The Second Meeting of the Asian Seismological Commission and Symposium on ‘Earthquake Hazard Assessment and Earth’s Interior Related Topics’ (ASC98) was held at the National Geophysical Research Institute (NGRI), Hyderabad, India during 1-3 December, 1998. The event was sponsored by International Association for Seismology and Physics of the Earth’s Interior, (IASPEI), Indian National Science Academy (INSA), Department of Science and Technology, Govt. of India (DST) and Council of Scientific and Industrial Research (CSIR), India. About 200 abstracts were received and about 150 delegates, with 70 participants from outside India from 26 countries attended the event.
Dr. V S Ramamurthy, Secretary, Department of Science & Technology, Government of India, inaugurated the event. Dr. Harsh K Gupta, Director NGRI and President Asian Seismological Commission (ASC) presided over the function. In his presidential address, Dr. Gupta welcomed all the office bearers, delegates, and other dignitaries on behalf of ASC and the host, NGRI. He traced back the process of origin of ASC and touched upon the theme of earthquake forecasting, the cherished goal of all the seismologists for more than a century. Though there is pessimism in the scientific community, he expressed hope that medium term forecasting may be possible in specific areas/situations. He also stressed the importance of internationally coordinated project GSHAP (Global Seismic Hazard Assessment Program ) in the present day context. Dr. Peter Wyllie, President, IUGG, Dr. Claude Froidevaux, President, IASPEI, Dr. E.R.Engdahl, Secretary-General, IASPEI, Dr. Zhu Chuanzhen, Secretary-General, ASC, and Dr. S Varadarajan, President INSA also addressed the gathering.
The Inaugural function was followed by three ASC lectures, delivered by Y T Chen on “Source parameters of the Nov.8, 1997 Mani, northern Tibet earthquake”, by E R Engdahl on “High resolution P wave imaging of mantle structure beneath southern Asia “ and by H K Gupta on “Major and great earthquakes in the Himalayan region”. Regular scientific sessions, concerned with papers on 8 broad topics followed subsequently in three parallel sittings.
Session S1 titled ‘Earthquake Prediction and Seismic Hazard Assessment’ covered: Hazard studies – considering the probabilities of earthquake motion without reference to any particular earthquake, used for building codes; Alerts – where unusual activity has been detected, and there is an enhanced but unspecified possibility of a large earthquake; Forecasts – where it may be possible to estimate a probability that an earthquake in a magnitude range may occur in a specified area in a particular time period; Prediction – where it is said that an event of particular magnitude will occur at a particular time and place. Alternative methods for quantification of earthquake recurrence in source zones were presented. Fault slip rates from GPS measurements and palaeoseismology now provide constraints on the character of seismicity. The significance of using spectral acceleration, velocity and displacement for attenuation studies was clearly demonstrated by an analysis of the Jabalpur, India earthquake in 1997. A comprehensive system for society- seismologist interaction that has been established in Armenia was described in a presentation. In Session S2 titled ‘Process and structure of the lithosphere’ (30 papers), research papers included recent theoretical developments in robust statistical analysis to analyze model quality in tomography, numerical synthesis of post and coseismic deformation. Towards data analysis and modelling, research contribution carried wide spectrum like surface wave tomography of Iran and Indian ocean, a reinterpretation of Indian DSS profile in Dharwar craton and Bengal basin. Application of broad-band seismological data to infer the nature of Indian crust and Eurasian continent was demonstrated. Session S3 was concerned with “Earthquakes and Tectonics of the Intra and Interplate Regions“ . The papers on the Himalayan earthquakes discussed essentially the seismotectonic assessment of the region covering the entire fold belt examining implications of different models.. Papers presenting earthquake data in the Indian peninsular shield from microseismic to macroseismic range were able to bring out strong possibilities of moderate earthquakes in the continental interior as evidenced from recent earthquakes in Latur and Jabalpur. Some interesting features of rift tectonics were revealed by teleseismic deep sounding studies of the Narmada-Son valley. Very interesting studies focusing on active tectonics of other parts of the world were also discussed in some papers, which highlighted the active slip rates in known fault zones and the associated intensive seismicity. The regions particularly covered in these presentations included Red River province in Vietnam, Central Alborz and Thailand. The subducted pacific lithosphere in the Tonga-Kermadec area was well described in one of the papers. One other paper dwelt on the analysis of seismic quiescence and the genesis of the formation of spatio-temporal gap to infer interesting aspects of resulting seismicity. In support of this study, typical examples from Japan were discussed.
Session S4 covered topics on “Physics of Earthquake Processes“. Earthquake interaction and deformation processes, studied theoretically as well as experimentally, were reported. Source processes, as well as source parameters are retrieved by moment tensor inversion and empirical Green function techniques. Meaningful results of these studies were presented. Artificial as well as natural source discrimination problem was also discussed theoretically and studied by using observation data.
Session S5 was devoted to “Recent Devastating Earthquakes”. Papers related to recent 1997 Jabalpur earthquake and 1993 Latur earthquake in India, some recent Iranian earthquakes, 1997 Jioshi strong swarm in western China and its tectonic implications. One paper presented the revised parameters of Jabalpur earthquake after synthesizing data of different organizations. Another paper presented focal mechanisms of Latur aftershocks obtained by waveform modelling. Hydrological changes related to Latur earthquake was reported. Two papers described a long and prominent surface fault developed due to 1997 Ghaen-Birjand earthquakes of M 7.1. They explained the unusually long fault length involved in this earthquake due to multiple earthquakes in a short interval.
Session S6 titled “Induced Seismicity“ dealt with various aspects of reservoir and mine induced seismicity were presented. Reports on ongoing studies at the site of the three Gorges dam (China) and the experiments at Koyna-Warna Reservoirs (India) emphasized the need to continue to study the processes and problems of induced seismicity. At Koyna, site of ongoing seismicity, a unique experiment is in program that is to monitor pore pressure changes in deep wells. Importance of experiments and observations at the sites of mine induced seismicity was stressed in the various papers presented. Sites of induced seismicity provide natural laboratories for understanding the mechanism of earthquakes. Discussions focused on the background conditions that make a site vulnerable to seismic activity. Since a reservoir cannot induce earthquakes unless the failure conditions are favourable it was felt that the term triggered earthquakes is more appropriate term to describe seismicity associated with reservoirs. This is also in line with the recent recommendation of a report released in 1997 by the U.S. Committee on Large Dams (USCOLD).
Session S7 titled “Heat flow and crustal thermal structure“ was intended to mainly attract new heat flow and radiogenic heat production data from continental segments, and their interpretation towards understanding the thermal structure of the continental crust. There were five oral presentations. One paper dealt with new heat flow and radiogenic heat production data obtained from four areas of the Archaean Dharwar province of the southern Indian shield. The main results were (i) a low heat flow regime for the Dharwar province, and (ii) a uniform mantle heat flow in the range 11.5 to 14.5 mW m-2. In another work, the Moho temperature beneath the central part of the Narmada-Son lineament has been estimated as 650((50(C, and the thermal thickness of the lithosphere comes out as 80 km. One paper presented a stochastic view of the thermal structure incorporating Gaussian coloured noise correlation structure of thermal conductivity and obtained error bounds on the crustal temperature estimates. Another paper dealt with 2-D thermal modelling to delineate crustal thermal structure of the Cambay region along a 220 km long deep seismic sounding profile. Surface heat flow values have been derived and Curie-isotherm depths ranging from about 21 to 25 km along the profile have been estimated. Another paper brought forth data on radiogenic heat producing elements for all the major rock types of the Southern Granulite Terrain of the southern Indian shield using in-situ gamma ray spectrometric measurements at ~ 200 sites. The data would be useful for building up a crustal thermal structure for the region.
Session S8 dealt with ‘Current trends in dissemination of seismological and other geophysical information and educating the public on seismic disaster mitigation’. As the name suggests all the papers presented dealt with this important theme of direct relevance to public. There were oral/poster presentations on RADIUS initiative, public education, regional seismic information systems, observatory practice and training programs.
A workshop was held on GARNET (Global Alliance of Regional Networks) program. The discussions focused addressed the importance of global networking of regional seismic networks with special emphasis to the mapping of deep Earth structure, by coordinating an exchange program of waveform segments for specific earthquakes large enough to provide useful data on deep Earth structure. The details of GARNET project were presented.
A closing ceremony was held on the afternoon of Dec.3 marking the formal ending of the three-day long ASC98 conference. Various delegates spoke on a variety of topics of general interest to seismologists from Asian countries. Emphasis was laid on the need of pooling efforts amongst not only the Asian countries but also from other parts of the world to study the origin and evolution of earthquake, for effective reduction of earthquake hazards and for understanding the physics of the earthquake process. It was announced that the 3rd meeting of the ASC will be held in 2000 to be hosted by the Institute of Geophysics, Tehran University, Iran.
Pre-meeting Training Course (Nov. 15-30, 1998)
International training Course on “Seismic Monitoring , Data analysis, and Exchange “ , with Dr. H K Gupta, vice-president, IASPEI and Prof. Peter Bormann, Chairman, IASPEI Sub-Committee on Training, as the Course Directors was organised during November 15-30, 1998. The faculty consisted of the scientist from NGRI, GeoForschungs Zentrum Potsdam (GFZ), Germany, the University of Bergen, Norway, Kinematrics SA, Switzerland and the India Meteorological Department. The course was attended by 25 trainees (selected from amongst 70 applicants): India 8, China 6, Iran 3, Oman 2 and one each from Uzbekistan, Kyrgyzstan, Yemen, Indonesia, Georgia and Zambia. The main topics covered in this course were: basics of seismology and seismometry, data acquisition, observatory practice, data analysis and exchange, and earthquake source parameters and mechanisms. A series of lectures, practical experiments in the field and plenty of hands-on exercises on computers were held. Nearly a dozen SUN workstations and Pentium PCs were available to the participants. Also, scientific excursion to the epicentral site of the devastating Latur 1993 earthquake which is situated about 250 kms away from Hyderabad, was organized. UNESCO, IDNDR, COSTED , IASPEI, GFZ , DST and INSA sponsored the training course.