I’ve seen this phenomenon many times over the years, while walking the dog out behind our house. The cables wiggle between these two particular power poles, but NOT between the adjacent poles (or any others, along this pole line). There is no wind, no earthquakes, no herds of animals or large vehicles/machinery anywhere nearby when this is happening. I honestly have no idea why this happens sometimes. Thoughts? I mean, sure, it’s probably ghosts, right? But any other explanation would be appreciated…
Did you measure the distance between the poles? I suspect it’s different from all the other spans, so this one happens to have a resonant frequency that exactly matches whatever vibration source is already there (could be the tension too). As for sources of vibration, wind is probably it, even if it’s not strong. If it just happens to create the right frequency, the cable will vibrate just like a violin string.
No, I’ve never tried to quantify the variables in that way. Just out walking the dog, and notice this strange behavior from time to time. I always assumed the poles were placed a specific distance apart, but honestly, I’m not sure. I suppose if I ever have the urge to pace it out to get a good estimate, I will…
I immediately thought of the original Tacoma Narrows Bridge, which collapsed after wind caused a resonance to build up and literally shook itself apart: https://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)