Japan Earthquake: One Month Later

One month after the deadly 9.0 Japanese earthquake, the rescue workers and government took a moment of silence to remember the disaster that leveled portions of northeastern Japan after the quake triggered a large tsunami.

But even after a month, the ground hasn’t stopped shaking. Last week a large 7.4 aftershock triggered another tsunami warning and exactly two hours and thirty minutes after Japan marked the one-month anniversary three strong aftershocks rattled fragile nerves. First, a 6.6 aftershock hit at 5:16 p.m. local time, followed a minute later by a 6.0 and nine minutes after that by a 5.6 aftershock.

Even though the quake was devastating enough, the size and location created a nuclear emergency that still isn’t over. On the one-month anniversary Japanese officials extended the boundary of the evacuation zone around the hobbled Fukushima Daiichi nuclear power plant. Shortly after the quake and radiation leaks began, everyone within a 12-mile radius was evacuated.

The environmental group Greenpeace found high levels of radiation outside the evacuation area last week. Since then it has been pushing for the evacuation zone to be expanded. International pressure is prompting the Japanese government to increase the contamination area to prevent people from eating food that has absorbed radiation. This, the group says, will minimize long term health effects caused by radiation, including cancer years from now.

Greenpeace radiation expert Rianne Teule says it is the only way to safeguard the Japanese people.

While most of the world is rightfully focused on the ongoing nuclear disaster that resulted because of the great quake, some scientists are watching the ground beneath Japan and looking for clues as to why the ground is shaking.

The Tohoku earthquake and tsunami was a giant underwater mega-thrust quake that started almost 20 miles below the ocean’s surface (relatively shallow in seismic terms) when a large amount of pressure that had been building quickly released as the Pacific tectonic plate subducted beneath one of the Japanese plates — scientists are still arguing over which plate.

That seismic event, as geologists call it, created a 310-mile rupture which is very unusual given the nature of the fault line. Generally big quakes are associated with long straight faults but this fault line is not straight and scientists before this quake didn’t think it could generate a quake larger than an 8.5 on the Richter scale.

When the mammoth quake — now known to be one of the top five in recorded history — struck it released a surface energy nearly double that of the 2004 Indonesian earthquake which killed 230,000 people. Although over 25,000 people perished, Japan is the most earthquake-prepared nation. Its early warning system gave people a one-minute head start and surely saved thousands of lives.

Since the quake first struck a month ago, over 900 aftershocks have been felt, including over 60 registering above a 6.0 magnitude and three higher than a 7.0 magnitude.

The initial quake actually pushed Japan’s Honshu island about eight feet closer to North America. 250 miles of Japanese coastline dropped two feet, helping the tsunami that resulted travel further inland. As a result Japan will need to recalibrate its global positioning system to reflect the new topography. The earthquake also shifted the Earth’s axis by ten inches. And that change caused some minor planetary changes.

The sudden redistribution of the Earth’s mass sped up our rotation, which in turn shortened the day by 1.8 microseconds, an imperceptible amount. It also changed the Earth’s axis by a slight margin.

Many geologists are looking at the direct effects of the big quake and a few are a little concerned by what they are finding.

Just a week after the quake, Brian Atwater at the US Geological Survey said it looked like the big quake piled pressure onto adjacent sections of the fault line, adding new strain closer to Tokyo, Japan’s largest city, which houses 35 million people. Since then other seismologists and geologists have agreed that the faults near the part of the Japan Trench that ruptured now have added stress.

But that doesn’t mean that Tokyo is in line for a major quake because of it. While the added fault stress is interesting from a scientific standpoint it shouldn’t raise undue concern.

USGS researcher Susan Hough says, “Big earthquakes don’t cascade like dominoes, bang bang bang. At least not commonly. So I think the maps showing bright red bull’s eyes of increased stress may be more alarming than they should be.”

Ross Stein, another USGS scientist says, “The watchword in Tokyo should be long-term vigilance. Nobody should think this should go away in a few weeks or a few months.” He believes the aftershocks will likely continue for as much as ten years.

But Japan does sit in a seismic bullseye within the ring of fire, a 25,000-mile stretch of earthquake and volcano rich territory. This area which rings the Pacific Ocean is prone to big quakes as the giant Pacific tectonic plate pushes and grinds against smaller plates.

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