New discovery - stormquakes

[Randi]

There is an interesting new discovery reported in Geophysical Research Letters (GRL) that intersects with USS Jamestown observations during the Sitka Hurricane of 26-27 October 1880. I have long wondered about the brief earthquake activity reported during the storm, but didn't give it much credence. Now, as Dr. Fan has confirmed, it turns out they might well be 'stormquakes'.

Paper (open): http://myweb.fsu.edu/wfan/FMDHCF_GRL_2019.pdf
NPR: https://www.npr.org/2020/01/29/80099062 ... tormquakes

[Randi]

Tuesday. October 26, 1880.

Meridian to 4 P.M.

Overcast. Wind variable in force and direction. Heavy squalls at increasing intervals, squalls decreasing in force. Between 12 and 2 several squalls of snow and hail. Heavy nimbus clouds and low lying scud driving rapidly to N'd and W'd. Heavy sea and surf. At 1.30 P.M. a shock of earthquake lasting about 20 seconds occurred, after which temperature was raised slightly. Barometer rising.

M.R. Usher. Ensign.

Wednesday. October 27, 1880.

8 P.M. to Midnight.

Cloudy. Light breeze variable in direction. Barometer steady last two hours of watch. At 9.05 a light shock of earthquake lasting 12 seconds occurred. Temperature of water at 11.30 -- 44?F.

J.C. Gillmore. Ensign.

Transcriptions thanks to arboggs.

The factor that I see here in play is the Jamestown is apparently using chain on multiple anchors ("moored head and stern"), and they are under considerable strain of weather. Prior to the 'quake "Starboard mizzen topsail sheet bitt to which chain of quarter anchor is secured, twisted during a heavy squall." Given that you can easily feel the vibrations of an anchor dragging (and could probably tell the difference) I would guess that being well connected to the bottom, with chains taut, would make the ship something of an accidental seismograph capable transmitting "a shock of earthquake" as described, and not mistaken for dragging anchor.