广州11月3日一战750，一点狗狗

吉木乃

不知道LZ说的那片地震阅读是不是【GWD-24-Q30 ~ 37 GWD24-passage four深层地震的成因探析】？求确认。
In most earthquakes the Earth’s crust cracks like porcelain. Stress builds up until a fracture forms at a depth of a few kilometers and the crust slips to relieve the stress. Some earthquakes, however, take place hundreds of kilometers down in the Earth’s mantle, where high pressure makes rock so ductile that it flows instead of cracking, even under stress severe enough to deform it like putty. How can there be earthquakes at such depths?
That such deep events do occur has been accepted only since 1927, when the seismologist Kiyoo Wadati convincingly demonstrated their existence. Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done, Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or initial rupture point. For most earthquakes, Wadati discovered, the interval was quite short near the epicenter; the point on the surface where shaking is strongest. For a few events, however, the delay was long even at the epicenter. Wadati saw a similar pattern when he analyzed data on the intensity of shaking. Most earthquakes had a small area of intense shaking, which weakened rapidly with increasing distance from the epicenter, but others were characterized by a lower peak intensity, felt over a broader area. Both the P-S intervals and the intensity patterns suggested two kinds of earthquakes: the more (45) common shallow events, in which the focus lay just under the epicenter, and deep events, with focus several hundred kilometers down.
The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones), where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
本文体会通篇的对比。
在大多数地震里，地壳瓷般碎裂。压力聚集，直到破裂在数公里深处形成，地壳滑动以释放压力。但是有些地震在数百公里深的地幔发生，虽然在那里压力巨大，岩石变得柔软，浮动而不破裂。这种地震如何发生？<, BR>深层地震到了1927年才被接受为事实。前人通常比较不同地点震波的到达时间，而KW则比较P波和S波到达时间的差别。因为P波和S波以不同的连续速度行进，它们到达的间隔随震源距离成比例增长。KW发现，在震中（地表摇得最厉害的地方）附近的间隔较短，但是某些情况下，即使在震中附近间隔也很长。振动密度数据也呈类似结果。大多数地震有一个密集振动的范围，振动随震中距离加大而迅速减少，但是另外一种地震的特点是更广范围更低峰值的强度。P-S间隔和强度类型都暗示了两种地震：更常见的浅层地震，震源在震中下面；还有深层地震，震源在数百公里深处。
问题持续：什么导致了深层地震，既然地幔软得不足以存储压力？KW的实验显示，深层地震出现在一块地壳板块被另一块挤向下方地幔之处。下降的岩石比周围地幔冷一些，所以不那么软，更容易碎裂。

ttss

怎么没瞬间拿出手机拍下。。。。唉。。
黑衣MM来个小马甲吧～

leeyuan1

牛！祝申请顺利

amumu

MM快出现吧~直接签了F2就走啦~

-- by 会员 babee2queen (2009/11/3 21:49:36)

发展的真快啊，哈哈

vickyye

我也感觉LZ说的就是GWD的题.....

vickyye

MM只有考完了才会有心情搭理GG呀..不然GG考那么好..MM自己没考好..那多郁闷..

amumu

明天就考了，看了你的帖子，真是鼓舞啊，哈哈

XYXB

大牛，黑衣高挑PLMM你就先别想了，先帮我确认考古吧，既然不是GWD的那篇，我找了半天只找到一个版本：

V1

考了地震那一题，但确定不是GWD上那篇，但背景内容相近。

第一段：讲一个Long-established theory，而且大多数地震都是在高温高压下facture断裂，而且在地表less than 40 miles的地方发生。

第二段：讲有个学者发现有些地震发生得离地表很深，有两个理由解释这个，一个是phase什么，是个术语不认识但不影响解题，这个东东发生得很慢所以用来解释地震不合适，另一个什么，又是一个术语，跟前一个只有前面一个字不同，恰好解释了深层地震。

题目1问第一段讲大多数地震的情况暗示了什么，我选大部分地震都是符合传统那个理论的题目2 问第二段两个术语代表的过程有什么不同和相同点，选项中都有两方面，问哪个符合原文。

hispeed

是的是的，就是这篇
在这里也要感谢XYXB和各位整理寂静的G友，帮大忙了

lzj1209

专业围观~~呵呵~~