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|Node deployment along the intersection of the Denali Fault and Parks Highway (Denali Imaging)
We'll deploy two simultaneous arrays of seismometers along the Denali fault where it intersects the Parks highway. One array will be 300 nodes spaced 500m along the train track; we've received permission from the Alaska Railroad corporation to deploy on their land 40 feet from the tracks and in addition they will support us with a road-rail vehicle. The railroad runs approximately perpendicularly to the fault; our main targets are (a) the structure of the moho across the Denali and Hines Creek faults (currently a subject of debate), (b) upper crustal structure via ambient seismic noise imaging, and (c) detection of local seismicity. During the winter months, only 2 trains per day use the tracks, which will keep nuisance signals to a minimum. The experiment needs to conclude before the end of April when traffic picks up and the rivers melt. The second array will be composed of 100 seismometers with 20 meter spacing across the fault at a nearby location that has been trenched for paleoseismic studies. The target will be the upper 1-3km damage zone structure, which will be imaged using ambient noise and trapped waves generated by local earthquakes. We will likely apply several other techniques including fault zone head wave analysis, first-arrival polarization analysis, ambient noise cross-correlation at high frequency, and fault zone resonance spectral analysis. The location is moderately forested and rugged and will be conducted primarily by snowshoe hiking. The principal investigators Carl Tape and Amir Allam successfully conducted a nodal seismometer deployment under similar conditions in March-April of 2016 along the Denali fault where it is intersected by the Richardson Highway 100km to the east of the present work. Much of the field area is accessible via a frozen river, which will greatly facilitate the deployment during the midwinter months February to March. Both Allam and Tape scouted this field area during March 2018 to develop a thorough site plan and understand the logistics. For both arrays, the instruments will be shallowly buried (~2 inches) for noise reduction and safety. During February and March, there will be virtually no human activity, and very little wildlife. We will accomplish the burial via hand auger, digging rod, and sharpshooter shovels. The locations will be taken with precise RTK gps which will allow easy recovery; we also have a metal detector as a diligent contingency plan. Allam and Tape have extensive experience with the terrain and the instruments. Allam has conducted a dozen nodal deployments in conditions ranging from urban to desert to Alaskan winter and has never lost an instrument for any reason. These arrays offer a unique opportunity to study fault structure at multiple scales across the longest and oldest strike-slip fault in the world. The field conditions will be challenging and will provide a beautiful demonstration of the considerable utility of the nodal seismometers. This work is fully supported by two NSF grants, 1736248 and 1736223.
|Digital Object Identifier (DOI)
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