KOYNA-EARTHQUAKE FORECAST
September 24, 2007
Earthquake forecast in Koyna possible: paper
BY MRITYUNJAY BOSE
MUMBAI: Nestled in the Western Ghats, the Koyna region has been prone to earthquakes. The seismic activity near the Koyna Dam has been a matter of concern for the district administration, geologists and seismic experts. Now a new study carried out by a team of Hyderabad-based National Geophysical Research Institute reveals that earthquake forecast appears feasible at Koyna.
The Koyna zone is a classic example of reservoir-triggered seismicity (RTS), where artificial water reservoir-triggered earthquakes have been occurring in a restricted area of 20x30 sq km for the last 44 years. Since the impoundment of Koyna reservoir 44 years ago and nearby Warna reservoir 21 years ago, 19 earthquakes of measuring over 5 in earthquake magnitude scale (M) have rocked the region. Besides this, several thousand smaller earthquakes triggered in the region making it the most significant site among the 100 sites of artificial water reservoir-triggered earthquakes, globally.
Clear foreshock nucleation patterns were visible for most of the M4+ earthquakes in the Konya during August 2005-May 2006. "Based on such a nucleation pattern, an M4+ earthquake was forecast in Koyna on May 16, 2006, which came true on May 21, 2006. It appears that isolated, well-monitored sites like Koyna are probably most suitable locales for the pursuit of short-term earthquake precursory studies in future," according to a research paper published in the September issue of 'Current Science'. While, the researchers predicted M4+ intensity quake on May 16, on May 21 when it rocked the region, it was M4.2 – a fairly accurate prediction.
The continued seismic activity makes it an excellent natural laboratory to conduct earthquake studies and forecasting. The study by the team comprising – Harsh Gupta, D Shashidhar, Metilda Pereira, Prantik Mandal, N Purnachandra Rao, M Kousalya, H V S Satyanarayana and V P Dimri – points out that detailed monitoring of water levels in 21 boreholes and other studies such as radon emission, repeat GPS and gravity measurements will strengthen the forecast system in this particular site. However, it still needs to be verified, how such type of forecasting of earthquakes be attempted in other regions with different tectonic set-up.
As regard the data analysis, the research paper points out that the seismic activity has been monitored by a closely-spaced network of seven modern seismic stations. Beginning from August 2005, data are collected from each station every 24 hours and analysed on a daily basis. Around the middle of August 2005, it was seen that both at Koyna and Warna reservoirs the rate of loading was higher than previous years, and levels higher than previous maximum was reached. This implied that Koyna region would have higher level of seismic activity than previous years.
The study reveals that an interesting situation arose during the middle of May 2006. By the afternoon of May 16 last year, 21 events of M 2.0-2.9 and 29 events of M 1.0-1.9 had occurred, the largest being M2-7 during the preceding 107 hrs in a small area. The focal depths ranged between two-eight kms. "A nucleation was therefore inferred. During the 50 hours preceding the beginning of nucleation, seismic activity was much lower," the report said. On the basis of the data collected, it was identified that a nucleation started on May 12 and this may lead to an occurance of M4 in the next 15 days – an earthquake of M 4.2 occurred on May 21. "The success of forecasting the May 21, 2006 earthquake of M 4.2 gives hope to improve our understanding of quakes in the Koyna region," the research paper said.
(This article was first published in The Maharashtra Herald, Pune)
Earthquake forecast in Koyna possible: paper
BY MRITYUNJAY BOSE
MUMBAI: Nestled in the Western Ghats, the Koyna region has been prone to earthquakes. The seismic activity near the Koyna Dam has been a matter of concern for the district administration, geologists and seismic experts. Now a new study carried out by a team of Hyderabad-based National Geophysical Research Institute reveals that earthquake forecast appears feasible at Koyna.
The Koyna zone is a classic example of reservoir-triggered seismicity (RTS), where artificial water reservoir-triggered earthquakes have been occurring in a restricted area of 20x30 sq km for the last 44 years. Since the impoundment of Koyna reservoir 44 years ago and nearby Warna reservoir 21 years ago, 19 earthquakes of measuring over 5 in earthquake magnitude scale (M) have rocked the region. Besides this, several thousand smaller earthquakes triggered in the region making it the most significant site among the 100 sites of artificial water reservoir-triggered earthquakes, globally.
Clear foreshock nucleation patterns were visible for most of the M4+ earthquakes in the Konya during August 2005-May 2006. "Based on such a nucleation pattern, an M4+ earthquake was forecast in Koyna on May 16, 2006, which came true on May 21, 2006. It appears that isolated, well-monitored sites like Koyna are probably most suitable locales for the pursuit of short-term earthquake precursory studies in future," according to a research paper published in the September issue of 'Current Science'. While, the researchers predicted M4+ intensity quake on May 16, on May 21 when it rocked the region, it was M4.2 – a fairly accurate prediction.
The continued seismic activity makes it an excellent natural laboratory to conduct earthquake studies and forecasting. The study by the team comprising – Harsh Gupta, D Shashidhar, Metilda Pereira, Prantik Mandal, N Purnachandra Rao, M Kousalya, H V S Satyanarayana and V P Dimri – points out that detailed monitoring of water levels in 21 boreholes and other studies such as radon emission, repeat GPS and gravity measurements will strengthen the forecast system in this particular site. However, it still needs to be verified, how such type of forecasting of earthquakes be attempted in other regions with different tectonic set-up.
As regard the data analysis, the research paper points out that the seismic activity has been monitored by a closely-spaced network of seven modern seismic stations. Beginning from August 2005, data are collected from each station every 24 hours and analysed on a daily basis. Around the middle of August 2005, it was seen that both at Koyna and Warna reservoirs the rate of loading was higher than previous years, and levels higher than previous maximum was reached. This implied that Koyna region would have higher level of seismic activity than previous years.
The study reveals that an interesting situation arose during the middle of May 2006. By the afternoon of May 16 last year, 21 events of M 2.0-2.9 and 29 events of M 1.0-1.9 had occurred, the largest being M2-7 during the preceding 107 hrs in a small area. The focal depths ranged between two-eight kms. "A nucleation was therefore inferred. During the 50 hours preceding the beginning of nucleation, seismic activity was much lower," the report said. On the basis of the data collected, it was identified that a nucleation started on May 12 and this may lead to an occurance of M4 in the next 15 days – an earthquake of M 4.2 occurred on May 21. "The success of forecasting the May 21, 2006 earthquake of M 4.2 gives hope to improve our understanding of quakes in the Koyna region," the research paper said.
(This article was first published in The Maharashtra Herald, Pune)
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