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Electronic Resource

Aquifer-induced Seismicity in the Central Apennines (Italy) (1998)

Bella, F. ; Biagi, P. F. ; Caputo, M. ; [et al.]

Springer

Pure and applied geophysics 153 (1998), S. 179-194

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ISSN: 1420-9136

Keywords: Key words: Induced seismicity, flow rate, water level, preseismic anomalies, aquifer.

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract —The Gran Sasso chain (Central Apennines, Italy) contains one of the largest aquifers of Central Italy. From 1970–1986 the massif was tunnelled through in order to build up a highway and an international underground laboratory for nuclear physics research. These works have strongly modified the hydrogeological situation of the chain, as shown by the decrease in flow rate that occurred in many springs located at the border of the carbonatic structure, along the boundary between the permeable limestone of the massif and the surrounding aquicludes. The analysis of the seismicity (M≥ 3.0) that occurred in the Gran Sasso area from 1956 to 1995 suggests that after the tunnelling works both the number of earthquakes has increased and epicenters have migrated, gathering at the northwestern border zone. The foremost events which occurred in this zone in recent years took place on May 5, 1992 (M = 3.1), August 25, 1992 (M = 3.9) and March 13, 1994 (M = 3.5). The flow rate data of four springs and water level data of an underground karst pool located at the border of the carbonatic structure of the massif show clear anomalies before the occurrence of the quoted earthquakes. Regardless, these anomalies can be explained by the rapid melting of the thick mantle of snow on the Gran Sasso chain, due to sudden increases of mean temperatures. In this paper we present and discuss the possibility that the quoted earthquakes are induced by the irregular variations of the Gran Sasso aquifer, evidenced by the quoted anomalies in the flow rate and water level.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s000240050191

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2

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Groundwater Ion Content Precursors of Strong Earthquakes in Kamchatka (Russia) (2000)

Biagi, P. F. ; Ermini, A. ; Kingsley, S. P. ; [et al.]

Springer

Pure and applied geophysics 157 (2000), S. 1359-1377

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ISSN: 1420-9136

Keywords: Key Words: Precursors, earthquakes, groundwater, ions, Kamchatka.

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: 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.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/PL00001123

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3

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Automatic equipment to monitor groundwater radon (1993)

Bella, F. ; Bella, R. ; Biagi, P. F. ; [et al.]

Springer

Pure and applied geophysics 141 (1993), S. 125-137

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ISSN: 1420-9136

Keywords: Automatic equipment ; groundwater radon ; environment ; earthquake precursors

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Prototype instrumentation, able to automatically measure groundwater radon content variations, is presented. The equipment is made of stainless steel and has spherical valves with automatic and pneumatic control. The deemanation of the gases from the water is obtained by evacuating a suitable expansion chamber. The instrumentation can make discrete sampling ranging from 1 per hour to 1 per 99 hours. The equipment was tested in the laboratory: the efficiency was measured by means of a266Ra solution. A mean value of (0.65±0.07) count/s/Bq was obtained. A calibration test was carried out by comparing countings from the automatic equipment with those obtained by the standard laboratory cell. Results of an operational check over a period of approximately one year indicate that variations in radon at the calibration site are attributable more to meteorological than to tectonic causes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00876239

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4

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Possible creep-related tilt precursors obtained in the Central Apennines (Italy) and in the Southern Caucasus (Georgia) (1995)

Bella, F. ; Biagi, P. F. ; Caputo, M. ; [et al.]

Springer

Pure and applied geophysics 144 (1995), S. 277-300

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ISSN: 1420-9136

Keywords: Fault creep ; ground tilt ; earthquake precursors

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00878635

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5

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Transmission and reflection of Rayleigh waves at a thin low velocity vertical layer: A laboratory and theoretical study (1990)

Biagi, P. F. ; Gegechkory, T. S. ; Its, E. N. ; [et al.]

Springer

Pure and applied geophysics 133 (1990), S. 317-327

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ISSN: 1420-9136

Keywords: Low velocity ; vertical layer ; Rayleigh waves

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract A three-dimensional ultrasonic modelling was used to study the Rayleigh waves reflected from a thin low velocity vertical layer and those transmitted through the same zone. The reflection and transmission coefficients of the Rayleigh waves have been calculated by an approximate method based on the Green function technique. Nonrigid contact boundary conditions were used for the low velocity layer modelling. A rather good correspondence between the theoretical and experimental absolute values of the reflection and the transmission coefficients was obtained. Some discrepancies between experimental and theoretical results, in particular with regard to phase shifts, may be explained by a certain inadequacy of the theoretical model to the low velocity layer investigated by the ultrasonic modelling.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00877166

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6

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Hydrogeochemical Precursors in Kamchatka (Russia) Related to the Strongest Earthquakes in 1988–1997 (2000)

Biagi, P. F. ; Ermini, A. ; Cozzi, E. ; [et al.]

Springer

Natural hazards 21 (2000), S. 263-276

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ISSN: 1573-0840

Keywords: earthquakes ; precursors ; hydrogeochemicals ; Kamchatka

Source: Springer Online Journal Archives 1860-2000

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences

Notes: 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 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

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008178104003

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