請將下面這段話翻譯成英文：
東漢時期，地震頻繁發(fā)生。通過對地震的一系列仔細觀測，張衡于公元132年發(fā)明了地動儀(seismograph)，它是世界上第一個用來識別和確定地震方向的儀器。 地動儀表面上鑄(cast)有八條龍，每一條龍的嘴里都有一個銅球。八條龍身下的地面上有八只仰著頭的銅蟾蜍（toad)，銅蟾蜍張著的嘴恰與龍口相對。當?shù)卣鸢l(fā)生時，面朝地震方向的龍口會張開，口中的球?qū)⒙淙塍蛤艿淖炖铮詣又该鞯卣鸬姆较颉?/p>
參考答案:
During the Eastern Han period，earthquakes occurred frequently. Through a series of careful observations of earthquakes，Zhang Heng invented the seismograph ,in 132 AD, which was the world's first instrument to identify and ascertain the direction of earthquakes. The seismograph is cast with eight dragons on the surface,and each dragon has a copper ball in the mouth. On the ground below the dragons there are eight copper toads raising their heads and opening their mouths opposite to the dragons'mouths. When an earthquake occurred, the dragon facing the direction of the earthquake would open its mouth，and the ball in its mouth would fall into the toad's mouth, automatically indicating the direction of the earthquake.
1.東漢時期，地震頻繁發(fā)生:“發(fā)生”可用occur表達；“頻繁”可翻譯為frequently。
2.通過對地震的一系列仔細觀測:文中翻譯為through a series of careful observations of earthquakes。
3.用來識別和確定地震方向:“識別”可用identify表達；“確定”可翻譯為 ascertain。
4.面朝地震方向的龍口會張開:“面朝”可用face表達。
5.指明:文中翻譯為indicate。
