TSUNAMI: A NEW CONCERN FOR RESPONDERS

BY LARRY COLLINS

Despite their potential for huge life losses and the destruction of coastal cities, tsunamis remain a little-understood phenomenon to many emergency responders. Tsunamis (sometimes called seismic sea waves) are usually low on the priority list of public safety agencies along both coasts, even in some zones long identified as vulnerable.

But those priorities may change in certain regions as emerging research and experience indicate many cities on the West Coast are vulnerable to “near-source” tsunamis that can wipe out large coastal tracts and kill tens of thousands of people within minutes of precipitating events such as offshore (and even on-shore) earthquakes and underwater landslides. For firefighters and chief officers, the information indicates a new 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 conduct other post-earthquake emergency operations. The danger may come in the form of one of more seismic sea waves 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.

TSUNAMI DANGERS

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), “tidal waves” have been relegated to the realm of the improbable and therefore are unworthy of serious consideration. Many officials are under the mistaken impression that 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 like those generated by large storms and other typical oceanographic and weather conditions. Tsunamis are very different (and hence far more dangerous) with respect to their inertia and ability to sweep ashore from great distances.

Although it’s true that tsunamis may be quite tall, the true danger is related to the mass of energy that propels them through the ocean at great speeds. This thrust is generally the result of significant vertical movement of large blocks of the earth’s crust during earthquakes, 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 pick up ships and large buildings and carry them inland. Certain topographic features of coastal zones (such as bays, inlets, and river mouths) can magnify this effect.

NEAR-SOURCE TSUNAMIS

With the exception of places like Alaska, Washington state, and Oregon—places long known to be at risk from near-source tsunamis originating in the subduction zones on which these areas lie—the threat of tsunamis in most U.S. coastal areas has traditionally been considered to originate with distant sources, thereby allowing hours of warning. In fact, the National Tsunami Warning Center was established to provide timely warning of such far-source events.

Likewise, fire/rescue officials in places like Southern California have long been assured that the threat of tsunamis originates from distant sources such as 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.

But now that view is changing, partly because of the newly discovered threat of near-source tsunamis in California (including the unlikely location of Lake Tahoe, hundreds of miles from any modern ocean coastlines).1 Scientists now say that Southern California can suffer near-source tsunamis within minutes of a local earthquake, with the most densely populated beach communities as the main targets. To understand why near-source tsunamis should be of serious concern to fire/rescue authorities, one need look no further than the experience of Turkey.

LAND SUBSIDENCE, WAVES, AND RESPONSE

A rarely discussed effect of the deadly 1999 earthquake that struck the Izmir region of Turkey was the devastation resulting from the incursion of the Sea of Mara Mara, which left portions of several coastal cities under water, literally sunk beneath the waves. Dramatic land subsidence accompanied by large tsunamis occurred during the 7.4 Richter Scale main shock, with walls of water washing across city streets just as some people emerged from their homes in the predawn darkness to escape from collapsed or damaged buildings.

The unsettled sea rushed inland like a flash flood in the dark. Walls of black water, reaching up to two stories in height, carried automobiles, boats, and debris. As each wave receded, buildings and people (some still inside their automobiles—including at least two police officers) were washed into the sea. It was a cruel blow, piling more misery on 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 firefighters and rescue teams access to affected areas. Victims who might otherwise have survived until rescuers reached them simply drowned as seawater swept into quake-damaged buildings. Rescue divers discovered some (including those still in their vehicles) on the sea floor in the days following the quake. It was mute evidence of the power of tsunamis and related events. But it could also happen in the United States, say many experts.

HIDDEN THRUST FAULTS SURPRISE EXPERTS

West Coast emergency services have long recognized the potential for tele-tsunamis, which are those generated by distant earthquakes. A few hours after the 1964 Good Friday earthquake struck Fairbanks, Alaska, remnants of quake-generated tsunamis killed people in Crescent City in Northern California and caused serious property damage in parts of Southern California. Throughout the geologic history of the Americas, the West Coast has been the site of tsunamis originating from earthquakes and underwater landslides in distant spots on the planet.

In this respect, Southern California differs markedly from the Pacific Northwest, where subduction zones2 have shaped the rugged coastline and spawned giant volcanoes, and where the potential for locally generated tsunamis, which may strike within minutes of an earthquake, is a generally recognized hazard. In Southern California, seismologists and geologists for decades were under the mistaken impression that all earthquake faults there were of the “strike-slip” variety. Strike-slip faults aren’t directly associated with tsunamis because when they rupture, one side moves past the other sideways. This is in contrast to “thrust faults,” in which one side is suddenly thrust upward in relation to the other when they rupture. When this happens below the sea, tsunamis can be generated. However, thrust faults were not thought to exist in Southern California until very recently.

Thus, Southern Californians generally assumed that locally generated tsunamis3 were not an 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, it appears this view was mistaken.

The 1992 Cape Mendocino earthquake surprised seismologists by generating a small tsunami that struck the Northern California coastline within minutes. This was a region thought to be invulnerable to near-source tsunamis. Even though the tsunami was rather small, the event 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 occurred that was far larger and more troubling—the disastrous 1994 Northridge earthquake. This quake, which killed nearly 70 people, originated in a previously unidentified “hidden thrust fault.” Scientists couldn’t find the ground fault rupture from Northridge and surmised that the event occurred on a thrust fault deep beneath the surface, which was eventually verified. Including the Coalinga (Central California) earthquake in the early 1980s, 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 are out there, and how many are hidden below the ocean?

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.

Scientists now recognize that these faults are capable of generating large tsunamis that can make landfall within minutes or even seconds. In the case of Santa Barbara, in which computer modeling has been completed by a team headed by Dr. Costas Synolakis of the University of Southern California’s (USC) School of Engineering, localized tsunamis approaching 36 feet high are considered 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 (OES)] found evidence of a very large crack in the offshore coastal shelf, which appears capable of separating. This would result in 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

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 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/USC studies indicate that such critical areas as 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. 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 property damage. 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 for decades have assured emergency planners that locally generated tsunamis are not a credible threat. As a result of such assurances, few Southern California municipalities have developed warning systems or emergency response plans for locally generated tsunamis.

Consider Marina Del Rey, one of the largest private yacht basins on the West Coast, nestled between Santa Monica and Los Angeles International Airport. 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. The study is not yet complete, but it is evident that such an event would almost certainly cause a large loss of life.

A six-foot tsunami striking Marina Del Rey would carry with it boats, yachts, and floating docks as it moved across the water. On striking the inland edge of the Marina, the wave would come ashore, adding automobiles and buildings to its debris load as it moves 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 in 1998. 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 15 to 20 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 man-made waterways are particularly vulnerable to tsunami action because they tend to propagate large waves farther inland. Low, flat areas are also a natural target. For this reason, some of the most valuable property on the West Coast may be Ground Zero for deadly tsunamis.

Consider a large tsunami striking land, picking 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 similar to that of multiple flash floods that completely (and repeatedly) reverse course. In the aftermath of a catastrophic earthquake, such an event may severely intensify 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 such as roads and bridges, is probable in some scenarios. The potential for trapped live victims who will need specialized extrication resources is significant.

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

One option is to establish multidiscipline 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 is also a need for realistic warning systems that include not only signs posted in multiple languages but also 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 where near-source tsunamis may occur. A tsunami plan for a fire department in a potential impact zone might begin with the recognition that strong shaking in coastal areas should cause firefighters to immediately abandon fire stations, evacuate to high ground or to an area that is a safe distance from the coast (based, in part, on tsunami impact and inundation maps), and 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, the dispatch center might issue standard tsunami warnings and evacuation instructions. 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’s committing to potential inundation areas for nonlife-saving operations until the danger of multiple waves has passed (a period of hours, according to some tsunami researchers). There has to be a solid action plan for cases where fires have broken out, where people are trapped in collapsed buildings, and where mass-casualty situations exist 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. It might also include provisions for predeploying resources in anticipation of predicted tsunamis from distant sources.

In an age where managing the consequences of terrorist attacks (some involving weapons of mass destruction) has rightly become the national priority and where hurricanes, floods, and damaging earthquakes are constant concerns, it may be difficult to get worked up about the dangers presented by tsunamis, which clearly are rare 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 loss of firefighters, rescuers, and citizens during a “near-source” tsunami, 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.

Endnotes

1. 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 more than 30 feet high. Such an event might kill thousands of people and wipe out the dozens of towns that surround the lake.

2. Subduction zones are tectonic plate boundaries where one plate dives beneath another. When these fault zones rupture, one side is suddenly raised, sometimes in large blocks of land beneath the ocean. This sudden raising of the seabed causes a colossal displacement of the ocean water, which can generate tsunamis so large they can wipe out entire cities. Other side effects of subduction zones include volcanoes created by the friction of the two plates sliding beneath or past one another. The coastal regions of Northern California, Oregon, and Washington sit directly over a major subduction zone, indicated by their trademark volcanoes, rugged coastline that is vulnerable to subsidence and tsunamis, and the fact that these areas have experienced some of the largest earthquakes in history.

3. 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: There is little warning and little time to escape the shoreward-rushing seas that accompany them.

LARRY COLLINS, a member of the County of Los Angeles Fire Department (LACoFD) for 23 years, is a captain, USAR specialist, and paramedic assigned to USAR Company 103. He is a search team manager for the LACoFD’s FEMA/OFDA Urban Search and Rescue (US&R) Task Force and serves as a US&R specialist on the “Red” FEMA US&R Incident Support Team. He is a frequent instructor at FDIC and FDIC West and author of the rescue chapter in The Fire Chief’s Handbook (sixth edition) and of the upcoming book Rescue: A Guide to Urban Search and Technical Rescue (Fire Engineering).

No posts to display