Analisi statistica della correlazione tra livello dell'acqua di invasi idrici e sismicita' indotta

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1 Analisi statistica della correlazione tra livello dell'acqua di invasi idrici e sismicita' indotta Luciano Telesca Institute of Methodologies for Environmental Analysis National Research Council, Italy luciano.telesca@imaa.cnr.it

2 Case studies 1. Koyna-Warna (India) 2. Açu (Brazil) 3. Aswan (Egypt) 4. Enguri (Georgia)

3 1. Koyna-Warna (India) Dam is 13 m high Previously a low-sesmicity area Impounding of water began in 1962 Reports of local EQs increased dramatically Seismograms showed foci concentrated at shallow depths under Shivajisagar Lake M 6.5 EQ close to the Dam on Dec. 1, 1967 (Gupta et al., BSSA, 198)

4 N magnitude W (m) 1. Koyna-Warna (India) a b c days since January 1, days since January 1, 21 Observation period: Mc =2.2 B-value=1.3 Telesca, BSSA, , 21

5 cross-correlation between n and w 1. Koyna-Warna (India) % 237 d time lag (day) Confidence curve at 99% Saar and Manga, Earth Planet. Sci. Lett. 214, , 23 Little, et al., J. Acoust. Soc. Am., 119, , 26 Telesca, BSSA, , 21

6 P w (f) P n (f) 1. Koyna-Warna (India) y 1/2 y 4 mo f c =.88 99% 2 mo 4 d f c =.5 99% f (1/day) 1-7 f(1/day) 2. w S n S w S, n S days since January 1, 21 Telesca, BSSA, , 21

7 1. Koyna-Warna (India) cross-correlation between n S and w S d.4 99% cross-correlation between n S2 and w S subperiod d 99% time lag (day) time lag (day) cross-correlation between n S2 and w S d subperiod time lag (day) Telesca, BSSA, , 21

8 1. Koyna-Warna (India) Diffusion equation and boundary conditions 2 P D 2 h P, P( t, h ) P e t Hydrological model i t D: Hydraulic diffusivity P: Pore pressure H: depth P P Solution e h 2D e i t h 2 D Plane wave: 1. attenuation coefficient 2. velocity 2 D 2D Decrease of the pore-pressure amplitude with depth h Periodic behavior of the pressure as a function of depth h and time t Telesca, BSSA, , 21

9 1. Koyna-Warna (India) Hydrological model Diffusivity D 2 h 2 t 2 =2 (year) -1 t=223 days h= mean depth h of the seismic events D=.2.18 m 2 /s Telesca, BSSA, , 21

10 W N 2. Açu (Brazil) Period: Jan 1987-Mar months since 1987 water monthly EQ counts Telesca, do Nascimento, Bezerra, Ferreira, NHESS, 12, 85, 212 Telesca, do Nascimento, Bezerra, Ferreira, in preparation, 213

11 2. Açu (Brazil) y water level Power spectrum analysis y EQ monthly count 99% P w.1 99% P n f(1/month) f(1/month) y water EQ.15 P w, P n f(1/mo) Telesca, do Nascimento, Bezerra, Ferreira, in preparation, 213

12 time lag (month) time lag (month) 2. Açu (Brazil) Cross-correlation analysis time variation of the cross-correlation: time window of 36 months shifting by 1 month through the overall record; the data included within such time window were cross-correlated and the results associated to the time of the last datum in the window a b c d months since months since 1987 Telesca, do Nascimento, Bezerra, Ferreira, in preparation, 213

13 3. Aswan (Egypt) 1981 Aswan Eq occurred 17 years after the starting of reservoir filling Temporal variations of shallow seismicity associated with a high rate of water level fluctuation, while no clear correlation with the deeper seismicity (Awad and Mizoue, 1995) Maximum correlation at timelag of 2 months during (depth h< 4 km, M> 2.) (Selim et al. 22) Seismicity rate correlates with the seasonal fluctuations of the lake level, indicating positive evidence for the Aswan seismicity to be reservoir-triggered in the (Mekkawi et al., 24)

14 3. Aswan (Egypt) Analysed period: 1 Jan 1982 to 31 Dec 21 Data Source: Bulletins of the Aswan Earthquake Regional Research Center Size of the whole catalogue: 791 Size of the catalogue after declusterization (Reasenberg (1985)): 3545 Mc=2.5 Telesca, Mohamed, ElGabry, El-Hady, Elenean, Chaos Solitons & Fractals, 45, 47, 212 Telesca, Lovallo, Mohamed, ElGabry, El-Hady, Elenean, ElBary, Physica A, 391, 2889, 212 Telesca, Lovallo, Mohamed, ElGabry, El-Hady, Elenean, ElBary, NHESS, 12, 1267, 212 Telesca, ElBary, Mohamed, ElGabry, NHESS, 12, 223, 212

15 3. Aswan (Egypt) Telesca, ElBary, Mohamed, ElGabry, NHESS, 12, 223, 212

16 3. Aswan (Egypt) Telesca, ElBary, Mohamed, ElGabry, NHESS, 12, 223, 212

17 3. Aswan (Egypt) Time-variant cross-correlation: time window of 6 years, moving through the data, with a shift of 1 month Telesca, ElBary, Mohamed, ElGabry, NHESS, 12, 223, 212

18 Cumulative Number 4. Enguri (Georgia) 1 3 Mc Heigth: 272 m Building period: Preliminary flooding of the territory started at the end of December Threshold magnitude Period of analysis: Size of declustered catalogue: 2131 Max mag: 4.7 Depth max: 32 km Mc: 1.6 b-value:.92 (whole Caucasus.72) Telesca, Matcharashvili, Chelidze, NHESS, 12, 195, 212

19 P(f) m N P(f) 4. Enguri (Georgia) 1 1 water level 1 y water level EQ number 2 a 1 b months since April w = f (1/month) a) 1 1 seismicity 1 s = f (1/month) b) Telesca, Matcharashvili, Chelidze, Zhukova, NHESS, 12, 2479, 212

20 V V V V variance of each component (% of the total) 4. Enguri (Georgia) 7 seismicity water level Singular spectrum analysis seismicity r 1 water level r order a) e) r 2 r b) f) r 3 r 3 c) g) r 4.3 r d) -.1 h) t (month) t (month) Telesca, Matcharashvili, Chelidze, Zhukova, NHESS, 12, 2479, 212

21 P(f) P(f) P(f) P(f) P(f) P(f) 4. Enguri (Georgia) seismicity a) r 1 water level e) r b) y c) 4 m d) y r 2 r 3 r f) 1 y y g) m h) r 2 r 3 r 4 1 seismicity ( ) r 1 15 m r 2 f (1/month) f (1/month) m 9 m r 3 8 m r 4 7 m f (1/month) f (1/month) Telesca, Matcharashvili, Chelidze, Zhukova, NHESS, 12, 2479, 212