a new case of reservoir triggered seismicity: govind ... · a new case of reservoir triggered...

8
A new case of reservoir triggered seismicity: Govind Ballav Pant reservoir (Rihand dam), central India Kalpna Gahalaut a , V.K. Gahalaut a, , M.R. Pandey b a National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, India b Department of Mines and Geology, Lainchur, Kathmandu, Nepal Received 21 November 2006; received in revised form 27 March 2007; accepted 9 April 2007 Available online 14 April 2007 Abstract We report here that seismicity near Govind Ballav Pant reservoir is strongly influenced by the reservoir operations. It is the second largest reservoir in India, which is built on Rihand river in the failed rift region of central India. Most of the earthquakes occurred during the high water stand in the reservoir with a time lag of about 1 month. We use the concept of coulomb stress change and use Green's function based approach to estimate stresses and pore pressure due to the reservoir load. We find that the reservoir increases coulomb stress on the nearby faults of the region that are favourably oriented for failure in predominantly reverse slip manner under the NNESSW compression and thus promotes failure. The above two factors make it an obvious, yet so far unreported case of reservoir triggered seismicity. © 2007 Elsevier B.V. All rights reserved. Keywords: Reserior triggered seismicity; Coulomb stress; Rihand reservoir; Peninsular India 1. Introduction Increases in the frequency of occurrence of earthquakes due to man's engineering activities have resulted from the reservoir impoundment, quarrying and mining, and fluid injection and extraction (McGarr and Simpson, 1997). However, earthquakes caused by reservoir impoundment are stronger than by any other engineering activities. So far globally about hundred sites of Reservoir Triggered Seismicity (RTS) have been reported which include at least eight sites from India, namely, Koyna, Warna, Bhatsa, Dhamni, Gandipet, Idukki, Mula and Sriramsagar (Gupta, 2002). According to the mechanism of RTS, reservoir load and/or induced pore pressure due to reservoir operations is the cause of triggering of earthquakes on critically stressed pre-existing faults in the vicinity of the reservoirs (Simpson, 1986; Gupta, 1992; McGarr and Simpson, 1997). In this article, we report a new case of RTS associated with the Govind Ballav Pant reservoir, central India (Fig. 1). The reservoir is located on the Rihand river, a tributary of Son river, India. The 92 m high Rihand dam was built in 1962 and the reservoir is the second largest reservoir in India occupying an area of about 45×15 km 2 having a maximum storage capacity of 10.6 km 3 , and a capacity of electric power generation of 300 MW. In this article, we analyse the correlation between the times of high water levels in the reservoir and occurrence of the maximum number of earthquakes, and simulate the effect of the reservoir on the nearby earthquake causative faults to verify that these earthquakes were triggered by the reservoir. Tectonophysics 439 (2007) 171 178 www.elsevier.com/locate/tecto Corresponding author. E-mail address: [email protected] (V.K. Gahalaut). 0040-1951/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2007.04.003

Upload: nguyenthien

Post on 13-Jun-2018

228 views

Category:

Documents


0 download

TRANSCRIPT

2007) 171–178www.elsevier.com/locate/tecto

Tectonophysics 439 (

A new case of reservoir triggered seismicity: Govind Ballav Pantreservoir (Rihand dam), central India

Kalpna Gahalaut a, V.K. Gahalaut a,⁎, M.R. Pandey b

a National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, Indiab Department of Mines and Geology, Lainchur, Kathmandu, Nepal

Received 21 November 2006; received in revised form 27 March 2007; accepted 9 April 2007Available online 14 April 2007

Abstract

We report here that seismicity near Govind Ballav Pant reservoir is strongly influenced by the reservoir operations. It is thesecond largest reservoir in India, which is built on Rihand river in the failed rift region of central India. Most of the earthquakesoccurred during the high water stand in the reservoir with a time lag of about 1 month. We use the concept of coulomb stresschange and use Green's function based approach to estimate stresses and pore pressure due to the reservoir load. We find that thereservoir increases coulomb stress on the nearby faults of the region that are favourably oriented for failure in predominantlyreverse slip manner under the NNE–SSW compression and thus promotes failure. The above two factors make it an obvious, yet sofar unreported case of reservoir triggered seismicity.© 2007 Elsevier B.V. All rights reserved.

Keywords: Reserior triggered seismicity; Coulomb stress; Rihand reservoir; Peninsular India

1. Introduction

Increases in the frequency of occurrence of earthquakesdue to man's engineering activities have resulted from thereservoir impoundment, quarrying and mining, and fluidinjection and extraction (McGarr and Simpson, 1997).However, earthquakes caused by reservoir impoundmentare stronger than by any other engineering activities. So farglobally about hundred sites of Reservoir TriggeredSeismicity (RTS) have been reported which include atleast eight sites from India, namely,Koyna,Warna,Bhatsa,Dhamni, Gandipet, Idukki, Mula and Sriramsagar (Gupta,2002). According to themechanism of RTS, reservoir loadand/or induced pore pressure due to reservoir operations is

⁎ Corresponding author.E-mail address: [email protected] (V.K. Gahalaut).

0040-1951/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.tecto.2007.04.003

the cause of triggering of earthquakes on critically stressedpre-existing faults in the vicinity of the reservoirs(Simpson, 1986; Gupta, 1992; McGarr and Simpson,1997). In this article, we report a new case of RTSassociated with the Govind Ballav Pant reservoir, centralIndia (Fig. 1). The reservoir is located on the Rihand river,a tributary of Son river, India. The 92 m high Rihand damwas built in 1962 and the reservoir is the second largestreservoir in India occupying an area of about 45×15 km2

having a maximum storage capacity of 10.6 km3, and acapacity of electric power generation of 300 MW.

In this article, we analyse the correlation between thetimes of high water levels in the reservoir and occurrenceof the maximum number of earthquakes, and simulatethe effect of the reservoir on the nearby earthquakecausative faults to verify that these earthquakes weretriggered by the reservoir.

172 K. Gahalaut et al. / Tectonophysics 439 (2007) 171–178

2. Tectonics and earthquakes of the region

The reservoir is located in a failed rift zone, which isknown as the Narmada–Son–Tapti failed rift zone. TheENE–WSW trending failed rift zone transects the Indianpeninsular shield area into northern and southern blocks(Fig. 1). It is seismically the most active region of thepeninsular India, which evolved during the Archean andProterozoic period (Mahadevan and Subbarao, 1999).Many prominent faults have been mapped in the regionbut the faults bounding the failed rift zone to the southare suggested to be active and have witnessed reac-tivation till quaternary period. Most of the earthquakeactivity is also suggested to be associated with thesouthern faults (Rao et al., 2002). The reservoir liesclose to and south of Son–Narmada South fault. Nu-merous NW–SE and NE–SW trending small neotec-tonic faults have also been mapped in the vicinity of the

Fig. 1. Broad tectonic features of the part of the failed rift region of Narmadepicentre of 1927 Son Valley earthquake (Ms 6.5), by Gutenberg and Richreported in the ISC and IMD catalogues during 1984–2004 (M≥3) while s(M≤3). Bold arrows show the direction of maximum compression due to plaF1, F2 and F3 and the Son Narmada South fault are the neotectonic faults (GSthe inset. Inset also shows the Indian and Nepalese national seismological n

reservoir (GSI, 2000), however, sense of motion onthese faults is not known (Fig. 1).

In past 100 years only one major earthquake, namelythe June 2, 1927, Son Valley earthquake (M 6 1/2;Gutenberg and Richter, 1954, p.207), has occurredwithin 100 km of the reservoir (Chandra, 1977). Threeestimates of epicentre are available (Fig. 1) and suggestvariation in the estimate of up to 100 km. The earth-quake is assumed to have occurred in the lower crust offailed rift regions of Narmada Son and Tapti, similar tothe March 14, 1938 Satpura (M∼6 1/4 Gutenberg andRichter, 1954) and May 21, 1997 Jabalpur earthquakes(Singh et al., 1999; Rao et al., 2002; Gahalaut et al.,2004). The rupture of the recent 1997 Jabalpurearthquake (Mw 5.8), which occurred about 300 kmWSWof the reservoir, is suggested to lie in the downdipparts of the Son–Narmada South fault. Focal mechan-isms of this (Singh et al., 1999) and 1970 Broach

a–Son and Tapti over a smooth topographic map. Three estimates ofter (1954), ISC and USGS, are also shown. Stars denote earthquakesmall circles denote epicentres by DMG during Jan. 1997–Dec. 1999te movement (Gowd et al., 1992). Dark brown colour faults, marked asI, 2000). The 1970 Broach and 1997 Jabalpur earthquakes are shown inetworks.

173K. Gahalaut et al. / Tectonophysics 439 (2007) 171–178

earthquake, Mw 5.4, (Chung, 1993), which occurred atthe western extreme of the failed rift zone (Fig. 1),suggest predominance of the compressive regime. Since1984, about sixty small magnitude (M≤3) earthquakeshave been reported in the vicinity of the reservoir by thenational network (Fig. 1) of India MeteorologicalDepartment (IMD) and International SeismologicalCentre (ISC). Prior to 1984, there is no documentaryevidence of earthquake occurrence in the region. How-ever, it does not imply that such earthquakes did notoccur prior to 1984 and after the impoundment of thereservoir in 1962. Probably they were missed due toabsence of nearby seismic stations. Incidentally, the year1984 approximately coincides with the period of world-wide strengthening of seismological network. However,from earthquake catalogues, it appears certain that nostrong or even moderate magnitude earthquake hasoccurred in the region since the reservoir impoundment.

Department ofMines andGeology, Kathmandu,Nepal(DMG), which operates a 17 station network across Nepal(Fig. 1), about 400 km north of the reservoir, has reportednumerous small magnitude (M≤3) earthquakes from thestudy region. These earthquakes cluster close to thereservoir (Fig. 1). The data from January 1997 toDecember 1999 only are available to us. Epicentres of

Fig. 2. Monthly frequency of earthquakes reported byDMG (M≤3) that occurrecorrelation function between the two time series. The correlation is the maximumtemporal variation of change in stress in wet state, ΔSw, at a point located at a

these earthquakes as reported by IMD, ISC and DMG,coincide within 10–15 km in a tight cluster around thereservoir, though their focal depths are unreliable. Weagree that the location of these earthquakes contains errorof about 10–15 km, but it does not change our results andinterpretation in any significant way. Occurrence ofearthquakes near the reservoir makes it imperative totest the hypothesis of RTS.

3. Temporal variation of seismicity

Temporal variation of the earthquakes reported byDMG that occurred within 30 km from the reservoir, andthe maximum water levels in the reservoir are shown inFig. 2. Frequency of earthquake occurrence is the lowestduring June–July in each year and then it increases. Thewater level in the reservoir is the minimum during lateMay and then it increases with the onset of monsooneach year. We discretized the two time series at equalinterval of 1 month and calculated the cross-correlation.The cross correlation coefficient between the two timeseries is 0.71 at an average lag of about a month betweenreservoir water level and frequency of earthquakeoccurrence. The correlation decreases to 0.67 if weconsider earthquakes within 50 km from the centre of

dwithin 30 km from the reservoir, the reservoir water levels and theCross-(0.71) at a time lag of about 1 month. Graph with dashed line shows the

depth of 8 km under the reservoir and the prominent earthquake cluster.

Fig. 3. Average monthly frequency of earthquakes (M≥3) in ISC and IMD catalogues during the period 1984–2004 along with the average reservoirwater levels.

174 K. Gahalaut et al. / Tectonophysics 439 (2007) 171–178

the reservoir. The diffused earthquake cluster north ofthe reservoir may not be correlated with the reservoirwater level variations as the correlation decreases to0.60 once we include it.

The only limitation here is that the catalogue is ofshorter duration. The IMD and ISC catalogues cannot beused for such quantitative correlation exercise, as there arenot many events in these catalogues and their complete-ness may also be doubtful. However, we qualitativelyanalysed the temporal variation in the occurrence of theseearthquakes reported by ISC and IMD since 1984. Asreported earlier, in the period from 1984–2004, 59earthquakes of MN3 occurred in the region. Maximumnumber of earthquakes occurred in the months ofDecember and January, followed by occurrences in themonths of February,March andApril (Fig. 3). Earthquakeoccurrences are the least in remaining months of the year.Even this correlation, though qualitative, indicates thatmajority of the earthquakes occurred in the periods afterhigh water level was attained in the reservoir. Thus thegood correlation between the water level and earthquakes(Figs. 2 and 3) suggests that the frequency of earthquakeoccurrence is influenced by the annual changes in thereservoir water levels.

4. Effect of reservoir operation on the earthquakecausative faults

We consider stress changes due to reservoir waterload and the pore pressure. Since most of the earth-

quakes appear to have occurred during the periods ofhigh water level in the reservoir, first we considered theeffect of reservoir water load alone in earthquaketriggering. In the subsequent analysis we included theeffect of pore pressure also.

4.1. Effect of reservoir water load

Following Chander and Kalpna (2000), we simulatedthe load of Rihand reservoir through a series ofrectangular loads. The load was uniform in eachrectangle but its magnitude decreased with distance ofthe rectangle upstream from the dam. The maximumwater depth was considered as 90 m at the dam. We usedformulas based on 3d Boussineq solutions (Jaeger andCook, 1969, p.281) to compute cumulative values of sixstress tensors. These stress tensors were used tocalculate change in normal (Δσ) and shear (Δτ) stresson a given fault plane, which were then used to calculatechange in stability in dry state, i.e., without consideringpore pressure, ΔSd, (=Δτ−μΔσ, where μ is the frictioncoefficient) due to reservoir load (Jaeger and Cook,1969; Gough and Gough, 1970; Bock, 1980) on theconsidered faults. Positive values of ΔSd suggestdestabilization and promote failure on the consideredplanes and vice-versa.

Unfortunately, focal mechanisms of the earthquakesthat occurred close to the reservoir are not available. Weassumed that these earthquakes accompanied similarmotion as was involved during 1997 Jabalpur and 1970

175K. Gahalaut et al. / Tectonophysics 439 (2007) 171–178

Broach earthquakes. It has been suggested that duringthese earthquakes reverse motion occurred on the southdipping plane (Singh et al., 1999; Gahalaut et al., 2004)which is consistent with the NE to NNE directedcompressional regime of central and peninsular India(Gowd et al., 1992). Thus we calculated ΔSd on thesouth dipping fault planes of 1997 Jabalpur (strike, ϕ61°, dip, δ 64° and rake, λ 74°) and 1970 Broachearthquake (ϕ 35°, δ 49° and λ 44°) at a depth of 10 kmassuming that all the earthquakes near the reservoiroccurred at shallow depth in the upper crust, as at deeperdepth, reservoir effects will not be very significant. Thisis in contrast with the focal depth of 36 km for the 1997Jabalpur earthquake (Singh et al., 1999), but consistentwith 11 km focal depth for 1970 Broach earthquake(Chung, 1993). Focal depths of both the earthquakes

Fig. 4. Stress changes ΔS (in kPa) on the SSW dipping planes (ϕ 120°, δ 70solution, shown at the top right) are shown. Geologically mapped neotectonicolour contours indicate the region of destabilization. (a)ΔSd at 8 km depth wcontour interval is 5 kPa. (c) ΔSw at 8 km depth (d) ΔSw in a vertical sectio

were determined from the waveform modeling (Chung,1993; Singh et al., 1999) and hence appear to be reliable.Region of increased ΔSd in both cases lie southeast ofthe reservoir, whereas the region of earthquakeoccurrence lie west of the reservoir. Thus the two didnot correlate in any significant way. Computations ofΔSd even on the north dipping planes did not producefavourable results. Thus we suggest that the reservoirload does not destabilize the faults of 1997 Jabalpur or1970 Broach earthquake type. We even changed thedepth at which ΔSd is calculated but the results andinterpretation do not change in any significant way.

Unfavourable results of the above section promptedus to search for the faults on which the reservoir effectswere favourable. We considered all the geologicallymapped faults in the vicinity of the reservoir for our

° and λ 120°, corresponding to the plane ‘a’ of the derived fault planec faults having similar orientation (F1, F2 and F3) are also shown. Redith contour interval of 10 kPa. (b)ΔSd in a vertical section along A–A′,n along B–B′.

176 K. Gahalaut et al. / Tectonophysics 439 (2007) 171–178

analysis. Throughout our analysis, the sense of motionon geologically mapped faults is chosen in such a wayso as to be consistent with NNE–SSW compression dueto plate tectonic forces. This is also a condition in theanalysis related to the RTS, as earthquakes will betriggered only on those faults which are criticallystressed for failure under the ambient stresses (Simpson,1986; McGarr and Simpson, 1997; Talwani, 1997;Gupta, 2002). The reservoir acts only as trigger. Thusunder the compressive environment of central andpeninsular India, all the faults present in the region willeither be reverse or strike slip faults, depending upon theorientation of the faults with respect to the NNE to NEdirected maximum compression (Gowd et al., 1992). Weconsidered the orientation of the geologically mappedfaults and performed a grid search to estimate the dipdirection, dip amount and slip direction of these faults insuch a way that the reservoir causes destabilization onthese faults in the region of earthquake occurrences. Thecomputations of ΔSd were done at several depths buthere we show ΔSd at 8 km depth (Fig. 4a), where theeffect of the reservoir load is most pronounced (Fig. 4b).We find that WNW–ESE oriented geologically mappedneotectonic faults (GSI, 2000), shown as F1, F2 and F3

in Figs. 1 and 4, with δ of 70°±10° and λ of 120°±10°,having strike of about N120° are destabilized by thereservoir load in the region of prominent earthquakecluster reported by DMG and ISC (Fig. 4). Specifically,the east–west trending south dipping Son–NarmadaSouth fault, the largest fault in the region, did notproduce destabilization in the region of earthquakeoccurrence. It caused destabilization north of it. This wasexpected, as a reservoir located in the hanging wall willstabilize a thrust fault, rather than destabilizing it(Roeloffs, 1988). The faults F1, F2 and F3 have beenmapped, before reservoir impoundment in 1962, by theGeological Survey of India (GSI), in their district levelmap series (e.g., see geological and tectonic maps ofSarguja, Koriya, Sidhi and Mirzapur districts publishedby GSI) and are shown in Figs. 1 and 4. The derived faultplane solution corresponding to the above plane is alsoshown in Fig. 4. In an effort to further strengthen ouranalysis, we performed the grid search to identify thestrike along with the dip and rake of the fault and foundthat the above estimated planes (ϕ 120°, δ 70° andλ 120°) are the only fault planes on which the effect ofreservoir is favourable in the region of intenseearthquake activity. We also show an east–west verticalcross section of ΔSd across the reservoir, in which it isseen that at all depths, the region west of the reservoirexperiences destabilization due to reservoir load. Anominal value of 0.65 for μ is assumed in these

calculations. Change in μ by ±0.2 does not alter thepattern of destabilization in any significant way.

4.2. Effect of pore pressure

We calculate stress changes in wet state, i.e., consid-ering the pore pressure,ΔSw (=Δτ−μ(Δσ−ΔP), whereΔP is the pore pressure due to reservoir operationssince its impoundment started in 1961. Change innormal (Δσ) and shear (Δτ) stresses due the reservoirare calculated in the same manner as in the previoussection. ΔP is calculated by solving the followinginhomogeneous diffusion equation,

Cj2P ¼ A

ATP � B

3h

� �;

where c is the hydraulic diffusivity, B is the Skempton'scoefficient and θ / 3 is the mean stress. The value of c,hydraulic diffusivity constant was considered to be10 m2/s, by trial and error method, so as to give a timelag of about 1 month at a point beneath the maximumseismicity at an assumed depth of 8 km. The adoptedvalue of c is consistent also with Talwani and Acree's(1984) estimates derived from seismicity observationsnear various reservoirs worldwide. Higher value of cdecreases the time lag and increases the magnitude ofpore pressure, and vice-versa. B varies from 0 to 1, hereit is considered as 0.7 (Talwani et al., 1999). Thesolution of above equation is given by Kalpna andChander (2000). Pore pressure due to cyclic loading andunloading develops gradually in the initial periods (till1970), but later on, pore pressure, and hence ΔSw,mimics the pattern of annual cycle of water levelchanges in the reservoir with a time lag (Fig. 2).

Considering the lag of 1 month between the waterlevel and monthly frequency of earthquakes, wecalculated ΔSw on a plane at depth of 8 km, after1 month of maximum water level in the reservoir. Werepeated the exercise of the previous section to computeΔSw and found that the pattern in the zone of stability didnot change significantly from the previous corres-ponding cases. Thus even after considering the porepressure the region of increased ΔSw corresponding tothe 1997 Jabalpur and 1970 Broach earthquake faultsdoes not coincide with the region of earthquakeoccurrence. However, the results of grid search methodsuggested that once again faults with ϕ 120°±10°,δ 70°±10° and λ 120°±10° are destabilized by thereservoir load and induced pore in the region of prom-inent earthquake cluster reported by DMG and ISC(Fig. 4).

177K. Gahalaut et al. / Tectonophysics 439 (2007) 171–178

The east–west vertical cross section of ΔSw acrossthe reservoir (Fig. 4d) suggests that the region west ofthe reservoir experiences destabilization due to reservoiroperations at all depths. However, the effect is mostpronounced at about 8 km. The analysis suggests thatconsideration of pore pressure not only leads to increasein the magnitude of stress changes (ΔSwNΔSd) on theconsidered fault, it also leads to an increase in the regionof destabilization and now the region of destabilizationencompasses the entire region of earthquake activitynear the reservoir.

We computed temporal variation of ΔSw (Fig. 2) at apoint that lies at 8 km depth under the reservoir andwhere the increased ΔSw is the maximum (Fig. 4c). Itcan be seen that earthquakes do not appear to haveoccurred during the low water stand, even though theeffect of water load was to destabilize the fault evenduring that period (Fig. 2). Thus the analysis implies thatthe faults in the region are critically stressed for failureunder compressive regime and a small increase in stresschange due to reservoir operation, by about 25 kPa only,corresponding to an annual increase of water load by10–15 m (Fig. 2), triggers earthquakes on these faults.Presence of critically stressed faults is also supported bythe observation that this region is the seismically mostactive region of peninsular India.

Thus the above analyses pertaining to the quantita-tive effect of reservoir operation on the seismogenicfaults suggest that the reservoir operations destabilizethe nearby neotectonic faults.

5. Concluding remarks

Several factors control earthquake triggering by thereservoir, important of them are, reservoir dimensions;annual changes in the reservoir water level; ambientstresses and presence of faults and their orientation withrespect to the ambient stresses, etc. (Simpson, 1986). Inthis case the Govind Ballav Pant reservoir on Rihandriver is very large, in fact the second largest in India,having annual water level changes of the order of about12±2 m, it is situated in a failed rift region of Narmada–Son–Tapti, which is seismically the most active region inthe peninsular India (Gahalaut et al., 2004) and whereseveral faults have been mapped (Fig. 1). These factorsmake it an ideal site where reservoir may triggerearthquakes on the nearby faults. A good correlationbetween temporal variation of seismicity and reservoirwater levels (Fig. 2) suggest a possible case of reservoirtriggering. Our simulation using a Green's function-based approach related to stability change on theearthquake causative neotectonic faults due to reservoir

operation (Fig. 4) supports the view that water levelchanges in the reservoir have caused pore pressurechanges at hypocentral depths on the pre-existing faults,which are favourably oriented, to trigger the earth-quakes. This makes it a persuasive, yet so far unreported,case of triggered seismicity due to the reservoir loading.

In the region of interest, we have no knowledge aboutthe earthquake occurrence immediately after the reser-voir impoundment in 1962 and before 1984, the lateryear marks the year of beginning of reliable earthquakecatalogues. But good correlation between earthquakesduring 1984–2004 (for MN3 from ISC and IMDcatalogues) and during 1997–99 (for Mb3 from DMGcatalogue) with reservoir water level possibly suggeststhat the reservoir triggered earthquakes occurred in thisregion after the impoundment and the reservoircontinued to trigger earthquakes even after 40 years ofimpoundment. Cases of continued seismicity near areservoir have been reported from elsewhere as well,e.g., Koyna–Warna in India (Gupta, 2002); Lake Meadin USA (Talwani, 1997), Aswan in Egypt (Mekkawiet al., 2004), Açu in Brazil (do Nascimento et al., 2004)etc.

Acknowledgements

We are thankful to the Central Electricity Authorityfor providing Rihand reservoir water levels, DMG,Nepal for providing the microseismicity data (acquiredunder DASE, France and DMG collaboration), and R.S.Dattatrayam and G. Suresh of IMD, New Delhi forproviding the earthquake data. We benefited from thecomments of A.McGarr, Pradeep Talwani, Harsh Gupta,Kusala Rajendran and two anonymous reviewers. Wethank Director, NGRI, R.K. Chadha and M. Ravi Kumarfor their support.

References

Bock, Y., 1980. Load induced stresses and their relation to initial stressfield. J. Geophys. 48, 94–100.

Chander, R., Kalpna, 2000. On categorising induced and naturaltectonic earthquakes near new reservoirs. Eng. Geol. 46, 81–92.

Chandra, U., 1977. Earthquakes of Peninsular India — a seismotec-tonic study. Bull. Seismol. Soc. Am. 67, 1387–1413.

Chung, W.Y., 1993. Source parameters of the rift-associated intraplateearthquakes in peninsular India: the Bhadrachalam earthquake ofApril 13, 1969 and the Broach earthquake of March 23, 1970.Tectonophysics 225, 219–230.

do Nascimento, A.F., Cowie, P.A., Lunn, R.J., Pearce, R.G., 2004.Spatio-temporal evolution of induced seismicity at Açu reservoir,NE Brazil. Geophys. J. Int. 158, 1041–1052.

Gahalaut, V.K., Rao, V.K., Tewari, H.C., 2004. On the mechanism andsource parameters of the deep crustal Jabalpur earthquake, India, of

178 K. Gahalaut et al. / Tectonophysics 439 (2007) 171–178

May 21, 1997: constraints from aftershocks and change in staticstress. Geophys. J. Int. 156, 345–351.

Gough, D.I., Gough, W.I., 1970. Stress and deflection in thelithosphere near Lake Kariba — I. Geophys. J. 21, 65–78.

Gowd, T.N., Rao, S.V.S., Gaur, V.K., 1992. Tectonic stress field in theIndian subcontinent. J. Geophys. Res. 97, 11879–11888.

GSI, 2000. Seismotectonics atlas of India. Geological Survey of India,Calcutta, India, p. 87.

Gupta,H.K., 1992. Reservoir InducedEarthquakes. Elsevier, Amsterdam.355 pp.

Gupta, H.K., 2002. A review of recent studies of triggered earthquakesby artificial water reservoirs with special emphasis on earthquakesin Koyna, India. Earth-Sci. Rev. 58, 279–310.

Gutenberg, B., Richter, C.F., 1954. Seismicity of the Earth, 2ndedition. Princeton Univ. Press, Princeton, New Jersey.

Jaeger, J.C., Cook, N.G.W., 1969. Fundamentals of Rock Mechanics.Methuen, London, p. 515.

Kalpna, Chander, R., 2000. Green's function based stress diffusionsolutions in the porous elastic half space for time varying finitereservoir loads. Phys. Earth Planet. Inter. 120, 93–101.

Mahadevan, T.M., Subbarao, K.V., 1999. Seismicity of the Deccanvolcanic province—an evaluation of some endogenous factors. In:Subbarao, K.V. (Ed.), Deccan Volcanic Province. Geol. Soc. IndiaMem., vol. 43, pp. 453–484.

McGarr, A., Simpson, D., 1997. Keynote lecture: a broad look atinduced seismicity. Rockbursts and Seismicity in Mines. Balkema,Rotterdam, pp. 385–396.

Mekkawi, M., Grasso, J.R., Schnegg, P.A., 2004. A long-lastingrelaxation of seismicity at Aswan reservoir, Egypt, 1982–2001.Bull. Seismol. Soc. Am. 94, 479–492.

Rao, N.P., Tsukuda, T., Koruga, M., Bhatia, S.C., Suresh, G., 2002.Deep lower crustal earthquakes in central India: inferences fromanalysis of regional broadband data of the 1997 May 21 Jabalpurearthquake. Geophys. J. Int. 148, 132–138.

Roeloffs, E.A., 1988. Fault stability changes induced beneath areservoir with cyclic variations in water level. J. Geophys. Res. 93,2107–2124.

Simpson, D.W., 1986. Triggered earthquakes. Annu. Rev. EarthPlanet. Sci. 14, 21–42.

Singh, S.K., Dattatrayam, R.S., Shapiro, N.M., Mandal, P., Pacheco,J.F., Midha, R.K., 1999. Crustal and upper mantle structure ofpeninsular India and source parameters of the 21 May 1997Jabalpur earthquake (Mw=5.8): Results from a new regionalbroadband network. Bull. Seismol. Soc. Am. 89, 1631–1641.

Talwani, P., 1997. On the nature of reservoir-induced seismicity. PureAppl. Geophys. 150, 473–492.

Talwani, P., Acree, S., 1984. Pore pressure diffusion and themechanism of reservoir-induced seismicity. Pure Appl. Geophys.122, 947–965.

Talwani, P., Cobb, J.S., Schaeffer, M.F., 1999. In situ measurements ofhydraulic properties of a shear zone in northwestern SouthCarolina. J. Geophys. Res. 104, 14993–15003.