T51B-0444 0800h
Large-Scale Model of the Electrical Conductivity in the Crust
Pre-earthquake electromagnetic signals have been linked to large currents (10$^{6}$ A) and large propagation distances (100 km). From physical principles, such signals require charge motion. Once generated, the charges must be able to move in the ground. This motion is governed by the electrical conductivity in the source volume of the charges and in its vicinity. There are different proposed contributions to the conductivity of the crust. These include interconnected pore water, conductive minerals like magnetite, sulfides, and other impurities, and partial melts. The intrinsic conductivity of the rocks is generally thought to be too low to make an important contribution. In order to build a proper model, the scale of the phenomenon must be considered. We consider situations where contributions from two materials dominate. The conductors are saline solutions and the igneous rocks themselves. The model considers thick layers of rocks and thin sheets of brine-filled fissures oriented in vertical planes. The two primary axes of conduction are normal and parallel to the planes. The conduction problem is thus reduced to that of series and parallel resistors whose total conductivity is related to the volume of each constituent. In addition the conductivity is depth-dependent. The upper crust tends to be crisscrossed by brine-filled fissures, while the deeper crust tends to be fluid-free due to retrograde mineral reactions, which consume water. Depending on the density of fissures, the conductivity of the upper crust can be dominated by either the electrolytic conductivity of brine-filled fissures or by the intrinsic conductivity of the rocks. The conductivity of the deeper crust will be dominated by the intrinsic conductivity of the rocks.
T51B-0445 0800h
Controlled Analogue Experiments of the Propagation of Seismic Electromagnetic Signals
Numerous electromagnetic signals at a broad range of frequencies associated with earthquakes have been reported. Some of these signals have been used in the studies of earthquake prediction. However, the correlation between these signals and earthquakes is still controversial. One controversy is the lack of physical nature of the generation and propagation mechanisms. Although one hypothesis considering a certain underground conductive channel was developed to explain selectivity and long distance propagation of seismic electromagnetic signals (SEMS), this explanation highly depends on the existence of the expected underground conductive channel. Thus, it would be necessary to investigate experimentally the propagation of SEMS, till a scientifically credible theory has been made to explain those reported selectivity and long distance propagation. Motivated by the waveguide concept, a scaled geographical model experiment on the propagation of electromagnetic waves in several waveguides was developed. Application of the above analogue experiment to the earthquakes in Greece indicated some aspect of selectivity and long distance propagation may be related to the distribution of surface conductivity. In the current study, several controlled experiments have been done to investigate the following possible influences to the propagation of SEMS: background electromagnetic field, geography, border condition, source (position, intensity, frequency), and conductivity of media. The 1995 M=7.2 Kobe earthquake was chosen as an example in the current study. The results of these controlled experiments indicated that the influence from background field may be neglectable at the current S/N of the analogue experiment. The influence from border condition and source (position and intensity) may be also neglectable as long as the signals can be detected at the current sensitivity in the experiment. However, the propagation pattern of SEMS depends on geographical condition (inhomegeneity of surface conductivity) and source (frequency). The results of the above controlled experiments strengthened the reliability of the previous studies and provided some potential improvements in future analogue experiment.
T51B-0446 0800h
Electric-discharge Luminescence between Frictional Natural Quartz by Pin-on-disk Method: Possible Origin of Seismo-electromagnetic Radiation
To elucidate mechanisms of electromagnetic radiations before and during earthquakes, electric-discharge luminescence around a frictional quartz interface was investigated using a vacuum tribometer with a pin-on-disk arrangement. A pin with a quartz tip slides on a quartz disk under various normal forces and sliding velocities. The disk and the pin were made from a single crystal of Brazilian quartz. The quartz disk was cut normal to c-axis and polished on both sides. The thickness and the radius of the disk were 1 mm and 17.5 mm, respectively. An optical microscope and a charge coupled device (CCD) video camera were used to take luminescence images through the transparent quartz disk. The frictional experiments can be conducted under sliding velocities ranging from 10 mm/s (0.1 rps) to 102 mm/s (1 rps) and normal forces ranging from 50 mN to 150 mN. From the total area of contact points, normal stress can be estimated ranging from 4 MPa to 11 MPa. All experiments were performed under controlled ambient gas pressure of Ar and N$_{2}$ and a room temperature. Based on these experimental conditions, we investigated the dependences of luminescence intensities on normal stresses and gas pressures. Under a constant gas pressure (Ar: 1.2$\times$10$^{4}$ Pa) and a constant sliding velocity (51 mm/s), luminescence intensities per unit area increase with normal stresses. Moreover under a constant sliding velocity (102 mm/s) and a constant normal stress (11MPa), luminescence intensities increase with N$_{2}$ gas pressures up to 1.2$\times$10$^{3}$ Pa and decrease with further increases in N$_{2}$ gas pressures. Our preliminary results indicate that densities of electric charge between a frictional interface increases with increases in normal stresses, and electric-discharge luminescence (plasma luminescence) due to dielectric breakdown of the ambient gas occurs at the interface. The contact electrification (triboelectrification) around frictional quartz interfaces, which causes the electric discharge and the dielectric breakdown of the ambient gas, can generate electromagnetic radiations (Hertz radiations or radiations from electric discharges) or electric-discharge luminescence accompanied with earthquakes.
T51B-0447 0800h
Magnetic Properties of Magnetite and Titanomagnetite Under Pressures 0 to 6 GPa: Implications for Earthquake Prediction
Through the development of new diamond anvil cell technology, we can now measure hysteresis loops and full magnetic vectors of magnetic materials under pressures in excess of 30 GPa. These new techniques are advantageous for investigating the pressure dependence on the magnetic properties of magnetic minerals whose compositions and grain-size spectra are well characterized. Pure multidomain (MD) and single domain (SD) magnetite respond quite differently to stress, with MD grains being much more stress sensitive than SD grains. For the titanomagnetite series, we find that initial susceptibility and saturation moment decrease as a function of increasing pressure and Ti concentration. We define a constant called the median destructive stress, which is the pressure needed to remove one-half of the original (pre-stressed) initial susceptibility, and we show that this value is proportional to the inverse of the magnetostriction constant, consistent with established theory. Thus, by merely knowing the magnetostriction constants of a given magnetic mineral, one should be able to predict its sensitivity to an imposed stress. With this in mind, one can revisit the relevance of piezo-remanent magnetization and stress demagnetization to earthquake prediction, or the build up or relaxation of stress in the crust due to tectonic motion, which has proved elusive. Terrains containing Ti-rich titanomagnetite phases, such as oceanic crust (ophiolites), should be considered the best places to look for changes in the local magnetic field during an earthquake.
T51B-0448 0800h
Anomalous Magnetic Field Pulses, Ground Currents, and the Build-up of Stress prior to the Chi-Chi Earthquake
Before the Sept. 21, 1999 Chi-Chi earthquake in Taiwan and during the period of aftershocks local magnetic field anomalies (up to 200 nT) were recorded at two stations of the Taiwan magnetometer network. The magnetic pulses each lasted for several hours. They arrived in week-long bunches and extend over more than three months. Powerful ground currents are required to generate such strong local magnetic fields, in the order of 10$^{6}$ Amp at peak intensity. The seismic energy released by small earthquakes (earthmurmur) during the weeks before the main shock shows a similar time-dependent evolution, which correlates with the magnetic field anomalies. This suggests that the ground currents are generated when the regional stresses increase as signaled by an increase in the frequency of small earthquakes. We have measured in the laboratory the stress-induced electrical currents generated in igneous rocks (granite and anorthosite). Our experiments show that these rocks exhibit a battery-like behavior, i.e. they produce currents, which flow out of the stressed rock volume into the surrounding unstressed rock. The charge carriers are electronic and positively charged. They are believed to be positive holes (p-holes), i.e. defect electrons in the valence band of the otherwise insulating rocks. The number of outflowing charge carriers is in the order of 106 cm$^{-3}$ of stressed rock. Scaling up to the dimensions of the Chi-Chi event and assuming that the compressed rock volume was 100 x 10 x 50 km$^{3}$ (length of the surface rupture in the N-S direction x thickness x width in the E-W direction) we find that the number of charge carriers activated in such a large "source volume" would suffice to produce outflow currents in the order of 10$^{6}$ Amps over an extended period of time.
T51B-0449 0800h
Reduction Of Geomagnetic Effects (Periods T $<$ 1000 s) From Geomagnetic And Geoelectrical Potential Difference Data
Electromagnetic phenomena preceding large earthquakes have been reported in various frequency ranges and they are considered as candidates for the short-term prediction. ULF electromagnetic phenomena are most promising among them because of the deep skin depth. In order to verify earthquake-related electromagnetic phenomena and clarify the possible physical mechanisms, a network observation has been established in Japan. The observed ULF magnetic and electric potential data are superposition of signals: (1)global signals originated from the external source field associated with the solar-terrestrial interaction like geomagnetic pulsations and their inductive field, which appears simultaneously in scale of hundreds of km, (2) regional (a few tens of km) signals such as artificial noises associated with the leakage current from DC-driven trains, and earthquake-related signals, (3) local (less than few kms) signals around the sensors. The signals associated with the crustal activity are very weak in general, and therefore the sophisticated signal separation is important. As for the ULF geomagnetic data, we have already developed effective methods such as polarization analysis, principal component analysis, and direction fractal analysis. These methods detect signal characteristics. In order to clarify physical mechanisms of earthquake-related ULF signals, time series analysis to identify waveform is required. In this aim, we developed the method for elimination of the most intense external source fields originated from solar-terrestrial interaction. It is interstation transfer function (ISTF) method. The ISTF method is based on the correlation between a site and a quiet remote reference station. Once interstation transfer function is estimated with high accuracy, which is considered to be invariant in time, it is possible to estimate the ideal external source field and their inductive variations at the site. Therefore, the resudials between the observed and estimated variations at the site provide only regional and local variations and earthquake-related phenomena are included. Generally, ISTF approaches were based on the conventional Fourier transform, but we use the wavelet transform due to existence of transient changes. In this paper, the proposed method has been applied to the data observed at the sites in Boso Peninsula, Japan and we use geomagnetic data observed at Kakioka Magnetic Observatory, Japan Meteorological Agency, as the remote reference data. We applied the proposed method to the geomagnetic and geoelectrical potential data to evaluate the elimination of global geomagnetic changes and their inductive fields in the frequency range of 0.001 to 1 Hz. The obtained performance is found to be quite good and changes associated with geomagnetic pulsations are effectively eliminated.
T51B-0450 0800h
Interferometric observation of over-horizon and ionospheric VHF radio waves associated with earthquakes.
Recently it has been found that the perturbations in the atmosphere and ionosphere take place in association with earthquakes (Hayakawa and Molchanov, 2002 Monograph). Fukumoto et al. (2001) have found that the over-horizon VHF waves (FM broadcasting signals) are occasionally observed prior to an earthquake, and their VHF direction finding has indicated that the reception of those over-horizon VHF signal is due to the perturbation in the atmosphere. Additionally Takano et al. (2001) have found that the TV VHF signals in the South-East Asia (like Thailand and China) are often received in Japan in possible association with earthquakes. In order to investigate the mechanism of those VHF anomalous signals, we have developed an interferometric measurement for those VHF signals to determine their direction of arrival (incident (elevation) angle and azmuthal angle (bearing)). We first describe our interferometer system, then show some preliminary observational data, and followed by the future system.
T51B-0451 0800h
Some recent observational results on seismogenic ULF emissions.
It is known that electromagnetic emissions take place in association with earthquakes in a wide frequency range from DC/ULF to VHF. But the most promising frequency range from the standpoint of short-term earthquake prediction is ULF (ultra-low-frequency, f<10Hz), because those ULF emissions are definite to have come from the focal zone. While, the generation mechanisms of higher frequency seismogenic emissions are extremely poorly understood. We show our latest results on seismogenis ULF emissions. The first one is the principal component analysis (PCA) for the ULF emissions associated with the Izu islands earthquake swarm in July 2000. Then, the second will be the fractal (mono-and multi-) analysis for the Guam earthquake. These sophisticated signal processing would be of great importance in elucidating precursory weak seismogenic ULF emissions.
T51B-0452 INVITED 0800h
COMPASS-2 and VULKAN satellite system for the short-term earthquake warning
The beginning of the 21th century was marked by important transition - from discussions on the physical reality of the ionospheric precursors of earthquakes to the practical realization of the dedicated space projects for registration of these precursors from space. Up to now there are 3 space vehicles launched: COMPASS-1, Russia (December 2001), Quakesat, USA (June 2003), and DEMETER, France (June 2004). It was demonstrated that for the real-time monitoring of the short-term precursors in the ionosphere, it is not enough one satellite. That's why the Vulkan project was proposed - the constellation of small satellites on two altitude levels ~ 500 km, and ~ 1000 km. To check some ideas and technological developments the pre-system pilot project COMPASS-2 will be launched in the first half of 2005. the paper presents the physical background of the created satellite constellation, payload selection as a result of analysis of the previous satellite missions connected with the precursors registration, satellite orbit configuration, and the problems of the data assimilation, processing and interpretation.
<a href='http://www.izmiran.rssi.ru/spacegeo/vulcan/' >http://www.izmiran.rssi.ru/spacegeo/vulcan/
T51B-0453 0800h
Full Wave Calculation of the Source Characteristics of Seismogenic Electromagnetic Signals as Observed at LEO Satellite Altitudes
We perform a numerical analysis of the propagation of electromagnetic waves that originate below the Earth's surface and are observed at low Earth orbit (LEO) altitudes, in support of recent missions such as QuakeSat I and Demeter, whose primary objective is the detection and identification of seismogenic electromagnetic signals. For our investigation we subdivide the intervening medium between source and observation into a large number of horizontally stratified, anisotropic slabs and solve the full-wave equations using the matrix method introduced by Nagano et al. [1975]. The effects of the altitude variations of the conducting ground, ionospheric electron density and collision frequency, as well as ion composition are easily included in our model, and we present results as a function of wave frequency and initial wave normal angle for the example case of the Dec. 22 2004, M6.4 San Simeon earthquake.
T51B-0454 0800h
Ionospheric Penetration of ELF/VLF Electromagnetic Waves Radiated From an Earthquake
Theoretical calculations for electromagnetic waves associated with earthquakes have been proposed to analyze the detailed mechanisms and the effects of them. In this study, we compute rigorously the wave intensities in the magnetized ionosphere radiated from an underground current source by using full-wave analysis. We assume that a seismic source is a large electric dipole located underground as the combination of much smaller dipole polarizations created around epicenter. Full-wave analysis has been developed to calculate rigorously the VLF wave propagation in the ionosphere and is extended to analyze the spherical waves radiated from the underground source, which are expanded into a large number of elementary plane waves by using the spherical Bessel function. The effects of the geomagnetic field on the ionospheric wave propagation are considered. The computed results in the frequency range from 10 Hz to 10 kHz show the difference in spatial distributions of the wave intensities due to the whistler-mode propagation. The wave power tends to increase as the frequency decreases, caused by the skin depth effect where lower frequency waves would be less attenuated in the ground medium. In our computation, we see that the magnetic filed is 10$^{-5}$ nT/Hz$^{1/2}$ at the altitude of 200 km in the ionosphere when a 10-kA$\cdot$m current moment is assumed to be created 10 km underground.
T51B-0455 0800h
Preliminary Findings on perturbation of Jet Stream Prior to Earthquakes
The precursors of earthquake include the perturbations in the ionosphere. It seems possible that before the occurrence of an earthquake, there would also be perturbations in the ionosphere. The disturbance of ionosphere ranges from 90km to 2400km. This paper proposes to investigate the jet stream in this lower stratum of the atmosphere. The normal velocity of jet stream is hundreds kilometers per hour By observation, prior to an earthquake takes place, the uniform velocity streamline of a jet stream with height of 9.6km will suddenly disrupt or the anterior of jet stream stay at epicenter for a certain time. The time range of prediction is within 30 days, magnitude scale is M>5.0. There are 3 exact hits within the 21 predicted data ; and 8 samples of partial hit (the predicted area is correct but time is a little bit delayed or scale of earthquake is not correct). However, it is necessary to adjust the magnitude range in the different region. The longer time jet stream stays at the same place, the higher probability of earthquake occurs. This method may serve as a reference for future earthquake forecast research.
<a href='http://home.kimo.com.tw/wu10002002/ http://www.syzygyjob.net/prediction/' >http://home.kimo.com.tw/wu10002002/ http://www.syzygyjob.net/prediction/
T51B-0456 0800h
A Study of Lightning Activities and M$>$=5.0 Earthquakes in Taiwan During 1993-2002
Lightning activities near the fault zone significantly enhanced 2-7 days prior to the Chi-Chi earthquake (Mw7.7, 1747 UT, 20 September 1999). A statistical investigation of lightning activities 15 days before and after 279 M$>$=5.0 earthquake days occurred in Taiwan during 1993-2002 are carried out. We isolate lightning occurrences within 50km x 50km area of each epicenter 15 days before and after the earthquakes and stack for the overall 279 earthquakes, the 206 sea earthquakes, and the 73 land earthquakes. Results shows for the overall, sea, and land earthquakes that the ratios of the stack sum of the 1-15 days before to the after are 56%/44%, 50%/50%, and 65%/35%, respectively. We further examine lightning activities associated with the overall 35, the 26 sea earthquakes, and the 9 land M$>$=6.0 earthquakes during the same period. The ratios of the overall, the sea and the land earthquakes are 59%/41%, 48%/52%, and 77%/23%, respectively. The larger values of the ratios indicate that lightning activities before the land earthquakes are enhanced.
T51B-0457 0800h
The search for Infrared radiation prior to major earthquakes
This work describes our search for a relationship between tectonic stresses and electro-chemical and thermodynamic processes in the Earth and increases in mid-IR flux as part of a possible ensemble of electromagnetic (EM) phenomena that may be related to earthquake activity. Recent analysis of continuous ongoing long- wavelength Earth radiation (OLR) indicates significant and anomalous variability prior to some earthquakes. The cause of these anomalies is not well understood but could be the result of a triggering by an interaction between the lithosphere-hydrosphere and atmospheric related to changes in the near surface electrical field and gas composition prior to the earthquake. The OLR anomaly covers large areas surrounding the main epicenter. We have use the NOAA IR data to differentiate between the global and seasonal variability and these transient local anomalies. Indeed, on the basis of a temporal and spatial distribution analysis, an anomaly pattern is found to occur several days prior some major earthquakes. The significance of these observations was explored using data sets of some recent worldwide events.
T51B-0458 0800h
ULF Geomagnetic Anomaly Associated with Large Earthquakes
Despite its extreme importance and years of effort, practical short-term earthquake prediction still remains to be achieved in future. However, earthquake-related electromagnetic phenomena are recently considered as a promising candidate for short-term earthquake prediction. There have been accumulated a lot of evidences of precursory signatures in a wide frequency range (DC-VHF). The ULF geomagnetic change is one of the most promising phenomena. It is important to confirm the reality of the ULF phenomena associated with EQ and also the reliability of possible short-term EQ prediction using them. This report is summary of the ULF research in collaboration with RIKEN-IFREQ, UEC-NASDA group, and Chiba University.
T51B-0459 0800h
Association of SLHF and Ionospheric Anomalies with the Coastal Earthquakes of Japan
Earthquakes are frequent natural hazards that pose a serious threat to our society. Numerous earthquakes occur every year throughout the globe, which may cause little to severe damage depending on their magnitude, depth, location, and the level of preparedness of the inhabitants of the affected region. In the recent years, numerous types of precursory signals of impending earthquakes have been observed and studied. VLF/LF subionospheric radio wave monitoring is being widely carried out in Japan for analysis of earthquake preparatory process, and several anomalies have been observed prior to large earthquakes of Japan using ground based and satellite measurements. Similarly SLHF has recently been introduced as a possible precursor, and in the case of coastal earthquakes, the consistent occurrence of anomalous SLHF peaks few days prior to the main earthquake event has been observed. In the present work we have compared ionospheric and SLHF anomalies of various Japanese coastal earthquakes. In the case of the Tokachi earthquake, SLHF anomalies in NCEP/NCAR data, and ionospheric anomalies in data from the HOK station in Japan and KAM station in Kamchatka, Russia, exhibit a very similar behavior. In particular the Japanese station show two large anomalous signals 5 days prior and 7 days after the main earthquake event, which show complementary nature with the SLHF anomaly for the same region. The SLHF and ionospheric anomalies associated with coastal earthquakes of Japan show a close relation.