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Selected problems of seismic event location
340A
GEOLOGY:EARTHQUAKES
968024 Mass wasting triggered by the 5 March 1987 Ecuador earthquakes R. L. Schuster, A. S. Nieto, T. D. O’Rourke, E. Crespo & G. Plaza-Nieto, Engineering Geology, 42(l), 1996, pp l-23. The economic and social losses directly due to earthquake shaking were small compared to the effects of catastrophic earthquake-triggered mass wasting and flooding. About 600 mm of rain fell in the region in the month preceding the earthquakes; thus, the surficial soils had high moisture contents. Slope failures commonly started as thin slides, which rapidly turned into fluid debris avalanches and debris flows. Rock and earth slides, debris avalanches, debris and mud flows, and resulting floods destroyed about 40 km of the Trans-Ecuadorian oil pipeline and the only highway from Quito to Ecuador’s northeastern rain forests and oil fields. Estimates of total volume of earthquake-induced mass wastage ranged from northeastern rain forests and oil fields. Estimates of total volume of earthquake-induced mass wastage ranged from 75-110 million m3. Economic losses were about USS 1 billion. Approximately 1000 deaths were a consequence of mass wasting and/or flooding. (from Authors) %8025 Local site effects in the nortbern North Sea based on singlestation spectral ratios of ORS recordings K. Atakan & J. Havskov, Terru Nova, 8(l), 1996, pp 22-33. In this study, a technique recently proposed by Nakamura (1989) is used to evaluate site response using spectral ratios of horizontal vs. vertical components of earthquake recordings from a temporary ocean bottom seismograph (OBS) network in the northern North Sea and a permanent OBS at Oseberg oil field. Comparison with results obtained from the standard spectral ratios, indicate that the method is applicable also to subsea conditions, and the estimates obtained in this study indicate similar amplification factors to those obtained previously from analytical techniques. The results obtained on the earthquake data provide an encouraging alternative to previously used analytical techniques for estimating local site response. (from Authors) 968026 Unexpected shock rocks an ‘aseismic’ area S. C. Stiros, Eos, 76(50), 1995, pp 513,519. A strong earthquake with surface wave magnitude 6.6 hit the small town of Grevena in northwest Greece on May 13,1995. This event was just one of the frequent, strong @I 2 6.0) earthquakes that hit Greece but cause relatively few deaths. There are two main reasons for this phenomenon: houses in most parts of Greece are designed to withstand earthquakes, and epicenters of most shocks are in the sea. In the case of the Grevena earthquake, the epicenter of the shock was inland, close to inhabited areas, while most of the houses were old and of low strength. Most people alerted by a small foreshock were luckily outside of the buildings that collapsed. This event proves that lack of fatalities does not necessarily suggest weak earthquake magnitude. Paleoseismological investigations revealed that at least some of the ‘aseismic’ or ‘low’seismicity areas in Greece have been affected by major earthquakes with magnitudes around 7.0. (from Author) 968027 Earthquake prediction in the region of the SayanoSbushenskoe hydroelectric station by means of the dam’s measuring systems A. N. Marchuk, Hydrotechnical Construction, 29(8), 1995, pp 453-459; translated from: Gidrotekhnicheskoe Stroitel’stvo, 8, 1995, pp 34-38. A method of recording and predicting earthquakes by means of the measuring systems of high dams is proposed. High concrete dams located in seismically active mountain regions near tectonic deformations are sensitive to geodynamic processes in the surrounding geological environment. Their developed multifunctional measuring systems are able to record strain, hydrogeological, geochemical, and other types
of precursors by a unified system by means of standard measuring instruments. The regions of the sites of such dams and their reservoirs are sufficiently well studied in geological, seismotectonic, and seismological respects. Systematized onsite observations begun during construction permit having long observed series and using them for statistical analysis for finding a correlation between the measured parameters of state of the ‘dam-foundation-reservoir’ system and characteristics of the earthquakes that occurred. In the presence of induced seismic&y there are broad opportunities for testing measuring systems with respect to earthquake parameters. (from Journal translation) 968028 Seismic networks in the mainland of China Li Qiang, Bulletin - International Institute of Seismology & Earthquake Engineering, 29, 1995, pp 21-42. China is one of the most seismically active countries in the world. In order to meet the requirements of monitoring, timely reporting and prediction for large earthquake and to provide information for engineering construction and scientific research work, at present, there are more than 700 seismic stations in the mainland of China. In the present paper, the basic situation of seismic networks is brieily described. (from Author) 968029
Distribution of the damage caused by the earthquake of Jan. 17,1995 and its geomorphic environment as seen from fallen tombstones (in Japanese) T. Kawasaki, R. Nomura & M. Oya, Geographical Review of Japan, Series A, 69(l), 1996, pp 39-50. On Jan. 17,1995, the Southern Hyogo Prefecture Earthquake struck Kobe, including the surrounding cites. The extent of the damage brought about by this earthquake upon tombstones was examined. A geomorphological classification was made in order to examine the relation between landform types and the results of the mrvey. A certain kind of tombstone, made up of three or four stones arranged in steps, was selected for this survey. The survey was conducted to find out what percentage of this type of tombstone in each cemetery had had its upper level toppled over by the earthquake (hereafter known as PFt). The examples show that PFt was mainly determined by each location’s landform type, even for areas near the earthquake fault. PFt reflects the ground character of the landform, considering the fact that high PFt values were observed on areas with soft ground foundation such as alluvial plain, present fan, and backmanh. (from English summary) 968030
Selected problems of seismic event location W. Debski, Publications - Institute of Geophysics, Polish Academy of Sciences, series k4, M-19(281), 1995, pp 125-134. Hypocenter location is the very first task in the process of studying any seismic event. The accuracy that can be acoomplished depends on many elements, e.g., the accuracy of phase arrival readings, the number and distribution of stations, knowledge of velocity field and number of different registered phases. Here the influence of the number and type of registered phases (Ps, P, and PM) on the accuracy of seismic source location is studied. It is shown that the use of a few different phases instead of a single one essentially improves the location accuracy. (from Author) 968031 Short note on automatic location of seismic events B. Ruxek, Publications - Institute of Geophysics, Polish Academy of Sciences, series h4, M-19(281), 1995, pp 135-140. An algorithm that integrates both the search for phase onsets and finding optimum location into one compact procedure is described. The algorithm is based on the Hilbert transform of input seismograms (energy envelope) and locationdependent onsets-search. (Author)
GEOLOGY:EARTHQUAKES
968024 Mass wasting triggered by the 5 March 1987 Ecuador earthquakes R. L. Schuster, A. S. Nieto, T. D. O’Rourke, E. Crespo & G. Plaza-Nieto, Engineering Geology, 42(l), 1996, pp l-23. The economic and social losses directly due to earthquake shaking were small compared to the effects of catastrophic earthquake-triggered mass wasting and flooding. About 600 mm of rain fell in the region in the month preceding the earthquakes; thus, the surficial soils had high moisture contents. Slope failures commonly started as thin slides, which rapidly turned into fluid debris avalanches and debris flows. Rock and earth slides, debris avalanches, debris and mud flows, and resulting floods destroyed about 40 km of the Trans-Ecuadorian oil pipeline and the only highway from Quito to Ecuador’s northeastern rain forests and oil fields. Estimates of total volume of earthquake-induced mass wastage ranged from northeastern rain forests and oil fields. Estimates of total volume of earthquake-induced mass wastage ranged from 75-110 million m3. Economic losses were about USS 1 billion. Approximately 1000 deaths were a consequence of mass wasting and/or flooding. (from Authors) %8025 Local site effects in the nortbern North Sea based on singlestation spectral ratios of ORS recordings K. Atakan & J. Havskov, Terru Nova, 8(l), 1996, pp 22-33. In this study, a technique recently proposed by Nakamura (1989) is used to evaluate site response using spectral ratios of horizontal vs. vertical components of earthquake recordings from a temporary ocean bottom seismograph (OBS) network in the northern North Sea and a permanent OBS at Oseberg oil field. Comparison with results obtained from the standard spectral ratios, indicate that the method is applicable also to subsea conditions, and the estimates obtained in this study indicate similar amplification factors to those obtained previously from analytical techniques. The results obtained on the earthquake data provide an encouraging alternative to previously used analytical techniques for estimating local site response. (from Authors) 968026 Unexpected shock rocks an ‘aseismic’ area S. C. Stiros, Eos, 76(50), 1995, pp 513,519. A strong earthquake with surface wave magnitude 6.6 hit the small town of Grevena in northwest Greece on May 13,1995. This event was just one of the frequent, strong @I 2 6.0) earthquakes that hit Greece but cause relatively few deaths. There are two main reasons for this phenomenon: houses in most parts of Greece are designed to withstand earthquakes, and epicenters of most shocks are in the sea. In the case of the Grevena earthquake, the epicenter of the shock was inland, close to inhabited areas, while most of the houses were old and of low strength. Most people alerted by a small foreshock were luckily outside of the buildings that collapsed. This event proves that lack of fatalities does not necessarily suggest weak earthquake magnitude. Paleoseismological investigations revealed that at least some of the ‘aseismic’ or ‘low’seismicity areas in Greece have been affected by major earthquakes with magnitudes around 7.0. (from Author) 968027 Earthquake prediction in the region of the SayanoSbushenskoe hydroelectric station by means of the dam’s measuring systems A. N. Marchuk, Hydrotechnical Construction, 29(8), 1995, pp 453-459; translated from: Gidrotekhnicheskoe Stroitel’stvo, 8, 1995, pp 34-38. A method of recording and predicting earthquakes by means of the measuring systems of high dams is proposed. High concrete dams located in seismically active mountain regions near tectonic deformations are sensitive to geodynamic processes in the surrounding geological environment. Their developed multifunctional measuring systems are able to record strain, hydrogeological, geochemical, and other types
of precursors by a unified system by means of standard measuring instruments. The regions of the sites of such dams and their reservoirs are sufficiently well studied in geological, seismotectonic, and seismological respects. Systematized onsite observations begun during construction permit having long observed series and using them for statistical analysis for finding a correlation between the measured parameters of state of the ‘dam-foundation-reservoir’ system and characteristics of the earthquakes that occurred. In the presence of induced seismic&y there are broad opportunities for testing measuring systems with respect to earthquake parameters. (from Journal translation) 968028 Seismic networks in the mainland of China Li Qiang, Bulletin - International Institute of Seismology & Earthquake Engineering, 29, 1995, pp 21-42. China is one of the most seismically active countries in the world. In order to meet the requirements of monitoring, timely reporting and prediction for large earthquake and to provide information for engineering construction and scientific research work, at present, there are more than 700 seismic stations in the mainland of China. In the present paper, the basic situation of seismic networks is brieily described. (from Author) 968029
Distribution of the damage caused by the earthquake of Jan. 17,1995 and its geomorphic environment as seen from fallen tombstones (in Japanese) T. Kawasaki, R. Nomura & M. Oya, Geographical Review of Japan, Series A, 69(l), 1996, pp 39-50. On Jan. 17,1995, the Southern Hyogo Prefecture Earthquake struck Kobe, including the surrounding cites. The extent of the damage brought about by this earthquake upon tombstones was examined. A geomorphological classification was made in order to examine the relation between landform types and the results of the mrvey. A certain kind of tombstone, made up of three or four stones arranged in steps, was selected for this survey. The survey was conducted to find out what percentage of this type of tombstone in each cemetery had had its upper level toppled over by the earthquake (hereafter known as PFt). The examples show that PFt was mainly determined by each location’s landform type, even for areas near the earthquake fault. PFt reflects the ground character of the landform, considering the fact that high PFt values were observed on areas with soft ground foundation such as alluvial plain, present fan, and backmanh. (from English summary) 968030
Selected problems of seismic event location W. Debski, Publications - Institute of Geophysics, Polish Academy of Sciences, series k4, M-19(281), 1995, pp 125-134. Hypocenter location is the very first task in the process of studying any seismic event. The accuracy that can be acoomplished depends on many elements, e.g., the accuracy of phase arrival readings, the number and distribution of stations, knowledge of velocity field and number of different registered phases. Here the influence of the number and type of registered phases (Ps, P, and PM) on the accuracy of seismic source location is studied. It is shown that the use of a few different phases instead of a single one essentially improves the location accuracy. (from Author) 968031 Short note on automatic location of seismic events B. Ruxek, Publications - Institute of Geophysics, Polish Academy of Sciences, series h4, M-19(281), 1995, pp 135-140. An algorithm that integrates both the search for phase onsets and finding optimum location into one compact procedure is described. The algorithm is based on the Hilbert transform of input seismograms (energy envelope) and locationdependent onsets-search. (Author)