| Facing earthquake disasters governments and scientific researchers all over the world are sparing no effort to look for efficient ways to fight against the damage.After an earthquake, the off-site rapid assessment, a vital part of rapid response, directly influences the timeliness of the earthquake relief work and the analysis of the disaster loss. The rapid assessment plays an important part in the relief work, offering lots of information for action which helps a lot. The assessment refers to several key factors such as the epicenter, magnitude, rupture direction, and intensity attenuation model, each of which can have a great effect on the final results. Many relief actions exhibit a problem that sometimes the meizoseismal area is not accurately located which leads to a deviation of the assessment result and eventually affects the relief work. This problem, which this thesis tries to figure out, mainly lies in the error resulting from the determination of the macro epicenter and the direction of the intensity attenuation of a major quake.In view of the problem appearing in the rapid assessment, this thesis suggests a solution named“aftershock analysis”, which mainly deals with two of the key factors, the epicenter and the rupture direction of the quake.Under the circumstances that little information about the disaster situation can be available in a short time after a shock, besides studying the disaster evaluation model, information mining is also a good method of improving the assessment result. As a result of the limitations of observational methods, aftershocks were seldom used in disaster assessment before. However, with the development of the observational techniques, the aftershocks of a much higher accuracy can be completely recorded. And obviously, a new approach for the rapid disaster evaluation can be offered with the introduction of the aftershocks.First of all, the development of the earthquake relief work is discussed and the research situation of aftershocks is comprehensively analyzed. Then in combination with seismogenic theories, a seismogenic model is established. While 40 groups of earthquake samples, which are supposed to be the fundamental research data, are obtained through the collection, rearrangement and selection of large amounts of earthquake data since 1970. Finally, the intensity attenuation relationships of those selected samples are figured out using traditional methods and the method of“aftershock analysis”, respectively. The results of this work are summarized as follows.1. The method of determining the location relationship between the macro epicenter and the micro epicenter by the centroid of aftershocks is practicable.Although the locations of the centroids of aftershocks are different in different earthquakes, 80 percent of them are located between the macro epicenter and the micro epicenter with uniform distribution of angular deviations, which proves that the assumption of the location of the centroid of aftershocks in the seismogenic model is reasonable.The analysis of the distribution relationship among the centroid of aftershocks, the macro epicenter and the micro epicenter suggests that the relationship can be divides into two patterns approximately. One pattern is that the macro epicenter can be inferred according to the micro epicenter and the centroid of aftershocks if the centroid lies between these two epicenters. The other one is that the centroid can be regarded as the macro epicenter if the centroid is close to the macro epicenter. Regardless of the focal mechanism solutions, which obviously affect the distribution of the aftershocks, this work merely studies the overall distribution relationship, and therefore the relationship isnot described by a specific mathematical formula.2. The method of aftershock analysis for determining the intensity attenuation direction is feasible.According to statistics, the accuracy of the method of determining the intensity attenuation direction by faults is 80 percent with a high precision while that of the method of aftershock analysis is 70 percent, slightly lower. Under the condition of insufficient or few fault data available, the method of the aftershock analysis can supply a more solid basis for the rapid assessment. Certainly, the result can be more accurate when these two methods are used in combination with each other. 3. The Aftershock Analysis meets the requirement of timeliness of the rapid assessment.As time passes by, the number of the aftershocks increases, meanwhile the location of the centroid changes. It is shown that the location of the centroid of the aftershocks of 87.5 percent samples tends to be stable 6 hours after the main shock, which has a little difference from those in 12 hours, 24 hours and even 30 days.It is of the same rule with the intensity attenuation direction determination. The direction six hours after the earthquake is tending towards stability,and it is consistent with that of all the aftershocks for 70 percent of the samples.As a result, this work considers the time of 6 hours after the earthquake as the time that the method of aftershock analysis takes effect, and the result obtained at this time is rapid and accurate.It is a new attempt for this work to introduce the method of aftershock analysis into the rapid determination of the intensity attenuation relationship. Thus the result obtained is no doubt a small breakthrough and can be put into practice after the completion of the determination process.The difficulties showing up in the research together with the problems needed to be noticed in future study are presented briefly below.1. The accuracy of the aftershocks of recent years is reliable due to the convenient observations, but that of the aftershocks of earlier years, especially those before the 1970s is uncertain, which probably leads to the deviation of the result. And this problem is still under consideration in this work.2. The earthquake parameters are not so precise, and the error range can be as much as 10m or so, which has a great effect on the determination. Fortunately, the accuracy of the parameters will be enhanced a lot with the development of monitoring techniques.3. The intensity distribution mainly reflects the influence of the earthquake on human beings, and therefore the population distribution has a great effect on the intensity zoning. If the earthquake occurs in no man’s land or sparsely populated land, the intensity distribution cannot be zoned according to the damage by the earthquake. This work hasn’t taken this situation into account, which maybe sometimes results in a big deviation.4. Each earthquake has its own unique focal mechanism, which affects the distribution of the aftershocks a lot. Nowadays, it is easier to obtain the focal mechanism solutions shortly after an earthquake, and this will be taken into consideration in further research and a better result is expected.5. Besides the location, the information the aftershock records offer includes the magnitude, the focal depth, and the focal mechanism solutions and so on. This study merely takes advantage of the factor of location, a better result is certainly obtained if the other factors are taken into account and different weight values are given according to different aftershocks. |
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