Retrospective analysis for detecting seismic precursors in groundwater argon content

We examined the groundwater Argon content data sampled from 1988 to 2001 at two wells in Kamchatka (Russia) and anomalous increases appeared clearly during June-July&nbsp;1996. On 21&nbsp;June, a shallow (1km) earthquake with <i>M</i>=7.1 occurred at a distance less than 250km from the wells and so the previous increases could be related to this earthquake and, in particular, could be considered premonitory anomalies. In order to support this raw interpretation, we analysed the data collected in details. At first we smoothed out the high frequency fluctuations arising from the errors in a single measurement. Next we considered the known external effects on the water of a well that are the slow tectonic re-adjustment processes, the meteorology and the gravity tides and we separated these effects applying band-pass filters to the Argon content raw trends. Then we identified the largest fluctuations in these trends applying the 3 σ criterion and we found three anomalies in a case and two anomalies in other case. Comparing the time occurrence of the anomalies at the two wells we found out that a coincidence exists only in the case of the premonitory anomalies we are studying. The simultaneous appearance of well definite anomalies in the residual trends of the same parameter at two different sites supports their meaning and the possibility that they are related to some large scale effect, as the occurrence of a strong earthquake. But, other earthquakes similar to the June&nbsp;1996 event took place during the Argon content measurements time and no anomaly appeared in this content. In the past, some of the authors of this paper studied the Helium content data collected in three natural springs of the Caucasus during seven years. A very similar result, that is the simultaneous appearance of clear premonitory anomalies only on the occasion of a strong (<i>M</i>=7.0) but shallow (2–4km) earthquake, was obtained. The correspondence with the case of the Caucasus validates the interpretation of the Kamchatkian anomalies as precursors

Cross-Correlation Earthquake Precursors in the Hydrogeochemical and Geoacoustic Signals for the Kamchatka Peninsula

We propose a new type of earthquake precursor based on the analysis of correlation dynamics between geophysical signals of different nature. The precursor is found using a two-parameter cross-correlation function introduced within the framework of flicker-noise spectroscopy, a general statistical physics approach to the analysis of time series. We consider an example of cross-correlation analysis for water salinity time series, an integral characteristic of the chemical composition of groundwater, and geoacoustic emissions recorded at the G-1 borehole on the Kamchatka peninsula in the time frame from 2001 to 2003, which is characterized by a sequence of three groups of significant seismic events. We found that cross-correlation precursors took place 27, 31, and 35 days ahead of the strongest earthquakes for each group of seismic events, respectively. At the same time, precursory anomalies in the signals themselves were observed only in the geoacoustic emissions for one group of earthquakes.Comment: 21 pages, 5 figures, 1 table; to be published in "Acta Geophysica". arXiv admin note: substantial text overlap with arXiv:1101.147

Hydrogeochemical precursors of strong earthquakes in Kamchatka: further analysis

International audienceFor many years, ion and gas content data have been collected from the groundwater of three deep wells in the southern area of the Kamchatka peninsula, Russia. In the last ten years, five earthquakes with M > 6.5 have occurred within 250 km of the wells. In a previous study, we investigated the possibility that the hydrogeochemical time series contained precursors. The technique used was to assume that each signal with an amplitude of three times the standard deviation is an irregularity and we then defined anomalies as irregularities occurring simultaneously in the data for more than one parameter at each well. Using this method, we identified 11 anomalies with 8 of them being possible successes and 3 being failures as earthquake precursors. Precursors were obtained for all five earthquakes that we considered. In this paper, we allow for the cross-correlation found between the gas data sets and in some cases, between the ion data sets. No cross-correlation has been found between gas and ion content data. Any correlation undermines the idea that an anomaly might be identified from irregularities appearing simultaneously on different parameters at each site. To refine the technique, we re-examine the hydrogeochemical data and define as anomalies those irregularities occurring simultaneously only in the data of two or more uncorrelated parameters. We then restricted the analysis to the cases of just the gas content data and the ion content data. In the first case, we found 6 successes and 2 failures, and in the second case, we found only 3 successes. In the first case, the precursors appear only for three of the five earthquakes we considered, and in the second case, only for two, but these are the earthquakes nearest to the wells. Interestingly, it shows that when a strict set of rules for defining an anomaly is used, the method produces only successes and when less restrictive rules are used, earthquakes further from the well are implicated, but at the cost of false alarms being introduced

Co-postseismic hydrogeochemical anomalies in a volcanic environment

For many years flow-rate, temperature, ions and gases content data have been collected from a natural spring located in the Koryakskiy volcano area (Kamchatka, Russia). We have investigated the correlations between the hydrogeochemical data and the areal seismicity represented by the ks values (ks&nbsp; is a function of magnitude and hypocentral distance) of the earthquakes. At first we smoothed the raw hydrogeochemical data using a semi-triangle weight function. Then we compared the trends of each smoothed hydrogeochemical parameter with the ks&nbsp; trend using a running cross-correlation function with a maximum lag of ± 30 days and the main result was that, sometimes, we found 0.7–0.4 cross-correlation coefficients with no lag for flow rate and with + (10 – 15) days lags for some ion and gas contents. The correlation is positive, i.e. flow rate and ion and gas contents increase when ks&nbsp; increases. This phenomenology could be explained by an underground water pumping produced by some earthquake. We advance the hypothesis that this pumping could be the response of the viscoelastic underground medium of the Koryakskiy volcano to seismic waves. So, sometimes, the supply of elastic energy of the earthquakes may provide the trigger to a catastrophic nucleation of bubbles of this material producing a new melt with a lower density which will tend to expand and cause a pressure increase. This pressure produces a more intensive circulation of underground water and an anomalous increase of the flow rate and subsequently anomalous increases in groundwater ions and gases content

Hydrogeochemical anomalies on the occasion of the M=7.1 earthquake occurred in Kamchatka (Russia) in March 1992

The Kamchatka peninsula, located in the far east of Russia, is a geologically active margin where the Pacific plate subducts beneath the North American and Eurasia plates. This area is characterised by frequent and strong seismic activity and epicen- tres are generally distributed offshore along the eastern coast of the peninsula. The energy released by the earthquakes occurring from January 1977 to December 2004 in a circle of a radius of 350 km centred on the capital city Petropavlosk, reveals an increase in the peak energy release in the period 1992-1998. This increase is related to the occurrence of seven earthquakes with magnitudes greater than 6.5 and contrasts with the previous and successive periods when the seismicity has been more moder- ate. The first of the seven earthquakes happened on March 2, 1992 with M = 7.1. For many years, hydrogeochemical data have been collected with a mean sampling fre- quency of three days in the form of the most common ions and gases in the water of six deep wells and two natural springs in the south area of the Kamchatka peninsula, where the capital city Petropavlovsk is located. The data collected were analysed and differences in the trend and in the spectral content of some hydrogeochemical param- eter were pointed out before and after the occurrence of the 1992 earthquake, indi- cating clear (co)-post seismic effects. Then an evident increase in the CO 2 , CH 4 and H 2 content was revealed, practically at each measurement site, during the two-three years preceding the earthquake, so that long term precursors can be claimed. Finally, in some hydrogeochemical parameter and in some site, anomalies have been revealed some month before the 1992 earthquake as middle term precursors. Such anomalies were observed also on the occasion of the January 1996 earthquake (M = 6.9). The 1992 and 1996 earthquakes, among the seven events previously mentioned, happened nearest (90-120 km) to the measurement sites

Hydrogeochemical variations related to seismic and volcanic activity in Kamchatka (Russia)

Starting from 1992, hydrogeochemical data have been collected with a mean sampling frequency of three days in the form of the pH value and of the most common ions and gases in the groundwater of a deep well located in the capital city Petropavlovsk of Kamchatka (Russia). On January 1, 1996 the Karymsky volcano, located 100 km far from the well in north-northeaster direction, started a strong eruption. Simultaneously a large (M = 6.9) earthquake occurred in the Karymsky area. On December 5, 1997 a very large (M = 7.7) earthquake occurred offshore, 350 km far from the well, in north- easter direction. The raw trends of the hydrogeochemical parameters at the well reveal clear variations occurred for both of the previous events. In the first case, the variations are defined by a clear premonitory phase; in the second one they are post seismic vari- ations and some permanent disturbance in the chemistry of the water appears. During the measurements time other large (M=7.0-7.3) earthquakes occurred at distances less than 250 km from the previous well in south and in east direction. On these occa- sions none evident variation appears in the previous trends. The phenomenology we pointed out reveals a strict structural connection between the Petropavlovsk area and the north-northeaster zone. At the same time it confirms that the appearance of precursors in hydrogeochemical parameters can be anisotropic in space. According to our opinion, this anisotropy could be valid also for other different parameters used in the research on earthquake precursors

Hydrogeochemical variations related to seismic and volcanic activity in Kamchatka (Russia)

Starting from 1992, hydrogeochemical data have been collected with a mean sampling frequency of three days in the form of the pH value and of the most common ions and gases in the groundwater of a deep well located in the capital city Petropavlovsk of Kamchatka (Russia). On January 1, 1996 the Karymsky volcano, located 100 km far from the well in north-northeaster direction, started a strong eruption. Simultaneously a large (M = 6.9) earthquake occurred in the Karymsky area. On December 5, 1997 a very large (M = 7.7) earthquake occurred offshore, 350 km far from the well, in north- easter direction. The raw trends of the hydrogeochemical parameters at the well reveal clear variations occurred for both of the previous events. In the first case, the variations are defined by a clear premonitory phase; in the second one they are post seismic vari- ations and some permanent disturbance in the chemistry of the water appears. During the measurements time other large (M=7.0-7.3) earthquakes occurred at distances less than 250 km from the previous well in south and in east direction. On these occa- sions none evident variation appears in the previous trends. The phenomenology we pointed out reveals a strict structural connection between the Petropavlovsk area and the north-northeaster zone. At the same time it confirms that the appearance of precursors in hydrogeochemical parameters can be anisotropic in space. According to our opinion, this anisotropy could be valid also for other different parameters used in the research on earthquake precursors

Co-postseismic Hydrogeochemical Anomalies in a Volcanic Environement

For many years flow-rate, temperature, ions and gases content data have been collected from a natural spring located in the Koryakskiy volcano area (Kamchatka, Russia). We have investigated the correlations between the hydrogeochemical data and the areal seismicity represented by the ks values (ks is a function of magnitude and hypocentral distance) of the earthquakes. At first we smoothed the raw hydrogeochemical data using a semi-triangle weight function. Then we compared the trends of each smoothed hydrogeochemical parameter with the ks trend using a running cross-correlation function with a maximum lag of ±30 days and the main result was that, sometimes, we found 0.7-0.4 cross-correlation coefficients with no lag for flow rate and with +(10 - 15) days lags for some ion and gas contents. The correlation is positive, i.e. flow rate and ion and gas contents increase when ks increases. This phenomenology could be explained by an underground water pumping produced by some earthquake. We advance the hypothesis that this pumping could be the response of the viscoelastic underground medium of the Koryakskiy volcano to seismic waves. So, sometimes, the supply of elastic energy of the earthquakes may provide the trigger to a catastrophic nucleation of bubbles of this material producing a new melt with a lower density which will tend to expand and cause a pressure increase. This pressure produces a more intensive circulation of underground water and an anomalous increase of the flow rate and subsequently anomalous increases in groundwater ions and gases content

Co-postseismic hydrogeochemical anomalies in a volcanic environment

International audienceFor many years flow-rate, temperature, ions and gases content data have been collected from a natural spring located in the Koryakskiy volcano area (Kamchatka, Russia). We have investigated the correlations between the hydrogeochemical data and the areal seismicity represented by the ks values (ks is a function of magnitude and hypocentral distance) of the earthquakes. At first we smoothed the raw hydrogeochemical data using a semi-triangle weight function. Then we compared the trends of each smoothed hydrogeochemical parameter with the ks trend using a running cross-correlation function with a maximum lag of ± 30 days and the main result was that, sometimes, we found 0.7?0.4 cross-correlation coefficients with no lag for flow rate and with + (10 ? 15) days lags for some ion and gas contents. The correlation is positive, i.e. flow rate and ion and gas contents increase when ks increases. This phenomenology could be explained by an underground water pumping produced by some earthquake. We advance the hypothesis that this pumping could be the response of the viscoelastic underground medium of the Koryakskiy volcano to seismic waves. So, sometimes, the supply of elastic energy of the earthquakes may provide the trigger to a catastrophic nucleation of bubbles of this material producing a new melt with a lower density which will tend to expand and cause a pressure increase. This pressure produces a more intensive circulation of underground water and an anomalous increase of the flow rate and subsequently anomalous increases in groundwater ions and gases content