The scientists who study the seismic waves（地震波） released from the focus of an earthquake are called seismologists （地震學家）. Special measuring instru- ments， called seismographs（地震儀）， record the pattern of the seismic waves. Seismologists use these patterns to deter- mine the strength and duration（持續(xù)時間） of an earthquake， as well as the amount of movement along a fault¹ line. Taking readings at several different points on the earth's surface also helps them to pinpoint² the exact location of the earth- quake' s focus（震源）.

Two different scales （等級） are used to measure the strength of an earthquake. The most common one is the Richter scale， devised by American seismologist， Charles Richter， in 1935. It calculates the magnitude （震級） of an earthquake from seismograph recordings that measure the amount of energy released. An increase of 1 point on the Richter scale means that an earthquake is 10 times stronger than one with the next value （數值） below. An earthquake measuring less than 5 on the Richter scale causes minimal³ damage， while a major earthquake measures 7 or more. The second scale is the Mercalli scale， which calculates the intensity（烈度） of an earthquake by assessing（對……估價） the damage it causes.

One type of seismograph records the horizontal （水平的） movements of the earth， and the other type vertical（垂直的） movements. For the horizontal seismograph， a weight is attached to a frame (支架) by a sensitive spring (彈簧). As the ground trembles(抖動)， the weight remains stationary(穩(wěn)定的) but the frame moves and a pen records the movement on paper wrapped⁴ around a rotating (旋轉的) drum. This recording is called a seismogram(震波圖).

注釋：

1．fault n．[地]斷層

2．pinpoint vt．精確地確定…的位置

3. minimal adj.最小的，最低限度的

4．wrap vi. 纏繞，盤繞

5．crack vi. 裂開，破裂

6. surface waves面波，它是一種在地表傳播的地震波，能量很大。

研究地震源向外釋放的地震波的科學家稱為地震學家。地震儀是專門測量記錄地震波圖形的儀器。地震學家利用這些圖形判斷地震強度和持續(xù)時間以及沿地震帶斷層的移動幅度。從地球表面不同地點采集的數據也能幫助他們確定震中的精確位置。

地震強度可用兩種不同的震級測量。最常用的是由美國地震學家查爾斯·里克特于1935年設計的里氏震級。它根據地震儀所記錄的地震釋放出的能量計算震級。里氏震級每上升1級，震強增加10倍。震級為5級以下的地震造成輕微損壞，7級或7級以上為大地震。另一種是麥加利震級，它根據估測地震所造成的破壞程度計算地震強度。

有一種地震儀記錄地球的橫向活動，另一種記錄縱向活動。水平地震儀是用靈敏彈簧把一重物掛在支架上。地面顫動時，重物保持不動，而支架移動。有一支筆將移動信息記錄在纏裹于轉鼓上的紙上。所記錄的信息稱做震波圖。

記錄地面縱向運動的垂直地震儀示意圖

1: Felt by only a very few people.

2: Felt by a few， on upper floors.

3: Similar to a passing vehicle.

4: Felt by many people indoors.

5:Buildings tremble and trees shake.

6: Felt by all. Plaster(灰泥) cracks5.

7: Bricks loosen. Difficult to stand.

8: Damage to weak structures.

9: Pipes crack. Buildings collapse.

10: Huge ground cracks. Landslides(滑坡).

11 :Most buildings destroyed. Tsunamis (海嘯).

12: Total destruction. Surface waves6 seen.

記錄地面橫向運動的水平地震儀示意圖

1級：只有極少數人感覺到。

2級：在樓上的少數人感覺到。

3級：如同車輛駛過般的震動。

4級：室內許多人能感覺到。

5級：建筑物顫動，樹木搖晃。

6級：人人感覺到。墻泥裂縫。

7級：磚頭松動。站立困難。

8級：不堅固建筑物受到損壞。

9級：管道破裂。建筑物倒塌。

10級：大片地面斷裂。出現滑坡。

11級：大部分建筑物毀壞。發(fā)生海嘯。

12級：徹底破壞。出現面波。