Mining Subsidence Induced Fault Reactivation
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MACROSEISMIC SURVEY Roger M. W. Musson British Geological Survey, Edinburgh, UK
Definition The term “macroseismic survey” refers to the process of gathering information on how strongly an earthquake was felt in different places. Discussion It has long been standard practice in earthquake investigation to gather information on the distribution of effects of any recent earthquake. Indeed, before the introduction of reliable seismometers, this was really the only way to study an earthquake. Generally, the results of such a study are presented as a map of intensity, often contoured as isoseismals. A macroseismic survey generally comprises two parts. The most heavily damaged area needs to be examined firsthand, and the damage to individual buildings recorded. This task ideally should be conducted in collaboration with engineers qualified to assess the original strength of the damaged buildings. This is referred to as a field investigation of the earthquake. Data collection for the wider felt area of the earthquake, at non-damaging intensities, is usually done via questionnaires. Various strategies for the dissemination of questionnaires have been practiced in the past, including appeals for information published in newspapers, sending questionnaires to local officials, and maintaining a network of volunteer observers who can be relied on to fill in details after an earthquake has occurred. Today, the dominant method of collecting questionnaire data is over the internet. After even a moderatesized event in a populated area, tens of thousands of responses can be collected very quickly via an institute’s web site, and these can then be processed in real time using
an automatic intensity assessment algorithm. This also has the great advantage that the results of the survey are visible immediately on the web site, rather than appearing only in a journal paper or bulletin some months later, and this is an excellent method of conveying seismological data to the general public in a timely and informative way.
Bibliography Musson, R. M. W., 2002. Intensity and intensity scales. In Bormann, P. (ed.), New manual of seismological observatory practice (NMSOP). Potsdam: GFZ. Musson, R. M. W., and Cecić, I., 2002. Macroseismology. In Lee, W. H. K., Kanamori, H., Jennings, P. C., and Kisslinger, C. (eds.), International Handbook of Earthquake and Engineering Seismology. San Diego: Academic, pp. 807–822. Wald, D. J., Quitoriano, V., Dengler, L. A., and Dewey, J. W., 1999. Utilization of the Internet for rapid community intensity maps. Seismological Research Letters, 70(6), 680–697.
Cross-references Intensity Scales Internet, World Wide Web and Natural Hazards Isoseismal Magnitude Measures Seismograph/Seismometer
MAGMA Catherine J. Hickson1,2, T. C. Spurgeon2, R. I. Tilling2,3 1 Magma Energy Corp., Vancouver, BC, Canada 2 Alterra Power Corp., Vancouver, BC, Canada 3 Volcano Science Center, U.S. Geological Survey, Menlo Park, CA, USA
Synonyms Liquid rock; Molten rock
P.T. Bobrowsky (ed.), Encyclopedia of Natural Hazards, DOI 10.100
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