Tsunami Fears and the Closing of U.S. Navy Shipyards

At a time when China’s ship-building capacity is 232 times greater than the U.S.’s, the U.S. Navy closed four of its few dry docks due to ‘seismic risk’

In 1958 an earthquake caused a large rockfall in Lituya Bay, just 1,550 kilometers north of Seattle. The rockfall fell from a height of 914 meters into deep water and caused a splash wave that sheared off pine trees up to a height of 524 meters on the opposing mountainside. People trapped on boats in the bay then watched in horror as a wave of around 30 meters high raced over the bay towards them. One fisherman and his son were on a small boat that was lucky enough to have its anchor chain snapped off by the wave, allowing the boat to ride the wave as it towered over the trees on the shoreline. The boat then slid down the back of the wave where the two had to hang on for dear life as secondary waves sloshed the boat about.

The 1958 Lituya Bay “megatsunami” was not a regular tsunami because it did not form in the open ocean. Instead it formed in what was essentially a lake with only a very small and shallow opening to the sea. The confining geography of lakes allow such landslide-induced waves to grow very tall but they soon run out of steam. If such a landslide fell into the open ocean, the sheer volume of surrounding water would quickly absorb the wave energy and the height of the wave would quickly decrease.

Today, the Seattle area is bracing for a very different wave. Scientists have found that, just 300 kilometers west of Seattle, a tectonic plate called the Juan de Fuca Plate is struggling to slide under the North American Plate. Unlike in northern California, where the massive pressures created by similar tectonic struggles are relieved by small tectonic slips that humans experience as earthquakes, the plates near Seattle do not relieve their tension with small slips. This means that they are bound to release all that tension in one large slip that scientists predict will cause the seabed to jump around 9 meters “or more” upward, causing an oceanic tsunami that would be hundreds of kilometers wide and around 20 meters high, on average.

The mechanism that is currently creating this future tsunami is very similar to the mechanisms that caused the 2004 Indian Ocean tsunami and the 2011 Tohoku tsunami that hit Japan. The U.S. Geological Survey data and the current scientific consensus suggest a 15 to 24 percent likelihood that such an off-shore megaquake will occur in the Pacific Northwest in the next 50 years.

The people of the northwestern U.S. have been made well aware of what is brewing out in the ocean. It was with some trepidation then, that they took in the news that the U.S. Navy had decided to “temporarily suspend submarine docking” in four dry docks in the Puget Sound “following a planned seismic study and expert analysis.” The Navy’s statement published on January 27 said that a recently conducted seismic assessment “identified potential issues associated with the remote possibility of a large-scale earthquake occurring simultaneously with a submarine maintenance availability.” Did the Navy know something that no one else knew?

The shutdowns came at a bad time for the U.S.’s military shipbuilding industry. The sudden closing of four nuclear-certified dry docks complicated the U.S. Navy’s ability to refurbish and decommission nuclear-powered ships and submarines. It left the Navy with fewer dry docks at a time when the submarine force was already strained, as 18 attack submarines fleetwide were in a maintenance period or pierside waiting to enter one when the closures were announced on January 28. This is nearly double the number of subs that the Navy’s schedulers have planned to be sidelined for maintenance.

Just this week, news media reported on leaked data from the Office of Naval Intelligence that the growing gap between the fleet sizes of China and the U.S. is being accelerated by the fact that China’s shipbuilders have a shipbuilding capacity that is 232 times greater than that of U.S. shipbuilders. The news reignited longstanding concerns about the U.S. Navy’s preparedness to sustain its forces and face off against Chinese fleets if China tries to invade Taiwan.

The closure of the four Puget Sound dry docks also exacerbated a crisis that the Navy is experiencing in refurbishing aging Los Angeles-class nuclear submarines to fill the gap created by the fact that the U.S.’s four naval shipyards are not meeting their schedules for delivering new nuclear submarines and warships.

Eighteen days after announcing the closure of the four dry docks, the Navy said it had started doing “seismic mitigation efforts” at two of the docks. These efforts are large-scale construction projects that include drilling deep holes to install anchoring structures in the high and thick walls of the dry docks. The biggest fear of the Navy is that a predicted 9.0-magnitude megaquake would cause liquefaction of the unstable soil around the dry docks’ walls, causing the walls to collapse and damage the multibillion-dollar nuclear submarines. When one looks at the highly protective geography around the Navy’s submarine yards near Seattle, it becomes clear that a large tsunami would not do much damage to the yards or the city, as they are situated in fjord-like waterways that are protected by large peninsulas. The main threat would be from the shaking of the earth and the liquefaction that goes with it.

One of the four affected dry docks did open on May 12, after just over three months of seismic strengthening work. The opening also saw the arrival of the USS Pennsylvania (SSBN 735) nuclear ballistic missile submarine at the dry dock, where it is currently undergoing a six-month refueling and refurbishment process.

Some analysts hinted that the dramatic announcement of dry dock closures could have been partly a political mechanism to convince politicians that the Navy is in trouble and needs more money to solve its huge construction and maintenance issues. Either way, the fact remains that the U.S. is falling behind China in the race to build and maintain warships and submarines.

For the warship part of the equation, falling behind might not be such a bad idea. The CSIS recently ran a number of wargames to see what will happen if China invades Taiwan and the U.S. military is forced to intervene. From those results, the CSIS concluded that the deployment of warships in such a scenario would not be advisable, as modern anti-ship missiles have become too good at destroying surface vessels. The CSIS therefore advised the U.S. Navy and U.S. Air Force to build up a large arsenal of long-range anti-ship missiles like the LRASM and use these to sink the ships of an invading force from very far away. 

Su Tzu-yun (蘇紫雲), a research director at Taiwan’s Institute for National Defense and Security Research (INDSR), told Domino Theory he calculated that it takes on average around 24 months and $1 billion to build a warship, but it only takes a few days and $1 million to build an anti-ship missile. “If you consider that it would require only around five such missiles to sink one enemy ship, then it becomes clear that anti-ship missiles offer a big opportunity for defenders to gain an advantage in terms of spending and military effectiveness.”

Both Taiwan and the U.S. seems to be taking the advice to heart, as both are currently investing big in buying high-tech missiles that can fly for hundreds of kilometers before they find and destroy the warships they were sent to kill. The plan would be to halt an invasion of Taiwan by using thousands of these missiles to cripple a fleet that would have to carry the troops and weaponry needed to take Taiwan by force. Su told Domino Theory that this strategy “will effectively establish an area-denial zone and maximize the deterrence against Chinese amphibious threats — and this would mean there can be no amphibious landing, so it would make no sense for China to go to war.”

Image: U.S. Navy, Public Domain