During the winter of 1990-91, residents in the Sebago Lake Region of<br>southwestern Maine became alarmed by a noise phenomenon which they were convinced was<br>caused by a natural gas transmission pipeline in the area. The unexplained noises caused<br>residents to suspect the nearby transmission line. In response to these concerns, the pipeline<br>operator thoroughly checked the pipeline for potential safety problems. No leaks were detected<br>and all other safety checks had revealed that nothing was amiss.<br>An investigation was undertaken to study the source of the noise phenomenon on behalf of the<br>pipeline company. Local residents were interviewed and a network of 3-component<br>seismographs was installed to establish background vibration levels and to identify the source<br>of the disturbances. The seismographs used in this study can be set to record events over a wide<br>range of vibration levels. Area residents were given log books in which to describe any unusual<br>noise events and to record the time of occurrence.<br>Based on approximately two months of continuous monitoring in the study area, personal<br>interviews, a literature search for related vibration phenomena, and first-hand observations of<br>the noise phenomena by the author, we concluded that the loud noises were the result of<br>cryoseisms (‘lffostquakes”) or frost-induced microearthquake activity.<br>Cryoseisms are an unusual phenomena which occur under limited winter weather conditions in<br>northern climes. They can locally produce loud noises such as those described by residents in<br>this study as ‘a slamming door, ” “an automobile running into the side of the garage’: “a furnace<br>blowing up’: and “a rifle shot’: Cryoseisms are also frequently accompanied by minor fissures<br>which may be as wide as several millimeters at the ground surface and which re-heal with time.<br>Examples of fissures ji-om the current study will be presented. The mechanisms that produce<br>cryoseisms and the climatic conditions under which they occur will be described.


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