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The North American and Pacific plates meet in California at the San Andreas fault. The plates ____1____ past each other there at as much as an inch-and-a-half a year. Until the plates ____2____. Then ____3____ - an earthquake.
But on some active portions of the fault, the plates tend to just ____4____, without many violent jerks. All thanks, it turns out, to a little mineral lube, according to a study in the journal Geology.
Geologists got rock cores from two miles down, at the active fault zone. They looked at those fault rocks with an electron microscope. And they found an incredibly thin coating of clay polish on the rocks.
They say that clay layer apparently lubricates the plates - like greasing ball bearings - and that it's deposited there by mineral-rich water, sucked into the fault's ____5____. As the fault moves, it opens new cracks for the fluid to get into, which means more lube, and more smooth creeping. A process that's been going on for millions of years. So given enough time, parts of the fault seem to develop their own earthquake prevention mechanism. But for other sections, the clock's still ticking.
grind jam energy builds up, and eventually they lurch creep along nooks and crannies
太平洋板塊和北美板塊在加州圣安地列斯斷層交匯相接。這兩個(gè)板塊以每年一英寸半的速度摩擦、碰撞、相向運(yùn)動(dòng)。直至兩個(gè)板塊間緊緊擠壓，使能量逐漸聚集，最終使兩個(gè)板塊急傾、錯(cuò)裂，釀成地震。 不過在斷層的活躍部分，兩個(gè)板塊似乎僅僅是在緩慢滑動(dòng)，還沒有發(fā)生強(qiáng)烈的錯(cuò)動(dòng)。根據(jù)《地質(zhì)學(xué)》雜志上刊登的研究，這都要感謝礦物潤滑油——正是這小小的礦物潤滑油促成了這一現(xiàn)象。 地質(zhì)學(xué)家們在斷層帶活躍區(qū)域的兩英里深處采集了巖心樣本，他們利用電子顯微鏡研究那些斷層巖，發(fā)現(xiàn)這些巖石上覆蓋著極薄的一層粘土“拋光蠟”。 地質(zhì)學(xué)家們表示，顯然，粘土層在兩個(gè)板塊之間起著潤滑作用——就像潤滑滾珠軸承那樣，而且，粘土層能存積在兩板塊間是因?yàn)閿鄬拥慕锹渑c縫隙吸入了富含礦物質(zhì)的水分。當(dāng)斷層運(yùn)動(dòng)時(shí)，會(huì)形成新的裂縫，而液體會(huì)流入其中，這就意味著縫隙間有著更多的潤滑油，相互的摩擦、移動(dòng)也更平滑。這一過程持續(xù)了數(shù)百萬年。因此，這樣長此以往，一部分?jǐn)鄬铀坪跣纬闪俗约旱牡卣痤A(yù)防機(jī)制。不過，對(duì)于其他部分，地震危機(jī)依然迫在眉睫。