A review of recent studies of triggered earthquakes by artificial water reservoirs with special emphasis on earthquakes in Koyna, India

Abstract

Triggering of earthquakes by filling of artificial water reservoirs is known for over six decades. As of today, over 90 sites have been globally identified where earthquakes have been triggered by filling of water reservoirs. The question of earthquakes triggered by artificial reservoirs has been addressed and reviewed in a number of papers and books. In the present review, the book “Reservoir-Induced Earthquakes” by Gupta [Gupta, H.K., 1992. Reservoir-Induced Earthquakes. Elsevier, Amsterdam, 364 pp.], which contains all the necessary information on this topic till 1990, has been taken as the base. An effort has been made to add information on this important topic gathered over the last 10 years. Koyna, India continues to be the most significant site of artificial-water-reservoir-triggered earthquakes. During 1990s, two events exceeding M 5 and several smaller events occurred in the vicinity of Koyna, and recently impounded Warna Reservoir. Detailed studies have addressed the relocation of earthquakes, stress drop, nucleation, migration and other important aspects of these earthquakes. In a unique experiment, twenty-one 90- to 250-m deep borewells have been drilled in the seismically active Koyna–Warna region and the water levels are continuously monitored. Step-like coseismic changes of several centimeters have been observed in some wells associated with a few M≥4 events.

Detailed tomographic studies conducted on one of the best recorded triggered earthquake sequence at Lake Oroville in California revealed that this sequence was associated with a southwest dipping structure characterized by low velocity, while in adjacent areas, seismic activity occurs in regions of higher velocity. Similar investigations in Aswan showed that shallow activity is associated with low P-wave velocity. Several new reservoir sites that have triggered earthquakes have been reported during 1990s. The most important being Srinagarind Dam in Thailand, which had an M 5.9 earthquake and the sequence had all the characteristics of triggered earthquake sequences. New theoretical work, particularly the effect of pore fluid pressure in anisotropic rocks and its implication in triggered seismicity is an important development. However, much more needs to be done to fully comprehend the role of artificial water reservoirs in triggering earthquakes.

Introduction

Huge artificial water reservoirs are created all over the world for generation of hydroelectric power, flood control and irrigation purposes. Triggering of earthquakes by artificial water reservoirs was for the first time pointed out by Carder (1945) at Lake Mead in the United States of America. Damaging earthquakes exceeding M 6 occurred at Hsinfengkiang, China in 1962; Kariba, Zambia–Zimbabwe Border in 1963; Kremasta, Greece in 1966; and Koyna, India in 1967. The December 10, 1967, Koyna earthquake of M 6.3 is so far the largest and most damaging reservoir-triggered earthquake. It claimed about 200 human lives, injured about 1500 and rendered thousands homeless. Civil works at Koyna town suffered major damage. The Hsinfengkiang and Koyna earthquakes caused damage to dams themselves. Other reservoir-triggered earthquakes such as those at Kariba, Zambia; Kremasta, Greece; Oroville, CA; Aswan, Egypt; and Srinagarind, Thailand had caused damage in nearby towns and villages. The occurrence and potential of triggered earthquakes has caused major modifications of civil works and engineering projects. The Hsinfengkiang Dam (Shen et al., 1974) in the People's Republic of China was strengthened twice before the occurrence of the March 20, 1962 induced earthquake of magnitude 6.1. The disposal of waste fluid through injection into the ground at Rocky Mountain Arsenal had to be discontinued because of triggered earthquakes (Evans, 1966). The possibility of triggered seismicity was one of the major factors in terminating the construction of Auburn Dam in California (Allen, 1978). The design parameters of the proposed 260-m-tall Tehri Dam in the foothills of Himalaya, India continue to be questioned and reexamined to ensure the dam's capability to resist earthquakes. Earlier, as pointed out by Allen (1982) and Simpson (1986), there is a general reluctance on the part of the Engineering Committee, globally, to accept the significance or even existence of the phenomenon of reservoir-triggered seismicity. However, there has been some change in this attitude. In a recent report of the US Committee on Large Dams (USCOLD, 1997), it is concluded that there can be an increase in occurrence of reservoir-triggered seismicity (RTS) during the period of reservoir water level changes and the possibility of RTS should be considered for every reservoir deeper than 80–100 m. Allen (1982) stated 18 years ago that “From a purely economic point of view, not to speak of public safety, the problem of reservoir-induced earthquakes deserves far more attention than it currently is receiving in most parts of the world”. This observation still holds good.

Most of the work carried out on various aspects of artificial-water-reservoir-induced seismicity till 1990 has been reviewed by Gupta (1992). Since 1990, many workshops and symposia have been organized on this topic, and a wealth of papers have appeared in several volumes. (e.g. Gupta and Chadha, 1995, Knoll and Kowalle, 1996, Talebi, 1997, Talebi, 1998). Additionally, there are some good articles by Meade (1991), USCOLD (1997) and McGarr and Simpson (1997).

In the following, an effort has been made to review important work reported during the 1990s on the topic of artificial-water-reservoir-induced earthquakes. Koyna, on west coast of India, continues to be the most significant site of reservoir-triggered seismicity (RTS). Several new investigations and reports appeared during the 1990s. A triggered earthquake sequence has been reported from Thailand at Srinagarind reservoir with the main shock magnitude of M 5.9. Important work reported from Oroville, CA and Aswan, Egypt is commented upon. Seeber et al. (1996) have made a case for the Latur earthquake of 1993 in south India to be a triggered event. However, others do not consider it triggered (Rastogi, 1994).