of a variety of noise reduction techniques, appear to be no better than about 0.1 nT. Lower estimates of the average change in deviatoric stress associated with earthquake rupture correspondingly reduce the fields calculated from tectonomagnetic models. At the same time, some unexpected and exciting results have been obtained which indicate many aspects of magnetic field changes near active faults and volcanoes are still not completely understood. The more important of these results are: 1) the observation of correlated magnetic, strain, uplift, and gravity changes during the latter stages of a remarkable deformation episode near the San Andreas fault in southern California, 2) indications of anomalous change in magnetic fields along the San Andreas fault to the southeast of Palm Springs, 3) an unambiguous observation of a volcanomagnetic effect at Mt. St. Helens prior to an extrusive eruption, and 4) the first observations of coseismic seismomagnetic effects on two independent magnetometers during the July 8, 1986, M L 5.9 North Palm Springs earthquake. A resurgence of interest has occurred during the quadrennium in a related area concerning electrical phenomena and electromagnetic effects related to earthquakes and volcanoes. Mechanisms have been proposed to explain the occurrence of earthquakes lights and the possibility of electromagnetic emission prior to the 1960 Chilean earthquake has been proposed. Self potential anomalies have been observed before and during several eruptions on Kilauea volcano in Hawaii.