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USGS(美国地质勘探局)没有预报过天水、西安等地有可能发生7级以上强震的预报
(博讯北京时间2008年5月23日 转载)
(博讯编者按:在此文之前,博讯已经对原报道加了按语,应该属于供稿的朋友误读了美国地震局的图表。关于地震有无办法预测问题,近期中国官方发出预报有强余震,说明一定程度上可以预报。就像天气预报一样,地震预报只是时间和精度问题,不是不可以预测的事情。美国不是也有共识,加州30年内99%会发生强震?)

来源:参与 作者:沧海
    
    
USGS(美国地质勘探局)没有预报过天水、西安等地有可能发生7级以上强震的预报

 来源:参与 作者:沧海

《参与》记者近日就一则流传甚广的地震预报(博讯相关报道链接 http://news.boxun.com/news/gb/intl/2008/05/200805211229.shtml)采访了USGS(美国地质勘探局)的有关专家,得到了可靠回复,USGS(美国地质勘探局)没有预报过天水、西安等地可能发生7级以上强震的预报,并且该预报对USGS官方网站上发布的图表存在严重误读。

问题一: 最近有一则据说是USGS(美国地质勘探局)预报的消息在中国民众间 流传甚广。全文如下:“四川汶川地震震源向东北方向移动,地壳已经出现大范围持续破裂,震源现在奔着西安方向延伸,目前延伸大致方向是天水和西安中间。未来2星期内:天水、西安、甘肃等地有可能将连续发生7级以上的强震,请当地居民提前防犯。”(并附了链接http://earthquake.usgs.gov/eqcenter/recenteqsww/Maps/10/105_30.php was attached to the news)

请问USGS预报过这样的消息么?USGS对于四川汶川大地震的余震做怎样的预测?

Q1:A news was spreaded popularly in Chinese public and was said to be a USGS forecast. The whole content is: The epicentre of Sichuan Wenchuan Earthquake is transfering to northeast direction, the earth's crust has appeared large-scale and continuous cracking, the epicentre is extending to Xi'an, and the rough extending direction is between Tianshui and Xi'an. In the future two weeks, strong shocks up to magnitude-7 may continuously happen in Tianshui, Xi'an and some area of Gansu Province. Local citizens should keep alert of that in advance. (this link http://earthquake.usgs.gov/eqcenter/recenteqsww/Maps/10/105_30.php was attached to the news)

Did USGS ever forecasted above news? What did USGS forecast on the aftershocks of Sichuan Wenchuan earthquake in fact?

问题二:一些中国专家告诉民众地震不可预测。他们的理由如下:地震过程的复杂性;地壳深部的不可入性;地震事件的小概率性。

您怎么看以上这个观点?您认为地震是否可以预测?

Q2: Some Chinese professionals said to the public that earthquake can not be forecasted. Their reasons are: the course of earthquake is very complicated; the deep part of earth crust can not be entered into; little probability of earthquake occurrence.

What's your opinion on above views? Do you think earthquake can be forecasted or not?

USGS(美国地质勘探局)专家Paul Spudich博士的回复如下:

谢谢你提出的问题,你的问题附在后面。你可以把我的回答转发给任何人,包括转发给发布那则新闻的机构。

USGS(美国地质勘探局)不做地震预报。关于USGS所做预报的报道完全是虚假的。

请看这个链接:http://earthquake.usgs.gov/eqcenter/eqinthenews/2008/us2008ryan/finite_fault.php



Figure 4. Surface projection of the slip distribution superimposed on ETOPO2. The black line indicates the major plate boundary [Bird, 2003].

当5月12日的主震发生时,一个300公里长的断裂带(大概是龙门山断裂带)滑动,整个断裂带的滑动持续了约2分钟。图4为断裂滑脱区的示意图(颜色代表滑动的数量)。可以看得出来,滑脱区从震中(滑动开始的地方)向东北方向延伸了约250公里。

余震通常发生在主震的断震带或其附近。在那则新闻中出现的链接:http://earthquake.usgs.gov/eqcenter/recenteqsww/Maps/10/105_30.php,显示了5月12日主震之后的余震分布。



对比图4和这张余震分布图,可以发现5月12日地震后的余震位于非常接近主震断裂带的地方。这也是大部分地震余震通常呈现出的现象。

那则新闻称,“四川汶川地震震源向东北方向移动,地壳已经出现大范围持续破裂,震源现在奔着西安方向延伸,目前延伸大致方向是天水和西安中间。”这是对于余震分布错误的解释(如果“转移”和“延伸”意味着一天一个变化)。它将余震的东北向曲解为余震向西安方向运动。余震不会向任何地方移动。余震只会停留在主震断裂区域的附近。余震的东北向是相对于主震断裂区域的方向而言。

“未来2星期内:天水、西安、甘肃等地有可能将连续发生7级以上的强震”。这一说法没有任何科学依据。西安和天水离余震区很远,因此5月12日的主震不可能在西安和天水附近导致强震。USGS没有预报过这样的地震。

在四川地震后已经发生过多次余震,在未来几个月中余震还会继续。余震的震中可能保持在主震断裂带附近。迄今为止,最大的余震达到了6级,而且这样大的主震的余震可能会达到7级以上,但是我们不能预测出未来余震发生的时间和地点。

那则新闻称,“地壳已经出现大范围持续破裂”。这可能是指主震导致的地面破裂,这在强震后是很常见的,但我本人不知道有什么破裂。当断裂层滑动,就会使地面破裂。在2001年11月发生的地震中,地面破裂沿中国青海境内的昆仑山地震断裂层长达350公里。

USGS和其他科学家正在观测7.9级的地震是否会将压力转移到该区域其它主要的活性断层,这些问题是否会导致附近区域产生问题,但这项研究是非常不确定的,并且这项研究不会对地震发生的时间做出任何预测。

中国国家地震局就反驳地震预测的谣言发表了郑重声明。该声明为伦敦时报在线文章所引用:
http://www.timesonline.co.uk/tol/news/world/asia/article3968327.ece

被引用的声明称:“任何关于地震在确切的时间和地点发生的预测必定是谣言。因为当前世界的地震预测水平不可能达到如此精确的程度。”

USGS同意这一声明。

向中国的死难人民表示哀悼。

地球物理学者 Paul Spudich博士

Thank you for your question, which is appended below. You may forward my response to anyone, and you may forward my response to the news agency that wrote the report which you sent to me.

The USGS does not make earthquake predictions. The reports of USGS predictions are completely false.

Please look at:

http://earthquake.usgs.gov/eqcenter/eqinthenews/2008/us2008ryan/finite_fault.php

When the May 12 main shock occurred, a 300-km-long section of the fault (probably the Longmenshan fault) slipped, taking about 2 minutes for the entire fault to slip. Figure 4 shows a map of the slipped region of the fault (the colors show the amount of slip). As you can see, the slipped area extended about 250 km NE from the epicenter (the place where the slipping started).

Aftershocks usually occur on or near the part of the fault that slipped in the main shock. The link that appeared with the news report:

http://earthquake.usgs.gov/eqcenter/recenteqsww/Maps/10/105_30.php

shows a map of the aftershocks of the May 12 main shock. If you compare Figure 4 and the aftershock map, you can see that the aftershocks of the May 12 earthquake are located very close to the part of the fault that slipped in the main shock. This is the usual behavior of most earthquakes’ aftershocks.

The news statement, “The epicentre of Sichuan Wenchuan Earthquake is transfering to northeast direction, ... the epicentre is extending to Xi'an, and the rough extending direction is between Tianshui and Xi'an.“

is an incorrect interpretation of the aftershock distribution (if ‘transferring’ and ‘extending’ imply a change from day to day.) It misinterprets the northeast orientation of the aftershock zone to imply motion of the aftershocks toward Xian. The aftershocks are not moving anywhere. They are staying close to the slipped area of the main shock. The northeast orientation of the aftershock zone is caused by the northeast orientation of the slipped zone in the main shock.

There is no scientific basis for the news statement, “In the future two weeks, strong shocks above 7 level may continuously happen in Tianshui, Xi'an and some area of Gansu Province.“ Xian and Tianshui are far from the aftershock zone, and it is very unlikely that the May 12 main shock will cause big earthquakes near Xian or Tianshui. The USGS did not predict any such earthquakes.

There have been many aftershocks following the Sichuan earthquake and these will surely continue in the coming months. Their epicenters will probably remain close to the slipped part of the main shock fault. The largest aftershocks until now have been in the magnitude-6 range, and aftershocks for such a large main shock can possibly range up to magnitude-7, but we cannot predict the time and location of future aftershocks.

The news statement, “the earth's crust has appeared large-scale and continuous cracking“ might refer to the appearance of ground cracking caused by the main shock, which is common after large earthquakes, but I do not personally know of any cracking. When faults slip, they crack the ground. Ground cracks extended about 350km along the Kunlunshan, Qinghai, China earthquake fault during the November 2001 earthquake.

USGS and other scientists are examining whether the magnitude-7.9 earthquake transferred stress onto other major active faults in the region, and whether those other faults may have been brought closer to failure, but that research is very uncertain and that research does not make any prediction of earthquake occurrence times.

The Chinese State Seismological Bureau has broadcast a strongly worded statement refuting rumored earthquake predictions. The statement quoted in this London Times Online article:

http://www.timesonline.co.uk/tol/news/world/asia/article3968327.ece

The quoted excerpt is: "Any 'prediction' of an earthquake at a certain time and in a certain place is certainly a rumour. Because currently in the world the level of earthquake prediction is impossible to achieve this kind of accuracy."

The USGS agrees with this statement.

Regards, and condolences for your great nation’s great loss,

Paul Spudich, Ph. D.

Geophysicist

此外,据USGS的另一位专家Lisa Wald介绍,USGS的研究重点是地震位置的长期预测(地震的灾害评估),建立相应的数据库和快速的地震后信息,以在强震区采取紧急反应。

“Our focus is on long-term forecasts of earthquake location (seismic hazard assessment), which enables building codes that are adequate to the task, and rapid post-earthquake information so that emergency response can be focused in zones of highest shaking.”Said by Lisa Wald, Geophysicist, Web Team Leader, USGS Earthquake Hazards Program.


_(博讯记者:杨逸) (Modified on 2008/5/24) (博讯 boxun.com)

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