Why is this thread 10 pages long? It just makes us look silly, here at ATS.
It was the 6.5 earthquake.
P-waves don't take hours to first be registered on seismographs around the world. (Although it can take that long for things to stop bouncing
around.) The p-wave travel times are publicly accessible. They would have started everywhere around the world by 16:37. Here they are:
Lima, Peru 6.72 1:46.5 16:20:15.5 P
San Juan, Puerto Rico 26.92 4:55.9 16:23:24.9 P
Miami, Florida 34.65 6:01.9 16:24:30.9 P
Mexico City, Mexico 38.54 6:33.7 16:25:02.7 P
Brownsville, Texas 42.13 7:02.3 16:25:31.2 P
Knoxville, Tennessee 45.61 7:29.1 16:25:58.1 P
Washington, D.C. 46.99 7:39.5 16:26:08.5 P
Philadelphia, Pennsylvania 47.89 7:46.2 16:26:15.2 P
New York, New York 48.59 7:51.4 16:26:20.4 P
St. Louis, Missouri 49.64 7:59.1 16:26:28.1 P
Boston, Massachusetts 50.15 8:02.9 16:26:31.9 P
Wichita, Kansas 51.55 8:13.0 16:26:42.0 P
Bangor, Maine 52.68 8:21.1 16:26:50.1 P
Ottawa, Canada 53.36 8:26.0 16:26:55.0 P
Albuquerque, New Mexico 54.20 8:31.8 16:27:00.8 P
Phoenix, Arizona 56.42 8:47.3 16:27:16.3 P
Golden, Colorado 56.85 8:50.2 16:27:19.2 P
Duluth, Minnesota 57.57 8:55.1 16:27:24.1 P
Palmer Station, Antarctica 59.84 9:10.3 16:27:39.3 P
Los Angeles, California 60.89 9:17.2 16:27:46.2 P
San Francisco, California 65.77 9:48.4 16:28:17.4 P
Seattle, Washington 71.37 10:22.1 16:28:51.1 P
London, England 84.92 11:34.5 16:30:03.5 P
Honolulu, Hawaii 89.44 11:55.7 16:30:24.7 P
Bergen, Norway 90.55 12:00.8 16:30:29.8 P
Rome, Italy 90.94 12:02.6 16:30:31.6 P
Anchorage, Alaska 91.44 12:04.9 16:30:33.9 P
Wellington, New Zealand 101.99 12:52.1 16:31:21.1 Pdiff
Moscow, Russia 107.45 13:16.3 16:31:45.3 Pdiff
Nairobi, Kenya 108.03 13:18.9 16:31:47.9 Pdiff
Brisbane, Australia 124.24 14:30.8 16:32:59.8 Pdiff
Tokyo, Japan 140.34 15:42.3 16:34:11.3 Pdiff
Agana, Guam 143.95 15:58.3 16:34:27.3 Pdiff
Beijing, China 147.49 18:36.4 16:37:05.4 PKPdf
Kathmandu, Nepal 150.70 18:41.7 16:37:10.7 PKPdf
When you see something like this, first of all check a cleaner seismograph. The ones accessible at the OP's link have a pretty primitive display.
Try one of the ones at Yellowstone:
(Horse Butte)
www.seis.utah.edu...
then, go to the global earthquake list and look for a quake of any substantial size just before the anomaly:
earthquake.usgs.gov...
Oh, I see a 6.5 earthquake in Brazil, registering at 16:18 UTC. Let me check the P-wave times. OK, that explains it. Done! You Are Not Doomed.
If you don't want to do that, cool, but stop ignoring the people who are telling you what it was.