
In a South African gold mine 12,000 feet (3,700 meters) underground, USGS geologist Malcolm Johnston, at right, and University of Oklahoma graduate student Vincent Heesakkers prepare to install instruments that will help them understand the physics of an earthquake. A fault-a crack in the Earth's crust-runs through the mine. By monitoring the fault, the scientists hope to learn how strain builds up along faults as the crust shifts and deforms over time, and how they ultimately give way in earthquakes. A fault is essential for creating any deposit of gold, as mineral-rich fluids pumping through the fissure for eons gradually concentrate the ore there. "If you want to find gold," says Johnston, "go look for a fault-an old one."
在南非一处地底下3700公尺深的金矿内,美国地质调查所的地质学家麦克兰·强斯敦(右)与俄克拉荷马大学研究生文森·海萨柯尔斯准备安装仪器,好帮助他们了解地震物理学;这座矿坑里有一个断层(地壳的破裂)穿过。藉由监测这个断层,科学家们希望了解在地壳移动及随着时间变形时,张力是如何沿着断层增加、最后又是怎样转化为地震。断层是黄金矿床形成的要素,而富含矿物的流质由岩石上的裂缝泊泊冒出,经年累月,最后集结成了矿物。强斯敦说:“要是想找黄金,就到断层去,而且要找老的矿坑。”(摄影:彼得·艾席克) |