GWD24-第四篇新增五題

[freshmanduke]

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 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 common shallow events, in which the focus lay just under the epicenter, and deep events, with a 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.
1. The passage is primarily concerned with
(A) demonstrating why the methods of early seismologists were flawed
(B) arguing that deep events are poorly understood and deserve further study
(C) defending a revolutionary theory about the causes of earthquakes and methods of predicting them
(D) discussing evidence for the existence of deep events and the conditions that allow them to occur
(E) comparing the effects of shallow events with those of deep events
2. The author uses the comparisons to porcelain and putty (lines 2 and 8) in order to
(A) explain why the Earth’s mantle is under great pressure
(B) distinguish the earthquake’s epicenter from its focus
(C) demonstrate the conditions under which a Wadati-Benioff zone forms
(D) explain why S waves are slower than P waves
(E) illustrate why the crust will fracture but the mantle will not
3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.
4. The method used by Wadati to determine the depths of earthquakes is most like which of the following?
(A) Determining the depth of a well by dropping stones into the well and timing how long they take to reach the bottom
(B) Determining the height of a mountain by measuring the shadow it casts at different times of the day
(C) Determining the distance from a thunderstorm by timing the interval between the flash of a lightning bolt and the thunder it produces
(D) Determining the distance between two points by counting the number of paces it takes to cover the distance and measuring a single pace
(E) Determining the speed at which a car is traveling by timing how long it takes to travel a known distance
5. The passage supports which of the following statements about the relationship between the epicenter and the focus of an earthquake?
(A) P waves originate at the focus and S waves originate at the epicenter.
(B) In deep events the epicenter and the focus are reversed.
(C) In shallow events the epicenter and the focus coincide.
(D) In both deep and shallow events the focus lies beneath the epicenter.
(E) The epicenter is in the crust, whereas the focus is in the mantle.
answer: CEACD
想請問一下第三題 我是選C
第二段最後一句
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 rupture point.
根據句意 不就是C嗎?
想請教大家的意見
謝謝

[micht]

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. [highlight=yellow]Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves[/highlight]. Because P and S waves travel at different [highlight=pink]but fairly constant speeds[/highlight], the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.

3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?

前人不認為deep events存在 一直到Kiyoo adati採用a time difference between the arrival of primary (P) waves and the slower secondary (S) waves正命deep events存在 而此研究證明了deep events do occur.


題目要選下列哪一項MUST be true
因為文中有提到"fairly constant speed"因此不是絕對能夠用wave來判斷距離
也是有error的時候 因此如果要選哪一個絕對正確 則A比較好些

(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.

很久沒做題目
腦筋有點秀逗 有問題請大家多指教

[freshmanduke]

因為文中有提到"fairly constant speed"因此不是絕對能夠用wave來判斷距離 也是有error的時候 因此如果要選哪一個絕對正確 則A比較好些

這裡有點不懂 可否解釋一下
謝謝

[micht]

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 rupture point.

用wave來判斷距離....但作者說 P and S waves 兩個travel速度不同
但是fiarly constant 也就是說 P and S waves 的speed還算一致沒有太大的變化

還是有例外..

因為題目問must

所以答案不能做出一定絕對的距離判斷..我想

[freshmanduke]

原來如此
I see.
Thanks for your help!

[amyh]

請問這是出現在GWD-4嘛?
我找不到耶...

[freshmanduke]

GWD第24回 第四篇

[Winni]

給大家補充一下 文章內的focus(震源)跟epicenter(震央)的不同

震源（earthquake focus或hypocenter）:指地震發生的位置，即地震錯動的起始點
震央（epicenter): 指震源正上方的地表位置，即震源垂直投影至地表之位置

[stilalala]

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 rupture point.

用wave來判斷距離....但作者說 P and S waves 兩個travel速度不同
但是fiarly constant 也就是說 P and S waves 的speed還算一致沒有太大的變化

還是有例外..

因為題目問must

所以答案不能做出一定絕對的距離判斷..我想

還是不懂耶
我以為時間需要相對長
未必代表是深震

總覺得cor e來得合理些

可以在解釋一下嗎
腦筋轉不過來
謝謝

[uioxcv]

1. The passage is primarily concerned with
(A) demonstrating why the methods of early seismologists were flawed
(B) arguing that deep events are poorly understood and deserve further study
(C) defending a revolutionary theory about the causes of earthquakes and methods of predicting them
(D) discussing evidence for the existence of deep events and the conditions that allow them to occur
(E) comparing the effects of shallow events with those of deep events

為什麼這題要選c呢?defending a revolutionary theory ?感覺怪怪的~文中有提到嗎?
我是選 d耶~~文中主要在談的就是deep events 深層地震發生的原因不是嗎?

[小智]

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 rupture point.

用wave來判斷距離....但作者說 P and S waves 兩個travel速度不同
但是fiarly constant 也就是說 P and S waves 的speed還算一致沒有太大的變化
還是有例外..
因為題目問must
所以答案不能做出一定絕對的距離判斷..我想

我覺得應該是C 因為題目說P wave和S wave都是等速度 只是速度不同
不管fairly constant是不是有例外 基本上還是可以依據兩wave抵達的時間差推算出距離
(C) The earthquake focus was distant. 小弟認為"distant"這個字眼有兩種含意
一個是說震源(focus)在地表下很深 即深層地震
另一個則是遙遠的 (可以是深層或淺層地震)

而 (A) The earthquake was a deep event. 只解釋了一半
那很遠處發生的淺層地震同樣也會使量到的P wave和S wave間隔很久
又該如何解釋？ 還請各位指教

[auguding]

還是不太了解是A好還是C好
同意樓上的說法
the interval between their arrivals increases in proportion to the distance from the earthquake focus, or initial rupture point.

但 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.

啊不是說distant foucus代表deep event嗎?!

大家討論一下吧~~~

[dibert8]

3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(C) The earthquake focus was distant.

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 rupture point.
可以發現 (A) 是肯定的,但是 (C) 卻不一定.不管 focus (i.e. 地震發生點)發生點,只要是深層地震, S 波一定比 P 波晚到許久.重點在於 P 和 S 到達的時間差,和地震發生點發生點的絶對距離無關.

[auguding]

我有點不懂~
不是說FOCUS深究表示是DEEP EVENT嗎?
那麼 DISTANT FOCUS步就是說DEEP EVENT?
我好困惑~

[dibert8]

distant (遠): e.g. 震央在新疆下方 80 km, P (在新疆地面) / S (在新疆地下 80 km) 震波到達台北觀測站的時間差.
deep (深): e.g. 震央在台北下方 80 km, P (在台北地面) / S (在台北地下 80 km) 震波到達台北觀測站的時間差.
shallow event: e.g. 震央在台北下方 10 km
deep event: e.g. 震央在台北下方 80 km
focus: 震央
epicenter: 在震央正上方的地面