Triggered Earthquakes at Koyna, India IASPEI 2009, Cape Town, South Africa National Geophysical Research Institute (Council of Scientific and Industrial Research), Hyderabad, India - Harsh Gupta, D.Shashidhar, K.Mallika, N.Purnachandra Rao, D.Nagesh, HVS.Satyanarayana, S.Saha, RT.Babu Naik and VP.Dimri

Globally, there are over 100 Artificial Water Reservoir sites where triggered earthquakes have occurred Majority of the sites where triggered earthquakes of M ≥ 5 occurred are in SCR

KOYNA SITE Most damaging RTS, event of December 10, 1967 Continued RTS since 1962 M ≥ 5 earthquakes: 1967, 1968, 1973, 1980, 1993-94, 2000, 2005 Common Characteristics Nucleation Pore Fluid Pressure

Seismicity of the Koyna Region

Energy Released in Koyna region: The Max. Credible Earthquake (MCE) considered for Koyna: M = 6.8 Empirical relation used: Log E = 1.5 M + 11.8, (M = magnitude) Using the above relation EMCE = 1022 Energy released so far: Case 1: E = 1 x EM6.3 + 20 x EM 5.5 + 200 x EM 4.5 = 10(21.25) + 10(20.5) + 10(18.55) = 1021.94 Percentage of MCE = 1021.94 / 1022 = 87 % Case 2: E = 1 x EM6.3 + 20 x EM 5.3 + 200 x EM4.3 = 10(21.25) + 10(19.75) + 10(18.25) = 1021.51 Percentage of MCE = 1021.51 / 1022 = 32 % -------------------------------------------------------------------------------------- Considering the average of the above 2 extreme cases, About 50% of energy may be released in Koyna

Real time monitoring at Koyna since August 2005.

At Koyna Reservoir After several years as early as August 17,2005, a peak water level of 657.784m at koyna was reached Fastest loading rate ever: 627.685 to 657.784m in just 55 days at Koyna. Kaiser effect is observable

At Warna Reservoir From a level of 594.06m on 23rd June 2005, it has risen to 626.9m on 15th August 2005. This has been the fastest loading when the water level rose by 32.84m in just 53 days.

An Earthquake of M~5 may occur at Koyna Kaiser effect was observable at both the reservoirs. An enhanced seismic activity during August,2005 was observed and a M 4.2 earthquake occurred on 14th August 2005. Two clusters were also identified nearer to Warna reservoir. Based on the above factors a forecast was made on 25th August 2005 that ‘an earthquake of M~5 may occur at Koyna region in the weeks to follow’. “And this forecast has come true with an earthquake of M 4.8 on 30th August 2005, Origin Time:08:53:18.1 (UTC), with location 17.147oN, 73. 780oE and depth is 6.9km” -CURRENT SCIENCE, VOL 89, 10TH SEP 2005, Gupta et. al.

Precursory Seismicity patterns

Total no of events in a area of 10km radius: 21 30 August 2005: Earthquake of M 4.8 Nucleation time: 110 hrs Total no of events in a area of 10km radius: 21 Largest being M 2.1 50 hrs Preceding Nucleation only 2 events

Total no of events in a area of 10km radius: 27 13 November 2005: Earthquake of M 4.0 Nucleation time: 160 hrs Total no of events in a area of 10km radius: 27 Largest being M 3.0 50 hrs Preceding Nucleation only 3 events

Total no of events in a area of 10km radius: 30 26 December 2005: Earthquake of M 4.2 Nucleation time: 150 hrs Total no of events in a area of 10km radius: 30 Largest being M 2.9 50 hrs Preceding Nucleation only 6 events

17 April 2006: Earthquake of M 4.7 Nucleation time: 380 hrs Total no of events in a area of 10km radius: 50 Largest being M 2.7 50 hrs Preceding Nucleation only 2 events

Events preceding the Main shock during the Nucleation time   Main earthquake Duration of Nucleation Period (hours) No. of events before the Main earthquake M 1.0-1.9 M 2.0-2.9 M 3.0- 3.9 Largest earthquake 50 hrs prior to beginning of nucleation period 30 August 2005 M 4.8 110 13 8 2.6 2 13 November 2005 M 4.0 160 18 1 3.0 3 26 December 2005 M 4.2 150 22 2.9 6 17 April 2006 M 4.7 380 40 10 2.7

Forecast of an M~4 earthquake in the Koyna region 16th May 2006 at 7pm, IST “On the basis of the data available from 7 seismic stations operating in the Koyna region, we have identified a nucleation, which started on 12th May, 2006. This may lead to the occurrence of an M~4 earthquake in the next 15 days. This shallow earthquake ( focal depth < 8 km ) will occur within a radius of 10 km centered at 17.10N, 73.80E. On the basis of our previous experience of studying nucleation-preceding earthquakes in the Koyna region, we expect this earthquake to occur over the next 15 days time (till 31st May, 2006), with a 50% probability.” -JOUR.GEOL.SOC.INDIA, VOL.68, JULY2006, Gupta et. al.

Nucleation Preceding an M 4.2 Earthquake Successfully Forecasted Event observing Nucleation Earthquake of M 4.2 in Zone-A occurred on 21st May 2006 at 20:29:01.2 UTC. The epicenter of this earthquake (17.1710N, 73.7770E), lies within 10 km of the predicted epicenter. The focal depth is 4.7 km. Nucleation time lasted for 250 hrs

Forecast of M 3.4 EQ Occurred on 14th Oct 2007 2007, October 8 - 10 2007, October 8 – 25 Successful Forecast of M 3.4 EQ Occurred on 14th Oct 2007

Forecast of M 3.0 EQ Occurred on 2nd July 2008 2008, June 13 – 4 July 2008, June 13 - 28 Successful Forecast of M 3.0 EQ Occurred on 2nd July 2008

Three Zones of Seismic Activity in the Koyna Region

A New Zone Of Seismic Activity March 2007 Kandwan

Conclusions Triggered earthquakes have continued to occur in the Koyna region for over 4 decades now. The seismic activity being localized, with no other seismic activity in the vicinity, makes Koyna an ideal location for studying earthquake precursors. We have found that earthquakes of M~4 are generally preceded by a nucleation lasting 100 to 400 hours before the main shock. Proper monitoring makes it possible to make short term forecasts. However, even in a small region like Koyna, we find that currently from among the three active areas, precursory nucleation is observed in only one area. We have also discovered a new zone of seismic activity in Koyna for the past two years which gets activated in the months of February/March. This is possibly due to creation of another small reservoir which gets filled up seasonally.

Thank you

Earthquakes of M ≥ 3.5 in Zone - A S.No Day of occurrence Origin Time (h m s) Latitude (oN) Longitude (oE) Depth (km) Magnitude (ML) Remarks 1 14-08-2005 06 33 28.0 17.161 73.793 5.0 4.2 - 2 30-08-2005 08 53 18.1 17.147 73.780 6.8 4.8 3 13-11-2005 03 56 08.0 17.134 73.783 4.0 Common nucleation, being only one week apart 4 20-11-2005 18 50 42.0 17.209 73.765 5.9 4.1 5 26-12-2005 10 46 06.3 17.149 73.786 5.8 6 17-04-2006 16 39 59.41 17.145 73.785 3.9 4.7 7 21-05-2006 20 29 01.2 17.171 73.777 8 19-01-2007 19 59 23.39 17.143 2.5 3.8 9 20-08-2007 19 15 54.5 73.784 3.6 4.3 10 19 31 45.4 17.136 73.789 After shock of # 9 11 14-09-2007 01 05 21.2 17.139 73.778 4.4 3.5

Earthquakes of M ≥ 3.5 in Zone - B S.No Date of occurrence Origin Time (h m s) Latitude (oN) Longitude (oE) Depth (km) Magnitude (ML) 1 24-11-2007 10 57 47.1 17.111 73.705 3.1 4.8 2 11 35 45.6 17.107 73.710 3.3 4.6 3 12 35 28.0 17.108 73.711 2.1 4.1 4 12 36 24.1 17.102 2.8 3.5 5 14 11 26.9 17.109 73.704 3.6

Earthquakes of M ≥ 3.5 in Zone - C S.No Date of occurrence Origin Time ( h m s ) Latitude (oN) Longitude (oE) Depth (km) Magnitude (ML) 1 30-03-2006 05 08 00.9 17.334 73.755 11.4 3.5 2 31-03-2006 07 31 46.6 17.339 73.766 5.7 3 18-03-2008 04 13 26.5 17.281 73.728 2.1 3.8 4 29-07-2008 19 10 54.2 17.324 73.747 3.2 4.3 5 16-09-2008 21 47 15.4 17.297 73.771 7.8 4.8

Non-nucleation Phase at Zone - B Earthquakes of M~4 in Zone-B occurred on 24 November 2007. Aftershocks followed after the Main earthquakes in a tight cluster.

Non-nucleation Phase at Zone - C Earthquake of M 4.8 in Zone-C occurred on 16 September 2008. Absence of foreshock activity near epicentral region is clearly visible.

Zones Bearing Nucleation/Non-nucleation for Moderate Earthquakes in the Koyna Region Zone A Zone B Zone C Nucleation preceded not preceded M 3.5 – 3.9 2 3 M 4.0 – 4.4 5 1 M 4.5 – 4.9 -

Successful forecasts in the Koyna Region On the basis of clean nucleation pattern: Successful forecasts in the Koyna Region

Reservoir Water Levels (2005, 2006)

Reservoir Water Levels (2007-2008)

Seismicity levels of the Koyna-Warna area (Aug’05-9July’06) Seismicity map Histogram