Seaquakes- Actual Shaking, usually felt on vessels due to the arrival of elastic (acoustic) waves through water

Anyone experienced an earthquake at sea?

Yes, as have probably a majority of the experienced mariners here… but how would they know it?

The one I experienced… we thought it was a computer glitch that caused our Dynamic Position system to go haywire (it was showing a very unusual current calculation) we didn’t realize what it was until hours later when reports came in from shore about a tidal wave on the beach.

For mariners who have not experienced or have not heard of a seaquake it seems counterintuitive that they can be felt on a ship.

We felt one while coming around the SW tip of Japan, a few minutes later the SAT-C spit out the tsunami warning (canceled after a short time) very close to our position.

At first the mate thought the ship had run around, but we were in deep water, the chief thought it was heavy cavitation, 1 A/E thought something wrong in the E/R.

This is from the book The Great Alaska Earthquake of 1964:

The term is restricted to actual shaking, usually felt on vessels due to the arrival of elastic (acoustic) waves through water.

If you google “seaquakes” better luck if “books” are searched.

or google “ship damage” and seaquakes

It’s a very distinctive shaking. As if a giant lifted up a huge bowl , that the boat is floating in, and started shaking it side to side.

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Seaquakes - The actual shaking, usually felt on vessels.

That’s a good definition, I’m going to use it.

The effects of a seaquake, as a natural phenomenon, and their influence on ship constructions were studied by the renown geophysicists B. Gutenberg and A. Zieberg (Richter 1963).

Butenberg and Zieberg defined seaquakes as the shaking felt on ships, regardless if the earthquake was on land or under the sea.

Later definitions use seaquake to mean an earthquake under the sea, those can just be called undersea earthquakes. Worse still, some places confuse seaquakes with tsunami, not the same thing at all.

The site CruiseCritc is clueless: What happens on board during an earthquake?

This should be linked to the F’n Yachters thread.


I experienced a seaquake off the coast of Puerto Rico that almost sank us. Ever since, I’ve been researching the effects these events have on diving whales. Most of my work in progress can be found at [Deafwhale Society] (

Seaquake waves are called t-phase waves by scientists. They are very dangerous to submarines with defective welding, In fact, I am convinced beyond a shadow of doubt that seaquake shocks knocked the starboard diving plane off the USS Scorpion in 1968. The plane washed back into the propeller and broke the shaft. The helpless Scorpion went down like a huge boulder. No hope for the crew. The bad part is the US Navy knew the Scorpion had many cracks and defective welds. They just didn’t know how to weld HY80 steel in the 1950s. And they didn’t have trained welders. For this reason, the navies of the world really don’t want folks to know too much about the danger of seaquakes. But they did published articles a few decades ago. Below are hundreds of articles for you to enjoy:

articles on seaquakes, ships, submarines, and whales

By the way, you could not get me aboard a new natgas tanker for a million dollars. I wonder how dangerous compressed nat gas is during a potent seaquake?

I would love to hear from anyone who has experienced a seaquake. All information would be held in the utmost confidence! There are a lot vessels owner that do not want anyone to know their vessels were hit by a seaquake. Such facts would destroy resale value!

I would also like to post (with permission) information that could help seamen identify whales injured by seaquakes. I would also like to comment about the recent assault on ships that hit whales by accident. Governments are horrible wrong to blame the death of whales on ship traffic. The shipping industry needs to fight back! I will post with permission.

Captain David Williams

What happens to the vessel? Is it like a slow vibration or shaking? Are there any areas in the world where this happens more often?

I read somewhere that underwater earthquakes can create incredible geometric patterns with bio-luminescent life on the surface, there have been numerous reports of this.

I experienced earthquakes in the Aleutians. No Tsunami or noticeable waves or changes in sea level. It felt as described above. No damage.

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What did the crew think was happening at the time? I’ve heard a couple stories (maybe two stories about the same event). The engineers thought the engine was tearing apart and the mate though the anchor had let go and run out.

Quakes are common enough in Alaska that everyone knew what was happing right away. Most are fairly mild —- Tremblers.

The only violent quakes I can recall were at Atka. We were supporting a construction project. One of the nearby volcanos, can’t remember which one, was active and there were warnings that earthquakes were to be expected and tsunamis were possible.

As most people in Alaska know, if a Tsunami occurs it does ten times more damage than the earthquake.

The first quake was quite exciting, but we were expecting it. We had to get underway so that we would not be caught near shore in case a Tsunami was coming. The quakes and aftershocks happened quite a few times over a week. Each time we got underway, but within an hour there would be a broadcast saying no Tsunami detected.

That makes sense, I was wondering why your story was not like the others.

We were in Dutch, must have been 1985, alongside, I was out on deck running the cargo gear. I noticed all the workers on the pier running away. I looked at my watch to see the time because my first thought was that the workers were going to lunch, even though running to lunch doesn’t make sense.

I didn’t feel anything (not a seaquake, at least not for us) but later I learned that the workers could see the container cranes swaying.

We were told to get underway, I recall all the fishing boats being able to slip their lines and beating us away from the dock and out of Dutch Harbor . We passed most of them as we cleared Iliuliuk Bay at 14 kts.

We didn’t get far before we got the all clear and came back in.

Yes. I was thinking May1986, but It might have been 1985. I

Could have been1986, I got my license early in 1985 and was on the Snowbird about 2 years.

Google tells me about a magnitude 7.7 earthquake 100km from Atka on May 8th, 1986. There was a big eruption of steam from the Korovin volcano at northeastern Atka 15 days later on May 23, 1986.

Yeah, I found this:


SEATTLE, May 7— A series of earthquakes beneath the sea south of the Aleutian Islands today prompted warnings of tsunamis in Japan, Hawaii, and along the west coast of North America from Alaska to Mexico.

Officials, fearing that a tsunami, an ocean wave generated by the quakes, would cause extensive damage or loss of life, urged people in low-lying coastal areas to leave their homes. About 10,000 people in Hawaii, Alaska, British Columbia, Washington, Oregon and California complied, officials estimated.

But the great wave officials feared apparently did not materialize.

Six-Foot Waves Reported

Waves of 5.8 feet at Adak and of about 6 feet at Queen Charlotte Island in the Inland Passage off British Columbia were the largest reported. The Adak wave occurred soon after the largest temblor was felt. Minimal damage from the quake was reportd at the Naval Air Station there.

The largest of the series of six earthquakes was measured at 7.7 on the Richter scale, a measure of ground motion, the Tsunami Warning Center at Palmer, Alaska, reported. The others ranged is magnitude from 4.4 to 6.0. The quakes occurred over a five-hour period from a subsea point about 100 miles south of Adak, where about 5,000 people live at the naval base.

The most powerful of the series occurred at 2:47 P.M., Alaska Daylight Time, (6:47 P.M. Eastern Daylight Time) and was located at 51.3 degrees north latitude and 174.8 degrees west longitude.

Shortly after the tsunami warning was issued, Coast Guard vessels along the West Coast were ordered to sea and civil defense and other agencies in West Coast states were put on alert.

But at about 6:10 P.M., Alaska Daylight Time, Petty Officer Mark Miller at the Coast Guard air facility at Kodiak reported that a surge ‘‘was supposed to be here six minutes ago and nothing is going on.’’

In Hawaii, at about 6 P.M. (midnight Eastern Daylight Time), a spokesman for the civil defense agency announced that a four-foot wave had moved into the harbor at Haleiwa on the north shore of the island of Oahu. At 7:25 P.M., Civil Defense officials lifted the tsunami warning.

The spokesman cautioned, however, that that further waves might come, and urged residents to remember that ‘‘these are energy driven waves and they have a lot more power than the wind driven waves you’re used to dealing with.’’

Lou Parris, a spokesman for the Coast Guard here, said a wave approaching six feet had been confirmed as pounding against the northern tip of Queen Charlotte Island in the Inland Passage about halfway between Juneau, Alaska, and Vancouver Island.

Surges of three feet and under were reported at Shemya, at the western end of the Aleutian chain, and at Dutch Harbor and Sand Point, about 800 miles southwest of Anchorage. ‘Everybody Had a Good Time’

People in the dozen or so villages across the Aleutian chain, t were urged in radio broadcasts or in warnings by military officials to go to high ground.

The Associated Press reported that at Atka, a village of 93 peole 100 miles east of Adak, the people gathered on a hillside.

‘‘Everybody had a good time,’’ said Greg Golodoff, manager of the village store. ‘‘I had a chance to visit.’’ He said the wave ‘‘was up to the high tide mark, that’s all.’’

All of the Aleutians, a string of islands stretching more than 1,000 miles between the North Pacific and the Bering Sea, were created by volcanoes, and in the past two months three of them have erupted. To the south of the crescent is the Aleutian trench, three miles deep, where scientists theorize the Pacific Ocean floor is being forced under the islands, generating earthquakes and volcanic eruptions.

This process is under way, episodically, along the entire length of the Aleutians as the Pacific floor moves inexorably to the northwest.

Tsunamis are caused by a sudden change in depth of the sea associated with an earthquake. According to Bruce Presgrave of the Colorado center, the extent of damage from a tsunami would depend on the configuration of the sea floor and the coast line the wave strikes. Tsunamis Move Fast

Unlike ordinary waves, tsunamis are only a few inches high as they move across the open sea. But they are very broad and travel at extremely high velocity, crossing an ocean in a matter of hours. A wave that is virtually unobservable in the open sea however, can pile up on a shallow coast line and rise even higher in a tapering bay.

Special attention has focused in Alaska on the Shumagin Islands, far to the East of yesterday’s quake, because no quake has occurred in that sector in many years, and one was considered overdue.

This is one reason Alaskan mariners do not implicitly trust the charts.

Tsunamis are caused by a sudden change in depth of the sea associated with an earthquake

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Don’t confuse a seaquake with a tsunami. If the seafloor moves horizontally during a seaquake, a vessel will not feel much. On the other hand, if the seafloor shifts vertically, the vessel will feel shocks. The intensity of the shocks will depend on the speed of the vertical motion (acceleration) in the seafloor and the depth of the hypocenter below the rock/water interface. The more shallow the focal point, the greater the danger. A seaman can experience 20 seaquakes and never really be frighten. On the other hand, a seaman might experience only one event and lose his life. Many vessels that mysterious disappear are victims of seaquakes. There is a special danger with seismic seafloor vibrations match the frequency of free vibrations of the ship. In such a case, resonance is established between the dancing seafloor and the ship on natural harmonics and the vessel can easily shake itself to pieces similar to how an opera singers voice can shatter a wine glass.

I experienced one off the Queen Charlottes while on the 00-04 watch on a diesel electric plant. I didn’t notice the first couple of tremors as I was out on a round of the machinery space. The 2/m called down to ask about the vibrations he had started feeling on the bridge that were coming and going. I still hadn’t felt anything but as we were talking the control room began shaking and there was a very deep and low rumbling sound that was distinct from the sounds of the machinery. It was a very uneasy feeling. It lasted for what felt like 45 seconds or so. We were still trying to figure out what was going on when the 2/m got a call from a nearby steam ship asking if we had felt anything. Very soon after the bridge printer started spitting out a tsunami warning. There was no damage to the ship but it did wake people who were sleeping.

Looking back through my discharge papers and from what I remember of the ship’s schedule, I’m almost certain that it was one of the aftershocks from this quake:

Speaking of seaquakes …

I was in the engine room of a 50m boat at the dock in Ballard when the 2001 Nisqually earthquake occurred. It was a quick series of strong and rapid “bang bang” shocks that felt like we had been hit by another boat followed by a slight roll.