IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS009 Oral Presentation 2030
Some basic problems related to ground based seismo-electromagnetics
Prof. Seiya Uyeda
1. Anomalies immediately before earthquakes (EQs) When the lead time of alleged EM precursors are
long, they may be less convincing. However, when anomalies are observed minutes before EQs, it
would be much more convincing. We introduce such anomalies (pulses of msec duration) observed by
the VAN group for a long time. 2. Co-seismic anomalies One of the most common objections to
seismo-EM is no co-seismic signals. In fact, although signals at the time of EQ have been routinely
observed, they were always observed only when seismic waves arrived. They are co-seismic wave
signals. So far, therefore, it is true that no reliable true co-seismic signals have been observed. If true
co-seismic signal does not exist, can that be a reason for denial of pre-seismic signals Not necessarily.
It can rather provide key information for understanding the mechanism of EQ and seismo-EM. Certainly
lab experiments show high frequency EM emission at rock fracture, which suggests the same may
happen at EQ. However, high freq. signals at focal depth would not reach earth surface. Even if they
do, usual DC-ULF field apparatus cannot record them. This is one explanation for non observation of
true co-seismic signals. However, there may be a flaw in this: since fracture along faults of large EQ will
take some time, measurable low freq. convolution component will inevitably be generated. This might
lead to the conclusion that EQ does not generate even high freq. signals, possibly because EQ is not
fracture but sliding of existing faults. Although this view is not warranted at the moment as information
on EM effects of fault sliding with high speed at EQ is scanty, it might open new perspectives. In any
case, EQ is a stress releasing event whereas precursory phenomena occur during the slow stress
increasing process. They are different physical processes. 3. No pre-seismic EM signals at 2004 M6
Parkfield EQ. USGS scientists state that since nothing was observed at Parkfield, EM in general is
unlikely useful for short-term prediction. Although we have some doubt about their methodology and
data analysis, here we tentatively accept their results and seek some reason for non existence of EM at
Parkfield and existence elsewhere. One possibility is as follows: San Andreas Fault is known for its
weakness. Therefore, it may be suspected that EQ takes place before any EM signal is generated. For
generation of DC-ULF precursory EM signals, two main models are suggested. One is the solid state
physics model by the VAN group and the other is the more popular electrokinetic model. Both models
need certain level of stress to operate, which may be higher than San Andreas Fault can sustain.
Keywords: pre seismic pulses, co seismic anomalies, parkfield