The myth and reality of the Japanese earthquake 日本大地震的神秘与真相
BACK in January, Japanese seismologists warnedthat the tectonic plates colliding beneath the PacificOcean off the north-east coast of Japan were poisedto slip catastrophically. By their reckoning, there wasa 99% chance of an earthquake of magnitude 8.0occurring off the Miyagi coast, and a 90% chance ofone off Ibaraki prefecture, within the next 30 years.They were surprised only by the sheer size of the magnitude 9.0 monster that was unleashedwhen the plates at last let go on March 11th.
早在今年一月的时候,日本地震学家就曾警告说太平洋洋底日本东北海岸下的板块相互冲撞会导致造成倾斜、引起灾难。根据他们的估计,30年内,宫城县海岸附近发生8.0级大地震的可能性为99%,而茨城县海岸附近的几率则为90%。3月11日板块终于释放能量、发生9.0级强震,地震学家仅仅惊讶震级如此之高。
It seems that, on occasions, the rupture along this particular type of reverse fault can jump acrossgaps and other boundaries along the fissure, linking up with other parts of the fault to extendthe breach alarmingly. The traditional fault-segmentation model used in seismology does notallow for this. But on that fateful Friday, when the North American plate slid over the Pacificplate along a subduction zone running 130km off the Pacific coast of northern Japan,the shock leapt from the first segment to a second and on to a third, extending the fault zonesome 400km and increasing its intensity more than 30-fold. With all the action taking placeonly 24km down, the seabed was thrust violently upwards, triggering huge waves.
有时,似乎沿这种特别的逆向断层的断裂会越过沿着缝隙的裂口及其他分界处,同该断层的其他部分连起来并且把断裂处拉长,甚至会出现危险。地质学中使用的传统的断层分割模型并不能解释这种现象。然而在灾难发生的这个周五,当北美板块沿日本北部的太平洋海岸旁边长130千米的俯冲带滑过太平洋板块后,冲击从第一个分割跳到第二个、随后又跳到第三个,断层地带被拉长到400千米,地震强度增加了30多倍。所有这一切活动都发生在据海平面仅34千米以下的地方,所以海床剧烈地向上猛推,引起惊涛骇浪。
Could such a chain of seismic events happen elsewhere in Japan? Many in Tokyo fear thatearthquakes may be creeping closer. The Japanese media have drawn attention to a quake ofmagnitude 6.6 on the far side of the country, between Nagano and Niigata prefectures, and toa quake of magnitude 6.1 in Shizuoka prefecture, both within days of the main quake. Butthese fairly common events occurred on entirely different tectonic plates. It is hard to imaginehow faults on one continental plate might communicate with those on another that ishundreds of kilometres away.
这种连锁地震可能发生在日本其他地方吗?很多在东京的人害怕地震也许离他们越来越近。日本媒体关注了一起发生在该国偏远地带、在长野和与新泻之间的6.6级地震,以及一起发生在静冈县的6.1级地震,这两次地震都发生在大地震后不久。然而这些相当平常的事件却是在完全不同的板块构造上发生的。很难想象一块大陆板块上的断层是如何同远在数千千米远的另一块断层发生相互作用的。
No doubt Tokyo will be sideswiped one day. The most likely spawning ground for thatearthquake will be 100km or more to the south-west, where the Philippine plate dives underthe Eurasian plate, creating a continuous sequence of shudders. This could feasibly cause amegaquake of the kind the north-east has just suffered. But the evidence remains largelyagainst it.
毫无疑问终有一天东京会受到擦边撞击。最有可能发生这一地震的地带也许是西南部100千米或更远的地区,那时菲律宾板块冲到欧亚板块下面,引发持续不断的摇晃。这极有可能引发像此次日本东北地区遭受的大地震。但是这一说法仍无无证据支持。
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