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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 2028 Earthquake precursors detected through the analysis of mutual interactions of hydrogeochemical signals Mrs. Laura Castellana Department of Biomedical Sciences University of Foggia IASPEI Pier Francesco Biagi Many studies showed that changes in hydrogeochemical time series can be related to earthquakes. In particular, the detection of seismic precursors is traditionally carried out associating the spectral content of the time series analyzed to the occurrence of seismic events. The limit of this approach is twofold: first it is based on a posteriori signal analysis, second each groundwater parameter is analysed singularly and their mutual correlations are not investigated. Here correlations are meant both as interactions among hydrogeochemical parameters and as interactions between these parameters and the occurrence of seismic precursors. To overcome these drawbacks, we use a classifier that, appropriately trained on a finite and limited number of examples (training set), learns to predict the occurrence of seismic events in new observations of hydrogeochemical data. The training set is composed of l couple of examples {(xi,yi)}, i=1,...,l , where the vector xi is the temporal window, large m, of the signal and yi is a label identifying the signal pattern, i.e. yi =0 or yi =1 or yi =2 if xi is a noseismic signal or precursor signal or co-post seismic signal, respectively. Under this perspective, the problem of detecting hydrogeochemical precursors becomes the problem to predict the correct output yj relative to never seen before input pattern xj. The prediction accuracy and the number of false positives provide a quantitative measure of the capability of the multivariate predictor in discriminating noseismic/ precursor/ co-post seismic signal. Furthermore, these quantities provide also an estimate of correlations between hydrogeochemical data and earthquakes, because the higher prediction accuracy, the better correlations among these quantities. The dataset used in this study is composed of thirteen geochemical time series collected in Kamchatka (Russia) peninsula, since 1977. The predictor we worked with is K Nearest Neighbour classifier. In order to compute the prediction accuracy, we use the Leave-K-Out-Cross-Validation (LKOCV) procedure, a statistically well founded method for estimating the accuracy of predictors by using a finite number of observations. We applied K Nearest Neighbour classifier to study the correlations among ions (Na+, Cl-, Ca++, HCO3 and H3BO3), among parameters (pH, Q and T) and finally among gases (N2, CO2, CH4, O2 and Ar) in order to establish if their interactions improve the prediction accuracy of seismic precursors. The results show the model order is proportional to the prediction accuracy. This is a proof that information collected some months before the event under analysis are necessary to improve the classification accuracy. In particular, we obtained a prediction accuracy of 78% in a temporal window of size m=80. Keywords: precursors, knn classifier, prediction
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 2029 Changes of the electromagnetic parameters used as possible seismic premonitory signals Dr. Dumitru Stanica Electromagnetism and Lithosphere Dynamics Institute of Geodynamics of the Romanian Academy IAGA Maria Stanica, Nicoleta Vladimirescu Identification of electromagnetic (EM) precursory parameters related to the seismic activity is still under scientific debate and requires new reliable information about their possible interrelation with changes of electrical conductivity occurred prior to the geodynamic process. The paper emphasizes the anomalous behaviour of the EM parameters as possible premonitory signals under the circumstances of the specific geotectonic characteristics of the Vrancea zones intermediate depth seismicity. In this respect, measurements of geomagnetic field have been performed since 2001 year and recording network has consisted of two high sensitive geomagnetic systems placed at the Surlari National Geophysical Observatory and Provita de Sus Geodynamic Observatory. Every recording system consists of data logger with 6 channels and A/D converter of 24 bits resolution, three-axis magnetic field sensor (frequency range: DC- 1kHz) and a laptop for real time data storage and processing. One of the horizontal components of the three-axis magnetic sensor has always been orientated perpendicular to the geological strike in order to record its time variation. It is well known that a large-scale regional conductivity anomaly causes a regional amplification of the vertical magnetic component Bz as well as spatial changes of the horizontal magnetic component perpendicular to strike (Bper.). Subsequently, a specific approach regarding the electromagnetic precursory parameters (Bzn=Bz/Bper. and ρn=ρ║/ρz, where ρ║ is resistivity parallel to strike and ρz is vertical resistivity), selected according to the temporal invariability criterion for a 2D geoelectric structure in non-seismic condition, taking into consideration their daily mean distribution versus intermediate depth seismic events recorded simultaneously, was elaborated. These changes of electrical conductivity inside of the Vrancea seismogenic slab and its surroundings, before the earthquakes to occur, as a sequence of the lithospheric conductivity changes produced maybe by the dehydration of the rocks associated with rupturing processes and fluid migration through faulting systems are reflected by the anomalous behaviour of the Bzn and ρn parameters and, finally, several conclusions concerning mutual interrelation within a span of 6 years interval are inferred. We claim that this specific methodology together with more complete approach of EM phenomena can improve the seismic hazard assessment. Keywords: electromagnetic, precursory parameters, seismicity
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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy<br />
(S) - <strong>IASPEI</strong> - International Association of Seismology and Physics of the Earth's<br />
Interior<br />
JSS009 Oral Presentation 2029<br />
Changes of the electromagnetic parameters used as possible seismic<br />
premonitory signals<br />
Dr. Dumitru Stanica<br />
Electromagnetism and Lithosphere Dynamics Institute of Geodynamics of the Romanian<br />
Academy IAGA<br />
Maria Stanica, Nicoleta Vladimirescu<br />
Identification of electromagnetic (EM) precursory parameters related to the seismic activity is still under<br />
scientific debate and requires new reliable information about their possible interrelation with changes of<br />
electrical conductivity occurred prior to the geodynamic process. The paper emphasizes the anomalous<br />
behaviour of the EM parameters as possible premonitory signals under the circumstances of the specific<br />
geotectonic characteristics of the Vrancea zones intermediate depth seismicity. In this respect,<br />
measurements of geomagnetic field have been performed since 2001 year and recording network has<br />
consisted of two high sensitive geomagnetic systems placed at the Surlari National Geophysical<br />
Observatory and Provita de Sus Geodynamic Observatory. Every recording system consists of data<br />
logger with 6 channels and A/D converter of 24 bits resolution, three-axis magnetic field sensor<br />
(frequency range: DC- 1kHz) and a laptop for real time data storage and processing. One of the<br />
horizontal components of the three-axis magnetic sensor has always been orientated perpendicular to<br />
the geological strike in order to record its time variation. It is well known that a large-scale regional<br />
conductivity anomaly causes a regional amplification of the vertical magnetic component Bz as well as<br />
spatial changes of the horizontal magnetic component perpendicular to strike (Bper.). Subsequently, a<br />
specific approach regarding the electromagnetic precursory parameters (Bzn=Bz/Bper. and ρn=ρ║/ρz,<br />
where ρ║ is resistivity parallel to strike and ρz is vertical resistivity), selected according to the temporal<br />
invariability criterion for a 2D geoelectric structure in non-seismic condition, taking into consideration<br />
their daily mean distribution versus intermediate depth seismic events recorded simultaneously, was<br />
elaborated. These changes of electrical conductivity inside of the Vrancea seismogenic slab and its<br />
surroundings, before the earthquakes to occur, as a sequence of the lithospheric conductivity changes<br />
produced maybe by the dehydration of the rocks associated with rupturing processes and fluid<br />
migration through faulting systems are reflected by the anomalous behaviour of the Bzn and ρn<br />
parameters and, finally, several conclusions concerning mutual interrelation within a span of 6 years<br />
interval are inferred. We claim that this specific methodology together with more complete approach of<br />
EM phenomena can improve the seismic hazard assessment.<br />
Keywords: electromagnetic, precursory parameters, seismicity