The massive tremors and ensuing tsunami that devastated Japan earlier this month was an order of magnitude more destructive than anything that has hit the continental Unites States in historical times. But seismologists say that a similar event could well strike here. In fact, it’s only a matter of time. And compared to Japan, we’re far less prepared to deal with the consequences.
The danger zone is not California. While Los Angeles and San Francisco suffer frequent damaging quakes, they owe their seismic woes to a relatively shallow phenomenon called a slip-strike fault, caused by two tectonic plates sliding against each other. Sendai was a result of something far more dangerous: a so-called subduction zone, a deep-lying discontinuity caused by one plate slowly burying itself under another.
In both cases, earthquakes are caused by the slow building of pressure as the two plates move relative to one another, but remained locked together at the fault line. The strain increases steadily until the fault gives way, releasing the energy in the form of an earthquake. While strike-slip faults are relatively shallow, a subduction fault is deeper and can release a lot more energy. “One of the signatures of this type of fault,” says Mike Blanpied, associate director of the US Geological Survey’s Earthquake Hazards Program, “is that they sit quietly until they create a giant quake.”And by giant, he means monster. The Sendai event contained more than 30 times the energy of the San Francisco Earthquake of 1906.
Only one such region lies within the Lower 48. It lies off the coast of Oregon and Washington and is called the Cascadia Subduction Zone. Today the Northwest seems seismically calm, but in reality the fault could let go again at any moment. In 1700 the subduction zone spawned an earthquake of roughly the same size as the Sendai event, unleashing a tsunami that may have reached 100 feet high. Based on geological evidence, Chris Goldfinger, director of the Active Tectonics and Seafloor Mapping Lab at Oregon State University, believes that in the past similar-sized quakes have happened about every 300 to 350 years – meaning we’re just about due.
To figure out what would happen if a Sendai-scale event struck today, a consortium called the Cascadia Region Earthquake Workgroup (CREW) has drawn up a detailed scenario of how the quake and its ensuing tsunami would affect buildings, transportation, utilities, and emergency services. The report, entitled “Cascadia subduction zone earthquakes: A magnitude 9.0 earthquake scenario,” painted a picture so grim that it read like a bad Michael Bay script. It was pretty hard to believe—until the Sendai quake brought all its horror vividly to life. It can happen.
When it does, it may well run something like this:
Somewhere, a dog starts barking. A hanging lamp begins to sway. The next thing you know, you’re in mid-air and your living room furniture is sliding across the room. You hit the ground and scramble underneath a coffee table as a cabinet tumbles, spilling broken china and shards of glass. The refrigerator topples over and the stove shuffles across the kitchen floor. Across town, bridges and high-rise buildings shudder, buckle, and collapse. The power goes out, and fires break out all across the city. Two minutes later, when the shaking stops, hundreds of buildings have collapsed and thousands are dead.
But the disaster isn’t over. Outside your window, the ocean is draining away from the beach. For a moment a strange silence hangs over the exposed seabed. Then, with a roar, the sea comes galloping in, a wall of frothy whitewater that surges over seaside towns, sweeping away roads and bridges and drowning thousands more. Landslides bury houses and sever mountain roads. In the aftermath, more lives wink out, as victims trapped beneath rubble suffocate or succumb to their injuries. With roads cut and power out, rescue services are all but helpless. Many victims in the quake zone could go days without help from the outside world.
If its imagined scenes of devastation sound a lot like what happened in reality in Japan, that’s no coincidence. Both catastrophes result from the same time of fault rupturing with the same intensity. They have one well-known precedent in the United States. On Good Friday, 1964, Alaska was hit by an epic five-minute-long quake that registered 9.2, making it the most massive ever recorded in North America. On Kodiak Island, land was raised up 30 feet. Elsewhere, whole villages were destroyed as the ground beneath liquefied and sank. Anchorage suffered devastating landslides, and 30 city blocks were damaged or destroyed.
The magnitude of a quake alone tells you little about its effect on a population. The suffering that results is really a function of two things: the intensity of the shaking and the quality of the preparations that have been made. Japan is by far most earthquake-savvy country on the planet. It lavishes millions on research, its building codes are tough, and its people are psychologically ready. Yet despite Japan’s preparations the 9.0 earthquake wreaked havoc on a scale not seen since World War II.
Americans, on the other hand, spend little time thinking about earthquakes, and even less money. We’re just starting to explore technologies that the Japanese have been implementing for decades. One step toward protecting the public, for instance, would be to establish an Earthquake Early Warning (EEW) system. The idea is to detect tremors as a fault begins to slip, and then transmit an alarm signal to population centers on the periphery of the quake zone. Since motion of the quake travels at the speed of sound, and the signal can travel near the speed of light, an efficient system could provide a minute or two of warning—enough time to stop elevators and let passengers off, or for a teacher to shepherd her students under their desks.
Such a system in Japan gave residents of Tokyo more than a minute’s warning that a major temblor was on its way, and may have saved countless lives. For anyone who likes to believe that America stands at the forefront of technology, the sad truth is that we’re still years away from developing such a capability – if indeed we ever succeed.
Right now the USGS is trying to piece together a system that would protect the most vulnerable areas of northern and southern California. Project chief David Oppenheimer says that the system will require the installation of 120 up-to-date seismic monitoring units to provide the necessary density of sensors. In this age of budget cutbacks, the money needed to move forward is in short supply.
Should a magnitude 9.0 earthquake strike the Pacific Northwest tomorrow–and there’s no reason it shouldn’t—the initial damage would in all likelihood be at least as bad as the devastation in Japan, and the aftermath far worse. If there’s a bright side to the Sendai quake, it’s that it might wake up enough concerned citizens to that fact. The first step in being prepared is understanding that the threat exists.