Y. M. Khatkevich

Hydrogeochemical anomalies in Kamchatka (Russia)

Abstract Data concerning discharge, melted iones and gases from underground waters obtained in Kamchatka during the last ten years are presented. Some hydrogeochemical parameters from a volcanic site reveal clear coseismic and postseismic anomalies on the occasion of five earthquakes with magnitude M > 6.5 that occurred at distances closer than 250 km from the measurement site. Hydrogeochemical parameters from a tectonic site show anomalies on the occasion of three of the above earthquakes. Such earthquakes are characterized by the highest values of the deformation parameter ϵ and the corresponding anomalies are preseismic ones, starting from 1 to 4 months prior to the earthquake. Also, some hydrogeochemical parameters from another tectonic site show clear preseismic anomalies on the occasion of just one of these earthquakes. This last one is located inland while the epicentres of the other earthquakes are well offshore. Models able to explain the phenomenologies we described are proposed.

Hydrogeochemical precursors in Kamchatka (Russia) related to the strongest earthquakes in 1988-1997

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 (magnitudes up to 8.5) and epicentres are generally distributed offshore along the eastern coast of the peninsula. For many years, hydrogeochemicals have been collected with a mean sampling frequency of three days in the form of the flow rate and the most common ions and gases in the groundwater of three deep wells in the southern area of the Kamchatka peninsula, where the capital city Petropavlovsk is located. Beginning in 1988, five earthquakes with M > 6.5 occurred in this area. These earthquakes were powerful enough to be considered as potential precursor sources in the sense that the stresses and strains building up before them might be expected to cause precursory activity. In order to reveal any possible precursors of these earthquakes, we analysed the hydrogeochemical data collected. We considered any signal having an amplitude three times the standard deviation to be an irregularity and we defined as an anomaly the existence of an irregularity occurring simultaneously in more than one parameter at each well. Then, on the basis of the worldwide past results and the time recurrence of the quoted earthquakes, we chose 158 days as the maximum temporal window between a possible anomaly and the subsequent earthquake. We identified some premonitory anomalies in hydrogeochemical parameters at different wells. On the basis of these results some earthquake forecasting criteria in southern Kamchatka may be tentatively formulated

Hydrogeochemical precursors of strong earthquakes: a realistic possibility in Kamchatka

Abstract The Kamchatka peninsula, located in the far East of Russia, is characterised by frequent and strong seismic activity (magnitudes up to 8.6). For many years, samples for hydrogeochemical analyses have been collected with a mean sampling frequency of three days in the form of the pH values and of the most common ions and gases in the groundwater of some deep wells and springs in the south area of the Kamchatka peninsula, where the capital city Petropavlovsk is located. In the last ten years, five earthquakes with M>6.5 have occurred at distances of less than 250 km from the measurement sites. In order to reveal any possible precursors of these earthquakes, the hydrogeochemical data collected from three wells have been analysed. We have identified 12 anomalies with 8 of them being possible successes and 4 failures as earthquake precursors and we have obtained a probability of 67% that any given hydrogeochemical anomaly is an earthquake precursor. One of the results obtained indicates that the possibility of observing precursors in the hydrogeochemical parameters of a well seems to be related to the location of an earthquake with respect to the well. Recently, this behaviour was confirmed when we observed a clear co-post seismic effect in only one well after an earthquake on December 5, 1997, which was about 400 km distant and very strong (M=7.7).

Difficulties with interpreting changes in groundwater gas content as earthquake precursors in Kamchatka, Russia

The Kamchatka peninsula, located in the far east of Russia, is a geologicallyactive margin where the Pacific plate subducts beneath the North Americanand Eurasia plates. This area is characterised by frequent and strong seismicactivity (with magnitudes of up to 8.6), with epicentres generallydistributed offshore along the eastern coast of the peninsula. Starting in1977, hydrogeochemical data have been collected with a mean samplingfrequency of three days in wells and springs located in the southern area ofthe Kamchatka peninsula. In order to reveal possible earthquake precursors,the groundwater gas content data collected in the last ten years at fivewells, were statistically analysed. Each signal exceeding a 3σthreshold was considered to be an irregularity and two different methodsof defining an anomaly were assumed. In the first, an anomaly was declaredwhen an irregularity occurred simultaneously on more than one gas contentat each well. In the second method, an anomaly was declared when anirregularity occurred simultaneously on a given type of gas at more thanone well. As a mechanism for associating an anomaly with an earthquake,the earthquakes that occurred with magnitudes greater than 6.5 and withina distance of 250 km from each well, were selected. Using this frameworkboth successes and failures were identified. It is shown that on the basis ofthis statistical analysis, there is a great probability that the successes revealedare not precursors but random coincidences.

Groundwater ion content precursors of strong earthquakes in Kamchatka (Russia)

Abstract—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 (magnitudes reaching 8.6) and epicentres are generally distributed offshore along the eastern coast of the peninsula. For many years, hydrogeochemicals have been sampled with a mean interval of three days to measure the most common ions in the groundwater of five deep wells in the southern area of the Kamchatka peninsula. In the last decade, five earthquakes with M > 6.5 have occurred at distances less than 250 km from these wells. These earthquakes were powerful enough for them to be considered as potential originators of precursors. In order to reveal possible precursors of these earthquakes, we analysed the groundwater ion contents. The quasi-periodic annual variation was filtered out, together with other slow trends, and then we smoothed out the high frequency fluctuations that arise from errors in a single measurement. When examining the data, we labelled each signal with an amplitude greater than three times the standard deviation as an irregularity and we made a first attempt at defining an anomaly as an irregularity occurring simultaneously in more than one parameter at each well. In a second definition we used the existence of an irregularity occurring simultaneously in each ion at more than one well. Then, on the basis of past results worldwide and the time interval between the earthquakes observed, we chose 158 days as the maximum temporal window between a possible anomaly and the subsequent earthquake. With the first anomaly definition we identified 6 anomalies with 4 possible successes and 2 failures. For the five earthquakes considered capable of producing precursors we obtained precursors in three cases. With the second anomaly definition we identified 10 anomalies with 7 possible successes and 3 failures and we obtained precursors in four of the five earthquakes. A schematic model explaining aspects of the complex relationship linking earthquakes and ion content anomalies is also presented.

Possible precursors in groundwater ions and gases content in Kamchatka (Russia)

Abstract For many years, hydrogeochemicals have been collected with a mean sampling frequency of three days in the form of the most common ions and gases in the groundwater of five deep wells in the Southern area of the Kamchatka peninsula. In the last decade, five earthquakes with M > 6.5 occurred at distances less than 250 km from these wells. In order to reveal possible precursors of these earthquakes we analysed the hydrogeochemicals collected. The quasi-periodic annual variation was filtered out, together with other slow trends, and then we smoothed out the high frequency fluctuations that arise from the errors in a single measurement. When examining the filtered and smoothed data, we labelled each signal with an amplitude greater than three times the standard deviation as an irregularity and we made a first attempt at defining an anomaly as an irregularity which occurs simultaneously in more than one type of ion or gas at each well. In a second definition we used the existence of an irregularity occurring simultaneously in each type of ion or gas at more than one well. Then we chose the minimum time interval between two successive earthquakes as the maximum temporal window between a possible anomaly and the subsequent earthquake. Concerning the ions content, we identified a total of 16 anomalies with 11 successes and 5 failures; for the gases content we identified a total of 25 anomalies with 9 successes and 16 failures. On the basis of the criteria chosen we find the possibility that the successes of ion contents as earthquake precursors is high; but in contrast there is a only small possibility that the successes in gases content are precursors.