CFS Press




New Findings On Near-Source Tsunami Hazards and Tele-Tsunamis

by Larry Collins,
L.A. County Fire Department USAR 103 ( lcollins@lacofd.org )

Background:

Despite the potential for huge life losses and the destruction of coastal cities from them, tsunamis remain a little-understood phenomenon to many firefighters and fire/rescue agency leaders.  Tsunamis (sometimes called seismic sea waves) are often low on the priority list of public safety agencies along both coasts, even in some zones long identified as being vulnerable to their effects. 

In nations like Japan , where entire fire departments have nearly been decimated in this century by tsunamis that struck in the night during post-earthquake firefighting and rescue operations, there is widespread appreciation for the lethal effects of these events. The goal of this article to help instill the same appreciation in vulnerable coastal areas, before a tsunami disaster kills large numbers of firefighters and rescuers needlessly…and to highlight new discoveries to encourage fire/rescue agencies in vulnerable areas to develop realistic plans to address this unusual but very lethal hazard.

Emerging research indicates many cities on the West Coast previously thought to be invulnerable to “near-source” tsunamis, are in fact prone to large tsunamis that can wipe out large coastal tracts and kill tens of thousands of people within minutes of  precipitating events like offshore (and even onshore) earthquakes and underwater landslides.  For firefighters and chief officers, the new information indicates a previously unrecognized danger when assessing post-earthquake damage along the coastlines, and while attempting to suppress fire, rescue trapped victims in collapsed structures, treat  the injured, and other post-earthquake emergency operations.  The danger may come in the form of one of more seismic sea waves (sometimes that second or third tsunami is larger than the first) that can strike with little warning, within minutes of an earthquake or underwater landslide, and take the lives of firefighters and rescuers sent into damaged areas.

On the Danger of Tsunamis

The closest many of us will come to actually experiencing a tsunami is the movie screen. To the casual observer, and to many otherwise well-informed public safety officials, so-called “tidal waves” (a mismatched term often used to describe tsunamis) have been relegated to the realm of the improbable, and therefore unworthy of serious consideration.  Many officials mistakenly assume they will have hours to evacuate threatened populations to high ground.  This, unfortunately, is not always true.

Contrary to some common perceptions, seismic sea waves aren’t simply “large waves” of the sort generated by large storms and other typical oceanographic and weather conditions.  To the contrary, tsunamis are very different (and hence far more dangerous) with respect to their inertia and their ability to sweep ashore for great distances.  While it’s true that tsunamis may be quite large in height, the true danger is related to the mass of energy that propels them through the ocean at great speeds.  This “thrust” is generally caused by significant vertical movement of large blocks of the earth’s crust during earthquakes, or by the occurrence of large underwater landslides, or both.  When such a mass of waterborne energy strikes the coast, it may suddenly raise the level of the sea and drive walls of water far inland, creating a sort of flash flood that can pickup ships and large buildings and carry them inland.  This effect can be multiplied by certain topographic features of coastal zones such as bays, inlets, and river mouths. 

Misunderstood Threat of “Near Source” Tsunamis

With the exception of Alaska , Washington State , Oregon , and Northern California--places long known to be at risk from near-source tsunamis originating in the subduction zones upon which they lie[1]—the threat of tsunamis in most U.S. coastal areas was traditionally considered to originate with distant sources, thereby providing hours of warning. In fact, the National Tsunami Warning Center was established to provide timely warning of such far-source events, and state and local officials have developed elaborate evacuation plans for these far-source events. 

Likewise, fire/rescue officials in Southern California have long been assured that the threat of tsunamis there rests with distant sources like Hawaii , Peru , Japan , and the Aleutian Islands .  The low incidence of damaging tsunamis during the past century has contributed to a false sense of security in Southern California .  Consequently there has been little urgency to develop elaborate tsunami evacuation and response plans for near-source events, and this can be a devastating oversight in the event of a near-source tsunami.

 For example, current fire department plans in Southern California call for fire/rescue units to respond into their jurisdictional areas to conduct “windshield surveys”, rapid visual and physical assessments of damage levels and major problems (or lack thereof) conducted while these units roll “Code R” through the streets on pre-determined routes to check the status of the most obvious life-loss hazards.  Fire/rescue resources will be moved into heavily damaged areas along the coast once it’s determined that these places are in the greatest need of firefighting, EMS , haz mat, and USAR assistance.  This places fire/rescue personnel in immediate danger in the event of a near-source tsunami that catches them by surprise by striking while the early and most dangerous phase of post-earthquake operations take place.  The danger is that fire departments and rescue teams responding to fires, collapses, casualties, and hazardous materials releases in quake-damaged coastal zones may be wiped out by surprise tsunamis. 

This exact phenomena occurred when a Japanese Island was struck by a major earthquake in the late 1990’s.  As residents evacuated the coastline for high ground in the dark of night, the city lit up with flames from various quake-spawned fires.  As residents and film crews watched in disbelief from the hills, a black wave of water swept into the city below, destroying burning buildings and fire engines alike.  Several more tsunamis followed the first, wiping out large sections of the city.

But now that approach to post-earthquake response and damage assessment must be reconsidered because of the newly-discovered threat of near-source tsunamis along the middle and southern California coasts (and yet another surprise location:  Lake Tahoe, high in the Sierra Nevada Mountains, more than one hundred and fifty miles from the ocean)[2].  To understand why near-source tsunamis should be of serious concern to fire/rescue authorities, one need look no further than the history-drenched nation of Turkey .

1999 Turkish Quake Response Complicated by Land Subsidence and Tsunami-Like Devastation

A rarely-discussed effect of the deadly earthquake that struck the Izmir region of Turkey in 1998 was the devastation caused by incursion of the Sea of Marramar , which left  portions of several coastal cities under water, quite literally sunk beneath the waves.  Dramatic land subsidence accompanied by large tsunamis occurred during the 7.4 main shock, walls of water washing across city streets just as some people emerged from their homes in the pre-dawn darkness to escape collapsed or damaged buildings.

The unsettled sea rushed inland like a flash flood in the dark. Walls of black water carried automobiles, boats, and debris, reaching up to two stories in height.  As each wave receded, buildings, and people (some—including at least two police officers—still inside their automobiles) were washed into the sea.  It was a cruel blow, piling more misery upon a population that had just been struck by one of the worst natural calamities of the century. 

The land subsidence and waves complicated search and rescue operations by denying or delaying access to fire fighters and rescue teams.  Victims who might otherwise have survived until rescue teams reached them, simply drowned as seawater swept into quake-damaged buildings.  Some (including those in vehicles that sank with the land) were discovered on the sea floor by rescue divers in the days following the quake.  It was mute evidence of the power of tsunami-related events. But could it happen in the United States Yes, say many experts.

Newly Discovered Tsunami Problem Shakes Up Southern California

The potential for both tele-tsunamis and near-source tsumanis along the northern reaches of the West Coast has long been recognized.  A few hours after the 1964 Good Friday earthquake struck Fairbanks (Alaska ), remnants of quake-generated tsunamis killed people in Crescent City (Northern California), and caused serious property damage in parts of Southern California .  Throughout geologic history of the Americas , the northern West Coast has been the site of tsunamis originating from earthquakes and underwater landslides in distant spots on the planet, as well as in its own back yard. 

In contrast, seismologists and geologists were for decades under the mistaken impression that earthquake faults in middle and southern California were of the “strike-slip” variety.[3] 

Thus, Southern Californians generally assumed that locally generated tsunamis[4] were a non-issue because the conditions precipitating seismic sea waves had never been found south of the Cascadia region. Until recently, that remained the mantra of many seismologists and earth scientists.  Now, based on emerging research, it appears this view was mistaken (and perhaps over-optimistic).

In 1992 the Cape Mendocino earthquake surprised seismologists by generating a small tsunami that struck the Northern California coastline within minutes of the quake.  It was the first near-source tsunami to be detected South of the Oregon border.  This was a region thought to be invulnerable to near-source tsunamis.  Even though the tsunami was rather small, it indicated the potential for very large tsunamis to strike the coastline within minutes under certain conditions.  The Cape Mendocino event prompted a reevaluation of near-source tsunami hazards in California , one that has yielded surprising results. 

However, before the Cape Mendocino quake studies could be completed, another surprise—this one far larger and more troubling—occurred in the form of the disastrous Northridge earthquake in 1994.  The Northridge quake, which killed nearly 70 people, had its origins in a previously unidentified “hidden thrust fault”.  Scientists couldn’t find the ground fault rupture from Northridge, and began to surmise that the event occurred on a thrust fault deep beneath the surface.  This was eventually verified.  Including the Coalinga ( Central California ) earthquake in the early 1980’s, the state had suffered two damaging quakes on previously unidentified thrust faults.  It was clear that there was a new danger afoot:  If two deadly quakes occurred on hidden thrust faults within a decade, how many other hidden faults were out there? 

Armed with this question, scientists began a quest to quantify the threat posed by thrust faults (hidden and otherwise).  In the intervening years, a number of  previously unknown thrust faults have been identified in California .  Most disturbing, a number of them have been found beneath the waters of the Pacific, off the shores of Los Angeles, Ventura, and Santa Barbara Counties

It’s now recognized by scientists that these faults are capable of generating large tsunamis that can make landfall within minutes or even seconds.  In the case of Santa Barbara , where computer modeling has been completed by a team headed by Doctor Costas Synolakis of the University of Southern California ’s School of Engineering , localized tsunamis approaching 36 feet high are considered to be a possibility.

Researchers have also discovered evidence that large underwater landslides in deep offshore canyons pose a major tsunami risk even before earthquakes are factored in.  Evidence of past tsunamis from this cause have been found from Santa Barbara to Long Beach and Orange County .  The recent Santa Barbara studies (commissioned by the California Office of Emergency Services, or OES) found evidence of a very large crack in the offshore coastal shelf, which appears capable of separating to cause a huge underwater landslide, which in turn would generate large tsunamis that could strike the coastline within seconds or minutes.

As new evidence continues to be uncovered, it’s fast becoming clear that the previously-held assumptions were false.  As a result, yet another hazard is being added to the list of things for which fire/rescue agencies must be prepared:  Devastation of densely-populated coastal zones by large tsunamis striking with little or no warning, sometimes in the immediate aftermath of a catastrophic earthquake.

New Theories About Tsunami Threat

New theories hold that populated coastal areas of Los Angeles County and other parts of Southern California are at moderate to high risk from large tsunamis generated by local earthquakes, as well as from local underwater landslides.  According to the Doctor Synolakis’ team and other  researchers, the potential for heavy damage and loss of life from these events is significant.  Perhaps most disturbing are new findings that local offshore faults are capable of generating large tsunamis that can strike the coast of Los Angeles County within as little as a few minutes, leaving little time for warnings or evacuation. 

The OES/U.S.C. studies indicate that places like critical areas like Marina Del Rey, Malibu , Long Beach , and other densely populated coastal zones are at extreme risk for heavy damage and life loss in the event of tsunamis.  Professor Synolakis and his associates have determined that even moderate-sized tsunamis can propagate far into Marina Del Rey, up Ballona Creek, and up Malibu Creek  (via Malibu Lagoon and directly through parts of Malibu Colony).  They have uncovered evidence that these and other vulnerable coastal sites can suffer huge loss of life and damage to property.  The message for fire/rescue personnel is clear:   If tsunamis are preceded by earthquakes that cause fires, structural collapses, haz mat releases, and injuries along the coast, emergency responders will be exposed to significant hazards that they may not anticipate. 

This is surprising information in Southern California , where scientists have for decades assured emergency planners that locally-generated Tsunamis are not a credible threat.  As a result of years of assurances that tsunamis were low-level risks, few Southern California municipalities have developed warning systems or emergency response plans for locally-generated tsunamis.[5]

Consider the example of Marina Del Rey, one of the largest private yacht basins on the West Coast, nestled between Santa Monica and Los Angeles International Airport .   Professor Synolakis’s current studies demonstrate that a large portion of this coastal community may be inundated by even a “moderate” six-foot tsunami and sea rise.  While the study is not yet complete, it is evident that such an event would almost certainly cause a large loss of life. 

A 6-foot tsunami striking Marina Del Rey would carry with it boats, yachts, and floating docks as it moved across the water.  Upon striking the inland edge of the Marina , the wave would come ashore, adding automobiles and buildings to its debris load as it moved onto land.  Part of the wave would run nearly one mile up Ballona Creek, causing further damage in adjacent neighborhoods. 

Although smaller in size and power, such an event would not be entirely unlike the tsunami that struck Papua New Guinea several days ago.  As in the New Guinea event, Marina Del Rey could be the target of multiple waves, some larger than the first, that could endanger rescuers for fifteen to twenty minutes.  Aftershocks could result in repeated tsunamis for hours after the main shock.

According to several researchers, similar effects could occur at coastal inlets and tributaries like Malibu Creek and other populated coastal zones.  River inlets, creek drainages, swamps, marinas, and manmade waterways are particularly vulnerable to tsunami action because they tend to propagate large waves further inland.  Low, flat areas are also a natural target.  For this reason, some of the most most valuable property on the West Coast may be ground zero for deadly tsunamis.

Consider a large tsunami striking land, pickup up all manner of debris (including boats, automobiles, trees, floating docks, and people) as it moves inland.  The first wave is likely to be followed by others, some of which may be much larger than the pilot wave.  As the waves subside, equally destructive events can occur when the water rushes back toward the ocean, carrying homes, cars, boats, and other debris.  For victims caught in the inundation zone, the overall effect of the incoming and outgoing waves is not dissimilar to that of multiple flash floods that completely (and repeatedly) reverse course.  In the aftermath of a catastrophic earthquake, such an event may severely magnify the search, firefighting, and rescue problems.

Emergency Services Impact:

Post-tsunami search and rescue operations are likely to be difficult and dangerous, possibly requiring the use of swiftwater rescue teams and task forces, rescue divers, helicopters, rescue boats, and other special resources.  Extensive damage to fire department and other municipal structures, as well as infrastructure like roads and bridges, is probable in some scenarios.  The potential for live victims to be trapped, requiring specialized extrication resources, is significant. 

Combined with the other land-based effects that typically occur during damaging quakes (i.e. collapsed buildings, freeway overpasses and dams; multiple fires; haz mat releases, etc),  large tsunamis striking the coast for period ranging from minutes to hours (24 hours in some estimates) would clearly impede the ability of fire/rescue agencies to cope with the disaster.

Planning and Preparations

Considering the steady stream of warnings from seismologists about the potential for damaging earthquakes in the coming years, and the increasing body of knowledge that indicates significant local and distant-source threats, it can be argued that this issue is worthy of immediate attention.  With preparation, fire departments and other public safety agencies have the means to devise effective Tsunami Warning, Evacuation, and Search and Rescue Plans that will serve the public and safety employees well when the next tsunami event occurs. 

One option is to establish multi-discipline working groups to address this issue at the appropriate levels of government.  Fire/rescue agencies in potential tsunami impact zones should seek technical advice from recognized experts who can accurately define the hazards that need to be addressed.

There is a need to develop effective public education programs to raise awareness about the danger from near-source tsunamis as well as far-source events.  There’s a need for realistic warning systems that include not only signs posted in multiple languages, but implementation of audible warning systems (i.e. sirens along endangered coastal zones) that conform to recognized standards.  Such systems are now in place along the coasts of Oregon, Washington state, Hawaii , and other vulnerable U.S. coastal zones.

There’s a need to develop new strategies for fire departments and other public safety agencies within the affected areas of Southern California , as well as anywhere else that near-source tsunamis are possible.  A tsunami plan for a fire department in the potential impact zone might begin with the recognition that strong shaking in coastal areas should cause fire fighters to immediately abandon fire stations and evacuate to high ground or to a safe distance from the coast (based, in part, on tsunami impact and inundation maps), and to initiate immediate public evacuation until the danger of a tsunami is ruled out.

Such a plan should direct the local dispatch center to immediately check with authorities to determine whether the quake's epicenter is offshore, and to immediately transmit epicenter information to field units so they can react appropriately.  If the epicenter is reported to be offshore, there might be standard tsunami warnings and evacuation instructions to be issued by the dispatch center. But even if the quake is centered onshore, the potential for tsunamis resulting from underwater landslides should be recognized.

Tsunami plans should include appropriate cautions against personnel against committing themselves to potential inundation areas—-until the danger of multiple waves has passed (a period of hours, according to some tsunami researchers).  This will clearly cause a conflict in cases where fires have broken out, people are trapped in collapsed buildings, and mass casualty situations occur within potential tsunami impact zones.  The plan should take these factors into account and provide reasonable guidelines for personnel faced with such a dilemma. 

The tsunami plan should recognize the advantage of using helicopters, inflatable rescue boats, and other special resources to conduct search and rescue in the wake of a tsunami event.  It might also include provisions for pre-deploying resources in anticipation of predicted tsunamis from distant sources.

Conclusion

In an age where managing the consequences of terrorist attacks (some involving weapons of mass destruction) have rightly become the national priority, and where hurricanes, floods, and damaging earthquakes are a constant concern, it may be difficult to get worked up about the danger presented by tsunamis, which are clearly a rare event in most coastal zones.  Nevertheless, the potential life loss (including the loss of many firefighters and rescuers during post-earthquake and post-tsunami emergency operations) can no longer be denied in places recently identified as being vulnerable to “near-source” tsunamis. 

Armed with this knowledge about the potential to lose firefighters, rescuers, and citizens during a “near-source” tsunami event, it’s incumbent on local fire department officials and other decision makers to develop a rational response plan that takes into account the need to warn and evacuate the public, to provide reasonable guidelines for firefighters and rescuers assigned to tsunami-vulnerable coastal zones, and to take advantage of the research being done by experts who can help quantify the actual risks.

Footnotes:


[1] It is now known that parts of the coast of Alaska and Washington have dropped as much as thirty feet in an instant during historic earthquakes related to these subduction zones. Scientists have concluded that the areas around Seattle and other densely populated  coastal zones are vulnerable to this type of geologic effect, which would flood the land with a sudden and massive surge of ocean water filling the newly-lowered landscape.  Although this is not a tsunami in the traditional sense, the effects would be equally devastating (if not worse).  In addition to this risk, the Alaska and Washing state coastlines are also prone to “traditional” near-source and far-source tsunamis.

[2] Recently scientists announced the discovery of two thrust faults that run the length of the bottom of Lake Tahoe .  They estimate that an earthquake on either fault may cause tsunami-like waves exceeding thirty feet in height.  Such an event might kill thousands of people and wipe out dozens of towns that ring the lake.

[3] Generally speaking, strike-slip faults aren’t directly associated with tsunamis because when they rupture one side moves past the other “sideways”, without a significant vertical component.  This is the opposite of  “thrust faults” where one side is suddenly thrust upward in relation to the other when they rupture (almost assuredly generating one or more tsunamis in the process). 

[4]. Because they’re caused by events close to land (and because they travel at the speed of a jet airplane), near-source tsunamis are especially dangerous because there is little warning and little time to escape the shoreward-rushing seas that accompany them.

[5] The Ventura County ( California ) Fire Department has for two decades kept a tsunami response plan in effect, and the Lifeguard Division of the County of Los Angeles Fire Department has a plan for  distant-source tsunamis, which are generally preceded by hours with warnings from the Pacific Tsunami Warning Center .

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