S41D-01 INVITED
An over view of ground-based electromagnetic observations addressed to seismo- electromagnetism in Japan
Almost all through the human history, electromagnetic (EM) phenomena associated with earthquakes (EQ) have been repeatedly reported. Especially 1995 Kobe earthquake brought a great impact to the earthquake prediction studies in Japan. After this devastating event, Science and Technology Agency (STA) decided to initiate five year programs of Earthquake Frontier Program which included RIKEN/NASDAfs subprograms. Both subprograms addressed to the short-term earthquake prediction research by using the electromagnetic methods, and the main objective was to attain comprehensive understanding of the pre-, co- and post seismic EM phenomena related to EQs. Both projects produced many appraisable results. However, there is still a long way to go, physics of DC to ULF/ELF signal generation/transmission and so on. We now consider that EQ related EM signals may be classified into two major groups. One is EM signals supposedly emitted from the focal zone and the other is anomalous transmission of EM waves over the epicentral region. Of-course, to establish the science of seismo-EM phenomena, we need continued efforts to collect and accumulate more data on one hand and to advance basic physics on the other. In the presentation, we briefly summarize the current status of ground-based EM measurements from ULF to VHF ranges in Japan (DC-ULF geoelectric potential difference, ULF, ELF and VLF three-component magnetic, VLF, LF and VHF anomalous transmission of radio waves, etc.) and propose the future direction (tactics) of EQ- related EM study in Japan.
S41D-02
The 1989 Ms 7.1 Loma Prieta, California, Magnetic Earthquake Precursor Revisited
Repeatable prediction of individual large earthquakes on the basis of quantitative geophysical data has proven to be frustratingly difficult and fraught with controversy. Still, some claims of success have been published, and among these are reports of identifiable precursory changes in magnetic-field activity as measured by ground- based magnetometers. By far the most prominent of such claims is that of Fraser-Smith et al., GRL, 17, 1465- 1468, 1990 who identified changes in Ultra Low Frequency (ULF, 0.01-10 Hz) magnetic noise prior to the 18 October 1989 Ms 7.1 Loma Prieta, California earthquake. The Fraser-Smith et al. result has been frequently cited in the literature, and it has been a major motivational influence for new research programs involving large arrays of ground-based instruments and even some satellite-based systems. We re-examine the data of the reported precursor, comparing them against independent data collected by magnetometers located in Japan and in the United States at the time of the Loma Prieta earthquake. From our analysis we infer that the key components of the precursory signal identified by Fraser-Smith et al. can be explained by minor corruption of the data in the form of a gain enhancement and time-stamp missassignment, possibly due to digital processing errors or inadvertent post-acquisitional treatment. We conclude that the reported magnetic anomaly is not related to the Loma Prieta earthquake. http://geomag.usgs.gov/
S41D-03
Re-affirming the Magnetic Precursor to the 1989 Loma Prieta, CA, Earthquake Using Magnetic Field Data Collected in the US in 1989 and 1990
Electromagnetic (EM) signals are one of the most commonly claimed precursors to earthquakes. The most cited of these proposed EM events is the report of ultra-low frequency (ULF) EM anomalies prior to the 10/17/1989 magnitude 7.1 Loma Prieta earthquake (Fraser-Smith et al., 1990, GRL 17, 1465) recorded at Corralitos (7 km from the epicenter). Although some critical aspects of this ULF-EM signal (such as the increase of amplitude at lower frequency) are entirely consistent with an origin for the signal at the earthquake hypocenter, some scientists question the validity of the data simply because only a single instrument recorded the signal. Recently, W.H. Campbell (2005, Eos Trans. AGU, 86(18), Jt. Assem. Suppl., Abstract GP23A-01; and unpublished manuscript) has claimed that the existence of a ULF precursor signal to the Loma Prieta earthquake "is very likely false". Campbell argues that the reported "precursor" was not of local origin but was recorded throughout the western US and was therefore a solar-terrestrial disturbance; and that the extreme amplitudes reported by Fraser-Smith must have been due to a change of gain of the Corralitos magnetometer "by a factor of 5 to 10, on (or about) 4 to 5 October", i.e. an instrumental malfunction. J.N. Thomas et al. (2007, Abstract 4036, XXIV General Assembly IUGG, Perugia; and unpublished manuscript) repeat and amplify this claim. Because of the importance of the Loma Prieta ULF-EM signal to earthquake-prediction studies, we have critically examined the Campbell and the Thomas et al. claims about the veracity of the signal. Campbell made a visual comparison/correlation of the magnetic signals recorded at Corralitos with those recorded at U.S.G.S. magnetic observatories at Fresno, Boulder and Tucson, but only for the first 18 days of October 1989. Thomas et al. made numerical correlations of data from Fresno and Kakioka, Japan, with the Corralitos data-set, but only from September 18 through October 27, 1989. We have duplicated much of the Campbell and the Thomas et al. methodologies, but we are extending our comparison over two years of observations including time periods significantly before and after the Loma Prieta earthquake. Even a simple visual comparison between very long time series from Fresno and Corralitos shows that the single instrumental gain change postulated by Campbell and by Thomas et al. does not suffice to explain the data. Unless one postulates multiple fluctuations of instrumental response, with time-varying gain, the simplest explanation of the Corralitos magnetic field anomalies is that some form of ULF precursor was recorded prior to the Loma Prieta earthquake.
S41D-04
The Large-Amplitude ULF Magnetic Fields Preceding Large Earthquakes: Merely the "Tip of the Iceberg"?
It is now around 400 years since it was first recognized that there was a slowly-time-varying "magnetic signal" emerging out of the Earth (i.e., the Earth's magnetic field), but until very recently the competition from ultra-low frequency (ULF, f ≤ 10 Hz) magnetic signals originating in the upper atmosphere has made it difficult to identify other different types of ULF signals originating in the Earth. The four independent published reports of large-amplitude ULF magnetic fields preceding large earthquakes currently available now provide evidence for another source of these fields within the Earth; the presumed earthquake-related fields being large enough to appear above the upper-atmospheric noise background. An obvious inference from this result is that there may be other processes within the Earth generating ULF magnetic signals that are not big enough to be detected above the upper atmospheric noise background. Fortunately this latter noise tends to be uniform over large distances on the Earth's surface and can be removed by simple cancellation techniques using either pairs or arrays of identical, spaced measurement systems. ULF magnetic field measurements made in 1994 will be used to demonstrate that there are indeed residual components that remain after cancellation that may well originate in the Earth. If so, the presumably earthquake-related ULF magnetic fields are merely the "tip of the iceberg" providing us a limited glimpse through an unexploited window into the Earth. Magnetometers and magnetic-field gradiometers of the greatest sensitivity and with broad frequency responses are obvious keys to exploring the processes glimpsed through this tantalizing new(?) window.
S41D-05 INVITED
LAIC Model a New Source of Information for Seismo-Tectonics
The Lithosphere-Atmosphere-Ionosphere Coupling model developed recently together with experimental data used for the model validation put forward the doubtless and urgent need to reconsider our understanding of the earthquake preparation process in its latest stage (one-two weeks before the seismic shock). The three major results are the following: 1. The thermal and ionospheric anomalies observed by the remote sensing satellites for all recent major earthquakes demonstrate that the area affected by the earthquake preparation process is quite large (the linear size is from few hundred up to thousands of kilometers) 2. The area of earthquake preparation includes not only the region of epicenter of impending earthquake but also the active tectonic faults and the borders of tectonic plates one of which is the plate where epicenter is situated and others are the adjacent plates. 3. The temporal dynamics of the thermal, and atmospheric anomalies as well as their altitude distribution from the ground surface up to the Top Of the Atmosphere (TOA), the estimated thermal energy released imply that they are produced by the air ionization process and the only source for such ionization is the alpha radioactivity of radon. One should not obligatory return to the dilatation theory which considered the large earthquake preparation areas but at the same time should to accept that tectonic stress and corresponding deformation of the crust are increasing within the interval of two weeks before the seismic shock over the large area up to the borders of interacting tectonic plates. The pre earthquake thermal anomalies consistently observed over different seismo- tectonic regions (having different crust structure) confirm the existence of radon variability to initiate the observed anomalies. Presentation will provide valuable source of information for planning the ground based gas released monitoring, radon observation and atmospheric/ionospheric interpretation related to active faulting and earthquake preparation process.
S41D-06
How can Stresses in the Earth's Crust Lead to Bursts of Electromagnetic Signals?
It is by now quite well established that igneous and high-grade metamorphic rocks in the Earth's crust generate electric currents when subjected to deviatoric stresses. The reason is that these rocks contain dormant electronic charge carriers in the form of peroxy links. Peroxy links are sites in the crystal structures of the constituent minerals where oxygen anions have converted from their common 2- valence state to the 1- valence state, O3X- OO-XO3 with X=Si4+, Al3+ etc. As rocks are stressed and dislocations sweep through the mineral grains, the peroxy links break up, activating electrons and pholes ("phole" is an abbreviation for "positive hole", a defect electron on the oxygen sublattice, chemically O in a matrix of O2). While the electrons are confined to the stressed rock volume, the pholes are mobile electronic charge carriers that can spread out of the stressed rock into the surrounding unstressed rocks. They travel via energy levels at the upper edge of the valence bands. They flow readily through 3+ m of rocks in the laboratory and are believed to be able to flow through kilometers of rocks, probably 10s of kilometers in the field. Laboratory experiments suggest that every cubic kilometer of stressed rock has the capacity to generate currents on the order of 10,000-100,000 amps, flowing for hours and days. The situation is akin to a battery, where the stressed rock takes on the role of the anode, while the unstressed rocks act as the electrolyte. However, stressing rocks does not yet produce a battery current. An additional requirement is that a conductive path be established which enables electrons from the stressed rock volume to also flow out, meet and reconnect with the pholes at the cathode. In the laboratory this condition is easily met by running a wire from a Cu contact attached to the stressed rock to a Cu contact attached to the unstressed rock. In Nature, however, this closure of the battery circuit has to be achieved by different means. Two possibilities are: (i) the phole current flows into an aquifer or brine-saturated gouge of a fault, (ii) the stressed rock volume extends downward into the hot, electronically conductive lower crust, allowing electrons to flow out. Which of the two scenarios applies, and at which point in time the circuit closes, will determine whether or not, when andŽ how large battery currents can flow. The fact that not every major earthquake produces detectable EM signals attests to the complexity of the system.
S41D-07 INVITED
The First Results About Earthquake Study with FORMOSAT-3/COSMIC
To improve the global weather prediction and space weather monitoring, six microsatellites termed the Formosa Satellite 3 - Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) were launched into a circular low-Earth orbit (LEO) from Vandenberg Air Force Base, California, at 0140 UTC on 15 April 2006. Each microsatellite of the joint Taiwan-US satellite constellation mission has a GPS occultation experiment (GOX) payload to operate the atmospheric and ionospheric radio occultation, a tiny ionospheric photometer (TIP) to observe the nighttime ionospheric airglow OI 135.6 nm emission, and a tri-band beacon (TBB) to tomographically estimate fine structures of ionospheric electron density on the satellite-to-receiver plane. While the GOX daily observes about 2500 vertical electron density profiles up to the satellite altitude, the TIP provides accurate horizontal gradients of nighttime electron density. In this study, anomalies in the ionospheric electron density structure and dynamics concurrently observed by FORMOSAT-3/COSMIC and co-located ground- based GPS receivers before recent large earthquakes are presented and discussed.
S41D-08
Geomagnetic dependence of ionospheric disturbances induced by tsunamigenic internal gravity waves
A series of ionospheric anomalies following the Sumatra tsunami has been recently reported in the literature (Liu et al. 2006; DasGupta et al. 2006; Occhipinti et al. 2006). These anomalies show the signature in the ionosphere of tsunami-generated internal gravity waves (IGW) propagating in the neutral atmosphere overlooking the ocean. All these anomalies, observed in the total electron content (TEC) measured by GPS or altimeters, show geographical heterogeneity in the perturbed TEC amplitude and suggest a dependence of geomagnetic latitude. This latter, never treated theoretically, have been taken into account in the 3D modeling of Occhipinti et al. (2006) and used for the interpretation of the TEC Topex and Jason data. The same quantitative modeling is used here to focus on both, the magnetic field dependence and the geometrical properties of the tsunami wave. The etherogenity produced in the ionosphere by a north-ward and south-ward tsunami propagation propagation in the global scale is presented here in term of TEC perturbations. The sensitivity of both altimeters and base-ground GPS is analyzed and the modeling results are used to discuss the role of ionospheric sounding in the future oceanic monitoring and tsunami warning system. [DasGupta et al., 2006] Earth Planet. Space, 35, 929-959. [Liu et al., 2006] J. Geophys. Res., 111, A05303. [Occhipinti et al., 2006] Geophys. Res. Lett., 33, L20104, 2006